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The gut microbiota is the hottest of hot research fields today. The microbes that inhabit our intestine are more than passive freeloaders living off the food we eat. With a thriving mix of beneficial bacteria, our gut microbiome can keep us healthy.
Immunity, mental health, diabetes and even body weight make up the fascinating areas covered in the ever-growing research field of the gut microbiota. That last point about body weight is the one getting a lot of attention from obesity researchers. New evidence finds that gut bacteria can alter the way we store fat, balance levels of glucose in the blood, and even how we respond to hormones that make us feel hungry or full.
The gut microbiota and microbiome explained
The gut microbiota is a complex system made up of our resident bacteria, viruses and other microbes that have colonised the gastrointestinal tract. You may sometimes hear the term gut microbiome used. All the genes inside the microbial cells are what create the microbiome. The two terms microbiota and microbiome are often used to mean the same thing.
The microbiota creates its own mini ecosystem in the same way that plants, animals and insects live together in their own delicate ecosystem in a rainforest. We have a skin microbiota, mouth microbiota and in females, a vaginal microbiota. Then there is the one that receives the most attention: the gut microbiota. The entire microbiota in our gastrointestinal tract weighs between 0.5 to 2 kilograms.
One-third of our gut microbiota is common to most people, while two-thirds are specific to each one of us. This makes our gut microbiome as unique as our fingerprints.
The gut microbiome is not a static thing. It changes throughout life after first colonising the gut shortly after birth and continuing to gather new members from the environment throughout life. Variation is highest during childhood, and it gradually decreases with age. Illness, antibiotic use, fever, stress, injury and dietary changes all affect the blend of microbes that make up the microbiome.
Gut bacteria and weight
The spotlight on what influences our weight usually focuses on a poor diet, sedentary lifestyle and the genetic cards dealt to you at birth. But as evidence continues to snowball, should we also be looking further inside us at our gut microbes?
An early clue that gut microbes might play a role in obesity came from studies comparing intestinal bacteria in obese and lean twins. Lean twins have a more varied ecosystem of gut microbes compared to an obese twin sibling.
The twin studies make fascinating observations, but don’t prove that it is the gut bacteria that are the cause of the weight difference. The twin studies illustrate how complex a condition obesity is. Genetics and early life colonisation by bacteria only explain part of it. Diet can affect the mix of gut bacteria, with a highly processed diet low in food variety and fibre translating into less diversity of gut microbes.
From the human twin studies, the next move was to manipulate the gut bacteria of mice to see if body weight changes would follow. Identical mice inoculated with microbes from human obese and thin twins served as the model. Mice inoculated with bacteria from an obese human twin gained more weight and had a less diverse community of microbes compared to mice inoculated with bacteria from the thin twin.
So how could microbes affect our weight? One plausible mechanism is by altering our appetite. A French research team found that microbes make hormones involved in appetite regulation 20 minutes after being given nutrients. Giving these appetite hormones to mice saw them eat less food. It is no coincidence that the 20-minute mark after a meal is around the time it takes for a person to feel full. Eating slowly makes for sage advice so that gut microbes can ramp up production of appetite hormones, meaning you’ll stop eating earlier.
The research field is moving rapidly with clinical trials now up and running to ‘transplant’ freeze-dried bacteria from the faeces of lean and healthy donors into volunteers as a weight loss treatment. It’s probably not the most pleasant treatment that you can imagine, but there’s strong evidence that faeces are good for the microbiome environment inside our guts.
How what we eat affects our bacteria
You are what you eat, and so are the bacteria that live in your gut. The different strains of bacteria change depending on the types of food eaten. We have some way to go to know what the ‘perfect’ diet may be for gut health, but it will likely be very individual.
The dietary pattern linked most to an adverse change in bacterial species is the highly refined typical Western diet high in sugar and low in fibre. The good news is that a shift to a healthier diet can change the bacteria mix in a few days.
The key theme of healthy long-lived communities around the world is a diet high in plant-based foods. Across the spectrum, the Mediterranean diet gets top marks as a healthy balanced diet. It is distinguished by a beneficial fatty acid profile that is rich in both monounsaturated and polyunsaturated fatty acids, high levels of polyphenols and other antioxidants, high amounts of fibre, and lots of plant-based foods.
The Mediterranean dietary pattern is one that stands out for the variety of foods eaten and ticks most of the boxes for a microbe-friendly diet. Legumes, fruits, wholegrains, olive oil, yoghurt, dairy, nuts, seeds, vegetables and fish are a feast for your gut microbes.
Weight rebound is a far too common result of most weight loss attempts. For some, the weight comes back on with interest. Gut microbes could be playing a part here too.
Using a yo-yo dieting model in lab mice, Israeli scientists found that yo-yo dieting mice had less diversity in their gut microbes compared to mice eating normally. They also regained weight rapidly. The changes to the gut microbiome brought about by obesity stayed put for far longer than the time spent dieting. This could explain why it is so hard to lose weight when you try your next diet – your gut microbes are still reeling from the effects of the last diet
So take a guess what happened when normal-weight mice received microbes from yo-yo dieting mice? Yes, they gained weight. These inoculated mice also digested fibre less efficiently. Fewer beneficial by-products were made from a class of plant chemicals called polyphenols. Polyphenols can act as a prebiotic, increasing the number of healthy bacteria in the gut. Fruits, vegetables, dark chocolate and tea are good sources of polyphenols and make great food for our gut microbiome.
What does all this research for me?
Laboratory studies in mice are all well-and-good to explore a theory, but what does it mean for us? Can a change in diet change the population of our gut microbes? And will that mean a change in weight?
A recent study involving African-Americans who swapped their meat-heavy, highly processed diet for a diet typical of African foods rich in beans and vegetables saw a positive change gut microbes within 2 weeks. And the reverse swap that saw rural Africans switch to a typical American diet gave them a microbe profile that was more in line with a higher risk of colon cancer.
Two weeks is a short time, but long enough to make changes to the microbe population that can alter our risk of disease. Will this guarantee weight loss? Not always, but the food swaps recommended are in line with guidelines already in place for better health and lowering chronic disease risk. Bringing in the angle of the gut microbiome gives these guidelines even more credence.
What about probiotics?
A less studied area is the potential effect of probiotics on body weight. Gut bacteria have been linked to how fat is stored, how glucose levels are regulated and even how hormones involved in making us feel hungry or full are regulated. The wrong mix of microbes could worsen problems for someone struggling to control how much food they eat.
So the big question is: can taking a probiotic supplement help with weight loss? And the answer appears to be ‘yes’; at least according to a systematic review and meta-analysis of clinical trials. Twenty-five randomised controlled trials involving close to 2,000 people informed the review. The trials were made up of a mixture of healthy adults, people with type 2 diabetes, people with high cholesterol or hypertension and people with non-alcoholic fatty liver disease. Most of the people were overweight or obese at the start of the studies.
All trials included both a group receiving either one or a combination of several probiotic supplements and another group receiving a placebo. The difference in weight loss between the two groups was in favour of the probiotic supplement with an additional 0.54 kg lost. This may not seem like a lot, but it represented additional weight lost compared to any other diet or physical changes the people were making.
Digging a bit deeper, it seemed that trials that used multiple strains of probiotics gave a greater weight loss benefit. And the longer the study ran for, the more likely that weight loss happened. Because so many different strains of probiotics were used it is not possible to narrow in on which protocol may work best for weight loss.
A probiotic supplement or food is not some magical panacea for obesity. But the findings from this latest review give some validity to the theory that our gut microbes have some sway in controlling what we eat and how we regulate our weight. There are too many over-hyped ineffective weight-loss supplements that fill shelves, but at least for probiotics the case for their use has some validity.
Top foods to improve your gut health
Look after your gut microbes and they will look after you. And to do that, you want to feed them the right food. Gut microbes ferment prebiotic foods which can then stimulate the growth of beneficial bacteria. Here are my top tips to keep your gut microbes well fed and thriving.
Eat as many different plant-based wholefoods as possible. Some top prebiotic foods to include are:
Barley and oats
Foods high in resistant starch such as legumes, green bananas and cooked and then cooled potatoes are a great fermentable fuel source for bacteria
Fermented probiotic foods like sauerkraut, kimchi, kefir and yoghurt are good sources of beneficial bacteria.
The gut microbiome into the future
Understanding the health implications of the gut microbiome is very much at an early stage. A fascinating peek into what could lie ahead is having dietary advice tailored to a person’s own unique microbiome signature.
Only two years ago, Israeli researchers attracted worldwide attention by successfully predicting a person’s blood glucose response to food by personalising their diet according to their gut microbiota profile as one of several factors.
The practical implication of gut microbiome research boils down to some simple basics: eat a variety of minimally processed plant-based foods high in fibre and move away from the ultra-processed foods that are over-represented in the Western diet. In the future, a personal consultation for diet advice for health, weight loss and disease risk could also involve a swab, petri dish and microbiologist.
Bowel cancer ranks as one of Australia’s most common cancers, especially for people aged over 50. This is one form of cancer where diet and lifestyle choices play a big part in changing a person’s risk of developing it. That makes it a good news story because lifestyle factors are changeable. Here I outline the key lifestyle habits to consider looking at.
Bowel cancer (also called colorectal or colon cancer) is the second biggest killer of Australians from cancer each year. Over 16,000 people are diagnosed with bowel cancer every year in Australia.
Bowel cancer can occur in any part of the colon or rectum, either growing from the inner lining of the bowel or from small growths on the bowel wall. Undetected, bowel cancer can spread into the wall of the bowel, the lymph nodes and then on to other organs.
Lifestyle factors account for half of all bowel cancer cases. Another quarter of cases are explained by genetics and family history. Not eating enough fibre, having too much red and processed meat, obesity (especially if the fat is around the abdomen), smoking, physical inactivity and alcohol are the key lifestyle factors with the most evidence for upping the risk of colorectal cancer.
So it is timely that only this month, the World Cancer Research Fund put out a major update into the lifestyle factors linked to bowel cancer.
Bowel cancer and lifestyle: the WCRF update
The World Cancer Research Fund is the world’s leading authority on the link between diet, weight, physical activity and cancer. When they put out reports, you can count on the information being backed by the world’s leading cancer scientists and a wealth of research.
Way back in 2007, the WCRF made some clear recommendations into lifestyle factors that influence bowel cancer risk. But research is never static, and recommendations are continually updated as new information becomes available. That is why the WCRF publishes updates as part of their Continuous Update Project. Among experts worldwide, the updates are a trusted, authoritative scientific resource, which underpins current guidelines and policy for cancer prevention
So here we have hot off the press the latest update: a new report on colorectal cancer. For the report, the global scientific research on diet, nutrition, physical activity and colorectal cancer was collected and analysed by a research team at Imperial College London, and then assessed by an independent panel of leading international scientists.
At 111 pages in length, the report is a lot to digest. But fear not that you need to wade through it all. The WCRF has produced an awesome infographic giving you the summary which sits below. After looking over the infographic, I will go into a bit more depth into five of the key factors.
If you want more information on the other factors linked to bowel cancer, then the full report has you sorted. And for a bonus, near the end of this article, I will look at the one factor that may have caught your attention on the infographic. And that is how your height can affect cancer risk. Don’t worry, there is nothing you can do about it, so focus instead on the other five areas!
There is a good reason why wholegrains feature in dietary guidelines around the world and it is not to annoy those who are a bit too ingrained (see what I did there?) to low-carb or Paleo diets. Just how good wholegrains are for us was unveiled in a recent major scientific review looking at diet and chronic disease.
Covering decades of research and hundreds of studies, the review found that plant foods, especially wholegrain foods, were linked to a lower risk of type 2 diabetes, overweight and obesity, cancer and cardiovascular disease.
So when the WCRF looked at foods that can decrease the risk of bowel cancer, wholegrains scored high marks. Wholegrains are a source of dietary fibre which on its own can help reduce bowel cancer risk. Fermentation of fibre in the colon results in the production of short-chain fatty acids that lower the pH of the colon. A lower pH slows down the proliferation of cancer cells and decreases the production of toxic by-products.
Wholegrains are rich in antioxidants, including trace minerals and phenolic compounds, which have been proposed to be important in cancer prevention. The fibre in wholegrains can also speed up the transit time of food through the gut, increase the bulk of stools and even help reduce the risk of insulin resistance.
2. More fibre for the win
Following on from the benefits of wholegrains, eating more fibre will help cut the risk of colorectal cancer. Which is another way of saying to eat more plant-based foods as that is the only place you’ll find fibre in your diet.
Fruits vegetables and beans are all great sources of fibre. And of course, wholegrain foods too, just in case you skipped reading the previous section.
3. Eat less red meat
People who eat a diet low in processed and red meat are less likely to develop bowel cancer. This link is nothing new and only in 2015, the International Agency for Research on Cancer (IARC) released a report investigating how likely red meat and processed meats are to cause cancer. The IARC concluded that processed meat and also likely red meat are linked to causing colorectal cancer.
Yet even the highest-level committee members of the IARC were not saying that if you eat a sausage you are a candidate for cancer. What they were warning about was that if processed meats were a daily feature of your diet, your risk of bowel cancer would go up.
So what is it about red and processed meats that can make them carcinogenic? The answer isn’t certain, but several plausible mechanisms have been proposed.
The first culprit is the haemoglobin pigment that gives red meat its colour. Haemoglobin breaks down to a family of chemicals called N-nitroso compounds in the gut. These compounds can damage the cells that line the bowel, causing them to divide and replicate more.
A second candidate could be the actual cooking process of red meat itself, especially grilling or barbequing. The combination of high temperatures and charring of meat produces chemicals on the surface of the meat that may increase the risk of colon cancer. One simple way to reduce the formation of these compounds is to marinate meat first. Think of it as a protective layer on the meat, but with the added bonus of extra taste.
Yet another theory is that the high iron content of meat could be the culprit. Iron is important for our health, but too much of it can place a higher oxidative stress (a process not unlike ‘rusting’) on the body, and damage cells lining the large bowel.
While a sausage sandwich every now and then isn’t going to do you much harm, if you are eating a lot of processed and red meat then it could be a good idea to try to cut down. The World Cancer Research Fund recommends eating no more than 500 grams of cooked red meat per week. And if you eat processed meat, really keep that to a minimum. Chicken and fish make excellent alternatives to red meat. Or you could even consider having more vegetarian meals in your diet. Time to get on the #MeatFreeMonday trend.
4. Get more active
Physical activity is recognised as a potent ‘cancer-preventing’ habit. Estimates link regular physical activity to a 20 to 40 percent lower risk of colon and post-menopausal breast cancer. There is also a potential benefit of exercise in lowering prostate cancer risk too.
Besides its cancer-prevention benefit, physical activity plays a large part in preventing heart disease and diabetes so the health benefits really add up.
In the WCRF report, the evidence was strong and consistent that high levels of recreational physical activity were protective against colon cancer. Physical activity helps reduce body fatness (which is linked to colon cancer risk) which leads to a reduction in insulin resistance and inflammation – both of which are part of colorectal cancer development.
The more active you are, the greater the benefits you can gain and it is never too late to start.
And as an aside, an evolving field of research is looking at how physical activity can help people already diagnosed with cancer. Several research studies are now linking regular physical activity after a cancer diagnosis with lower rates of cancer-related mortality, particularly from breast and colorectal cancer. These findings are important when you consider that thanks to earlier detection and improved treatments, more people than ever are surviving cancer.
5. Keep body weight in check
Keeping a healthy weight not only cuts your risk of bowel cancer, but could also reduce your risk of nine other types of cancer too. The evidence for bowel cancer and excess body weight in the WCRF report was consistent with a clear dose-response: meaning more weight equates to a higher cancer risk.
The link between excess weight and cancer could be from how our bodies can change hormone levels and produce chemical messengers, which in turn can increase cancer risk. High body fatness is associated with increased levels of insulin, which can promote cell growth and inhibit normal programmed cell death (called apoptosis).
Obesity is normally seen together with chronic low-level inflammation, which over time can cause DNA damage that leads to cancer. People who are overweight or obese are more likely to have conditions that are linked to or that cause chronic local inflammation.
Losing weight is easier said than done, and the WCRF don’t recommend any specific type of diet. Focus first on the wins you can achieve for the other lifestyle factors linked to cancer risk. Then consider a dietary change that connects with you – there is no one best way to lose weight.
Don’t be tall? WTF?
Here was a surprising one: being tall elevates the risk of colorectal cancer. Not much anyone can do about that one I’m afraid, but why is it so?
How tall a person grows is influenced partly by their genes and partly by the nutritional quality and quantity of their diet during the growing phases of their life. A higher growth rate is a marker for more growth hormones and other growth factors which while helping a person reach their peak potential height, also do a nice job of promoting too much cell growth. Uncontrolled cell growth is what cancer is after all.
Tall people also have more cells in their body, so more opportunities for a tumour to develop. And just like a giraffe with a long neck, tall people have longer intestines so more opportunities for exposure to cancer-promoting agents in the large intestine.
It is not all bad news though for the beanpoles amongst us. Being taller appears to be beneficial when it comes to preventing some other diseases such as diabetes, strokes and heart attacks.
Recommendations to live by
With colorectal cancer rates expected to rise worldwide, it is vital that people are aware that there are simple things they can do to help prevent the disease.
Swapping out some red and processed meat for fish or beans, or going for wholegrain rice instead of white rice are just a few tips for how people can work towards reducing their risk of colorectal cancer.
Keeping as healthy a weight as possible is not only important for preventing colorectal cancer, but also for reducing the risk of many other chronic diseases, including many other common cancers. And adding in some extra recreational activity will not only help with weight, but also have a host of other health benefits.
Bowel cancer may be one of the most common cancers seen in the Western world, but there is enough compelling evidence to show that by making healthy lifestyle changes, each person can significantly cut their risk.
What’s blue, round, sweet, grows on a bush and can boost your brain power? If you answered blueberries you would be correct. Or that should be: ‘mostly correct’. The ‘brain boosting power’ part needs a bit more science to catch up to the headlines, but it is looking promising that blueberries may be one food worthy of a ‘superfood’ title.
There is so much to be gained by having plenty of plant-based foods in your diet. While it may be tempting to stake your claim that health is all about the superfood du jour, it the variety of foods you eat that are key to good health.
Blueberries are one food that pop up regularly on ‘superfood’ lists. Long promoted for their brain-boosting power, is there much merit to the claims and should blueberries be a regular part of your diet?
Berries on the brain
The link between blueberries and the brain has grown out of observations that people who eat lots of fruits and vegetables over their lifetime have a lower risk of dementia. Scientists have singled in on one particular class of chemicals found in plant foods, called flavonoids, that may be the ‘active ingredient’ that could be protecting the brain from damage.
A collection of flavonoids called anthocyanidins have been getting even closer attention because of their antioxidant and anti-inflammatory properties. Anthocyanidins are abundant in berries and give these foods their bright blue, red and purple colours.
So how could the anthocyanidins in berries be of benefit for the brain? The high amounts of antioxidants in blueberries may be one way they help protect brain cells from damage. Berries also change the way that neurons in the brain communicate in pathways involved in inflammation and cell survival. Yet more research has shown that berries can also improve cognition, motor control and enhance neuroplasticity.
All about antioxidants
The antioxidant content of blueberries features front and centre to help explain their health benefits. While there is more to food than antioxidants, blueberries are certainly packed full of them as this graph below shows where the antioxidant content of a range of foods was measured and compared. Top marks for noticing that in the antioxidant superfood arms race, it is red kidney beans that you want more of in your belly. Perhaps with a blueberry dessert chaser.
Antioxidant capacity of foods measured using ORAC (oxygen radical absorbance capacity). Wu et al. 2004Blueberries boost the brain
An ageing population means a greater number of diseases linked to older age such as dementia. There is no certain way to prevent dementia, but scientists have been looking closer at the role that diet can play in reducing the risk of developing it and blueberries have attracted their interest.
One recent clinical trial that attracted a lot of media attention used a concentrated form of blueberry juice – high in anthocyanidins. The trial involved 26 healthy adults aged between 65 and 77. Half of the people drank concentrated blueberry juice each day for 12 weeks. The blueberry concentrate was equal to eating 230 grams of whole blueberries each day. The other half of the volunteers drank a placebo drink that had a blackcurrant taste, but no anthocyanidins in it.
The blueberry concentrate was equal to eating 230 grams of whole blueberries each day
After 12 weeks, people drinking the blueberry juice showed improvements in cognitive function, blood flow to the brain and activation of brain areas linked with cognitive function. There was also evidence suggesting an improvement in working memory too.
Blueberries may also have benefits for the brain by keeping it active during a mid-afternoon slump. In one study, volunteers who drank a blueberry smoothie in the morning did much better at mental tasks in the mid-afternoon than people who had a placebo drink. Again, it is likely the antioxidants in blueberries that stimulate the flow of blood and oxygen to the brain to help keep the mind fresh.
A heart health boost
Eating berries regularly is also linked to improved heart health. Berries can have a range of cardiovascular benefits from their anti-inflammatory, antihypertensive, hypoglycaemic and anticoagulant actions.
From a review of 22 randomised-controlled trials involving over 1200 people, regularly eating berries could significantly lower LDL-cholesterol, blood pressure, fasting glucose, body mass index (BMI) and glycosylated haemoglobin A1c (HbA1c). The cell signalling molecule involved in inflammation (tumour necrosis factor-α) also drops when people switch to eating more berries.
Fresh or frozen?
Fresh is great, but for convenience (and price) and when they are out of season, you can’t go past having frozen blueberries on hand. And as a bonus for choosing frozen, because they are processed and frozen soon after picking, the nutrient losses are small. In fact, a study from the Journal of Biomedicine and Biotechnology found that drying and freezing blueberries has no impact on the antioxidant activity of anthocyanin extracts.
Getting more blueberries in your diet
Here are some top tips to get more blueberries in your diet.
Add blueberries as your topping of choice to your favourite breakfast cereal
Sprinkle blueberries over green salad, or toss lettuce and sliced fresh fennel or celery with orange sections and blueberries, then drizzle with olive oil and vinegar
For an almost-instant blueberry sauce, microwave fresh, frozen or drained canned blueberries with a spoonful or two of your favourite jam. Serve warm over frozen yoghurt, sorbet or rice pudding
For a big blueberry hit, a smoothie is the way to go. Try 1/2 cup Greek yoghurt, 1/2 cup water, 1 cup of frozen berries, 1 banana and 1 teaspoon honey in a blender.
What it all means
An ageing population means a greater number of diseases linked to older age such as dementia. There is no certain way to prevent dementia, but scientists are looking closely at the role that diet can play in reducing the risk of developing it. Choosing a diet high in a variety of fruits and vegetables and including some delicious berries may go some way to reducing the risk of declining brain function in older age. And when it comes to blueberries, this is a case where the superfood hype may actually have a bit of solid science to support it.
Last week, a major study came out apparently calling into question current advice about carbohydrate and fat recommendations. The Internet and media organisations went into meltdown with claims that too many carbohydrates could be sending you to an early grave. Scrolling past the headlines (and actually reading the paper) gave a healthy dose of boring because what makes for a healthy diet has changed little.
Called the PURE (Prospective Urban Rural Epidemiology) study, this was a very large observational study looking at the link between fat and carbohydrate consumption and longevity in 18 countries across 5 continents. Running for 7 years and involving over 135,000 people, this was a very big study so its conclusions are right to take notice of.
The key finding from the work that attracted the most media attention was that a high carbohydrate diet was linked with a higher risk of earlier mortality, whereas total fat and individual types of fat were related to a lower risk of earlier mortality.
Digging deeper into the study, the research team found that global diets consisted of 61 percent energy coming from carbohydrates and 24 percent energy from fats. And while those in the highest carbohydrate consumption group (a whopping 77 percent of energy) had a higher risk of earlier death, it wasn’t cardiovascular disease they were dying from. What those other causes of death were exactly is unclear. Perhaps getting hit by a car running for a Mars Bar was one of them as a recent commenter on my Facebook page theorised.
A paradigm shift? Not quite
Does this study turn on its head ‘everything we knew about nutrition?’ Not quite. And here’s why.
Before the PURE study, there were many studies showing the opposite link between carbohydrates and longevity. So, when a conflicting study comes along, this grabs the media spotlight for the day.
Here is just one example – a major systematic review and meta-analysis from 2013 involving 17 individual studies and over 242,000 people showing a higher risk of earlier mortality as carbohydrate intake decreased. And this is the problem at times with observational research in that two studies can give polar opposite results so the findings of the PURE study should be seen through this filter.
I’m not going to pick apart the PURE study for its flaws. Such issues are consistent across all observational studies no matter if the conclusions support consensus views or not. What is of value to look at is the positive messages the study gave and how when you look at the full research field, it takes you back to some pretty sensible advice.
The PURE study was not so much an endorsement of low-carbohydrate diets, only a question mark on very high carbohydrate diets at a population level. Even the research team made this conclusion and when quoted in the press release for the study said:
“The best diets will include a balance of carbohydrates and fats – approximately 50-55 per cent carbohydrates and around 35 per cent total fat, including both saturated and unsaturated fats.”
A key shift in dietary habits over the last few decades has been towards an increase in consumption of highly refined carbohydrates and sugar which is at odds with what dietary guidelines actually recommend. It is possible that the PURE Study was detecting some of that change. Without knowing the overall diet quality of the participants, it is difficult to make firm conclusions.
In Australia, we sit at 43.5 percent energy from carbohydrate. We’re hardly killing ourselves slowly with a high carbohydrate diet at that level. But unfortunately, a lot of those carbohydrates are highly refined and we have too much added sugar in our diet. To add to this, only 6 percent of us eat enough vegetables each day.
The PURE study is interesting though as it shows how complex it is in determining the role of nutrition over many decades in improving health and simple measures of fat or carbohydrate quantity lose sight of the foods that are part of this. We eat foods, not nutrients, and as nutrition science advances, research is now turning to dietary patterns as being key predictors of health, rather than fixating on percentage targets for macronutrients.
Nutrition is a messy science
Nutrition science is messy. It is a young science and we have to deal with making conclusions from often imprecise research using well below par tools to measure dietary intake.
Here’s an example following of individual research studies that have been linked to either increasing or decreasing the risk of cancer. Green dots are good and show that the food lowers the risk; red dots are bad. Being selective in what dots you looked at and the studies you cite, red meat can lower your risk of cancer, but if you have it with onions, up goes your cancer risk!
Nutrition science is messy because it is impractical to run long-term, high-compliance randomised controlled trials (considered the ‘gold standard’) to answer big health questions. Good luck trying to get thousands of people to adhere to a particular type of diet for years on end – most people struggle for a week or two following a prescribed diet. So, we turn to the next best source of evidence and that’s observational studies. The PURE study is an example of an observational study.
Conflict of interest is also a problem. And I do not just mean ‘big food’ funding research. Researchers tied to a particular narrative with their research program (and maybe a large public and media following and the odd best-selling book or two) may find it difficult to do an about face when conflicting evidence presents itself. As humans, we are all susceptible to this. The scientific method helps reduce it, but it cannot eliminate it entirely.
Selective use of evidence (called cherry picking) can also be a problem. It has been said that you can build a case for any particular food or nutrient being good or bad for you by quoting a study or two that agrees with you. Just look at what happened when I did just that intentionally in making the case of why broccoli is toxic.
Take heart in the middle ground
But all is not lost. There are recurring themes that we can learn from in nutrition research and these are themes I have seen repeated year after year.
There are many paths to good health by eating a range of diets, with the biggest predictor of this being adhering to a dietary pattern that connects with a person, rather than following prescriptive advice. Low fat, high fat and somewhere in between like the Mediterranean diet can only be healthy if food quality of mostly plant-based minimally processed foods are put first.
Dietary patterns for the win
So what are the key nutrition themes seen in healthy dietary patterns around the world?
A major scientific review has taken things back to basics to reinforce where the best health gains are to be found with diet. A no small undertaking, the review looked at the diet and chronic disease links from 304 meta-analyses and systematic reviews published in the last 63 years. Type 2 diabetes, overweight and obesity, cancer and cardiovascular disease together accounted for most of the chronic disease links found. And here’s the summary:
Plant-based foods are more protective against the risk of chronic disease compared to animal-based foods
Wholegrain-based foods are slightly more protective than fruits and vegetables
Highly refined grains are deleterious to health
Dairy foods are neutral
Red and processed meat increases risk
Tea is the most protective beverage while soft-drinks the least
Eat more plant-based foods than animal foods, choose wholegrains over refined grains, limit red and processed meat and choose other beverages in preference to soft drink. And watch how much added sugar is creeping into your diet. Such recommendations may not get media attention like the PURE study, or help sell books in numbers like the latest popular diet, but they are the cornerstone of long-term good health.
Parents of children with autism often try diet changes or supplements to help improve the condition. A new review concludes that there is little solid evidence that any work.
In children with autism, a variety of gastrointestinal problems and associated symptoms have been often reported which has led to the popularising of a variety of dietary approaches to treat the condition. Wheat and dairy avoidance feature prominently as too do special elimination diets targeting food dyes and additives, yeast, simple sugars and naturally occurring salicylates in foods.
Concerns have been raised about the lack of solid evidence for any special ‘autism diet’. This is an area where personal anecdotes abound to support many of the popular autism diets rather than good science. Nutritional deficiencies are a risk in some of the stricter elimination diets. This is a concern considering the nutritional needs of the growing child so they should not be endorsed and adopted if they may not be giving a therapeutic benefit to most children.
So what does the scientific evidence say about autism diets when tested in a clinical trial? A new review based on 19 clinical trials looked at the benefits of special diets or supplements on autism symptoms. Gluten-free and casein-free diets, digestive supplements, methyl B12 and omega-3 fish oil supplements were the most common treatments tested.
There was no solid evidence than any of the treatments made a significant difference in children with autism. Where there were some positive effects, there was not enough consistent evidence to make a firm conclusion. And in some of the trials, children given a placebo showed greater improvements than those taking omega-3 supplements. Most trials were small in size and of short duration, further making it difficult to offer a firm conclusion either way about the benefit or not of the treatments.
What it all means
It is plausible that certain dietary interventions for autism could benefit some children, but not others, but there is no way to know who these children are short of parents going on a merry-go-round of trialling a multitude of treatments. Parents deserve to know if a treatment they are being recommended has sufficient evidence for a benefit. Children with autism are already picky eaters, so it is vital to consider the nutritional impact of any change in the child’s diet. If parents do opt for some form of dietary modification for their child, particularly overly restrictive ones, then professional supervision is recommended to prevent nutritional deficiencies.
Eating well is an important part of reducing a person’s risk of cancer. When it comes to dietary choices for people who have survived cancer, key themes surface showing that a healthy diet is just as important.
Thanks though to earlier detection and improved treatments, more and more people are surviving a cancer diagnosis and going on to live long lives. Well-supported diet and lifestyle recommendations are already in place showing the way for how a person can lower their risk of developing cancer. Much less evidence exists though to make clear recommendations for diet advice for cancer survivors.
Looking at studies that surveyed the diet and lifestyle habits of cancer survivors finds a sparse research field. Only a few key cancers have been studied and results can appear contradictory. Further complicating things, some studies only looked at pre-diagnosis diet while others examined post-diagnosis diet.
With the mixed research field of diet among cancer survivors, a German research team collated together 117 studies involving over 200,000 cancer survivors into a single meta-analysis. What they found was perhaps not too surprising.
Eating lots of vegetables and fish had a favourable link with longer survival. Alcohol was linked with a worse outlook.
Grouping together whole diets found that one type of diet stood out. Termed wholefoods, prudent or healthy depending on the study, a common theme was a dietary pattern high in fruit and vegetables and wholegrains, but low in red processed meat, refined grains and high-fat foods. Eating close to this style of dietary pattern was linked to a 22 percent lower risk of earlier death from cancer.
The opposite of a healthy diet was labelled a Western diet, high-fat diet, high-sugar snacks diet or simply: an unhealthy diet. Made up of processed meat, refined grains and lots of added sugar, this diet was linked with a 50 percent higher mortality risk from cancer compared to similar people following a healthier diet.
What it all means
Greater numbers of people are surviving cancer. With more survivors comes a greater focus on research that spotlights key lifestyle choices that raise survival odds even higher. Dietary patterns that are closely connected to foods near to their natural state such as fruits, vegetables, fish and wholegrains currently sit at the top of evidence recommendation for people with cancer to be steered towards.
It’s a simple question which has stumped obesity researchers for decades: why do most people who diet to lose weight, regain it? A drop in metabolism gets the most blame, but the hidden culprit could simply be an increase in appetite.
Losing weight is easy; keeping the weight off is the hard part. No need to cite scientific studies to support that claim with decades of failed dieting attempts endemic in the population. All the popular diet trends can lead to weight loss, but only a tiny minority of people maintain their weight loss long-term.
One of the key explanations for weight regain is a drop in resting metabolism. A slower metabolism makes it more likely that even with less food eaten, it can still exceed a person’s needs. There is merit to this idea, but it probably does not explain the whole picture.
Looking at metabolism and energy expenditure is only half of the equation. The other half is having an accurate fix on just how much food a person eats, even when restricting calories. Measuring how much someone eats is hard to study in controlled research. A person’s food intake changes substantially from day-to-day, and we don’t have many accurate methods to track this in a free-living situation.
Weight regain explained
A year-long clinical trial with a new drug for treating diabetes gave researchers an opportunity to see how food intake can change with weight loss. The drug used in the trial was canagliflozin. The drug works by causing more glucose to be lost in the urine. Losing excess glucose in the urine also means a loss of a potential energy source. The favourable side-effect is weight loss.
A total of 153 people with type 2 diabetes took canagliflozin for 1 year. For a comparison group, 89 people took a placebo pill. Both groups lost weight, but it was around 3 kilograms in the drug treatment group and just 1 kilogram in the placebo group.
A puzzling question was why the drug-treatment group hadn’t lost more weight. From laboratory tests, the amount of energy lost in the urine from excreted glucose was about 1500 kJ (360 Calories) per day. Even with this degree of lost kilojoules from the body, weight loss plateaued.
What explains the weight loss plateau? The research team burrowed into mathematical models of how body weight and energy intake are related. And the answer they came up with? Appetite.
People in the drug treatment group were hungrier. The hunger drove them enough to eat around 420 kilojoules (100 Calories) extra each day for every kilogram of weight they lost.
Even though people in the study didn’t know how many kilojoules the drug was limiting each day by excretion, their bodies fought against the weight loss, prompting them to eat more to make up the deficit.
The influence of appetite is three times stronger than the slowing of metabolism from weight loss. Add the two together and it makes it almost inevitable that lost weight will be regained.
A clear downside to the study was that it was only done in people with type 2 diabetes using a specialist drug where weight loss was more a side-effect. How appetite changes may play out in healthy people is unclear.
What it all means
The research helps to explain that weight regain is not a simple matter of poor self-control. You can ignore hunger cues for a time, but they persist while the body remains in a transient state of weight loss. Taking the focus off ‘the best way to lose weight’ and more onto helping and support a person maintain weight loss, or even just keep their current weight stable and instead focus on their health, is where effective therapies for weight loss need to be going.
Telomeres are the protective cap at the end of DNA which protects our chromosomes. The length of telomeres shortens with age which raises the intriguing possibility that telomere length forms a key part of the ageing process. Now scientists are looking into how much diet can influence telomere length.
Telomeres are one of today’s hottest topics in science. Top researchers are connecting telomeres to ageing, health and even longevity. The claims make for great headlines, but also brands the field a controversial one for it.
What exactly are telomeres? They’re the caps at the end of each strand of DNA and act as protection for our chromosomes. Think of them like the plastic tips at the end of shoelaces. As we age, telomeres become shorter and contain less coating. With the protective cap compromised, DNA strands become damaged. Think of how your shoelace can become frayed when it loses its plastic tip.
Each time a cell divides, the telomeres shorten. A nice analogy is that telomeres are like a bomb fuse: when they get to a critical length, it’s kaboom!
Pharmaceutical companies are desperately searching for drugs that can slow down the shortening of telomeres and protect DNA from the ravages of time. A drug that could do this would rake in big money. It’s a modern-day search for the fountain of youth. Putting aside the headline grabbing sound bites of a ‘longevity pill’, what do we know already about how lifestyle can influence the rate of telomere shortening?
Inflammation key to telomere length
Inflammation and oxidative stress are two factors connected to faster rates of telomere shortening. Insulin resistance, a key part of metabolic diseases such as type 2 diabetes, also elevates inflammation and oxidative stress. Diet and lifestyle are big players in chronic inflammation. This opens the door for a connection between diet influencing telomere length and now we have some research to fill this void.
In the first study of its kind, researchers looked at studies that collected information on both dietary habits and telomere length of participants. From a pool of 17 studies, several themes emerged. A Mediterranean-style dietary pattern and also diets high in fruits and vegetables were linked to longer telomere length. On the opposite end, diets high in highly refined grains, processed meats, and sugar-sweetened beverages were pointing towards a shorter telomere length.
The quality of the research studies that informed the conclusion were quite mixed. Most of the studies were cross-sectional. A cross-sectional study only gives a snapshot at a moment in time of diet and telomere length. Sturdier studies would measure diet and telomere length repeatedly over a span of many years.
Making sense of it all
How to make practical sense of this new research? Let’s start with what we do know. Dietary patterns rich in fruits, vegetables and wholegrains are linked with less chronic diseases and a longer life. On the opposing side, we have the hype and hope of telomere length being the cup to drink out of the fountain of youth.
The rope bridge that connects diet with telomeres is intertwined with inflammation and oxidation. If you eat a poor diet: the strands of the rope bridge fray and the bridge crashes down well before its time. Good diet: a strong bridge capable of bearing the load of what life throws at it.
Let’s propose that telomere length turns out to be a deadend alley in the search for the cause of ageing and disease. The implications for dietary recommendations don’t budge one bit. There is so much known already about the key dietary patterns linked to good health. No need to tie your shoelaces in knots trying to figure out ‘why’, just eat and enjoy.
Eating fruits and vegetables are good for your health in so many different ways. Now in the first major scientific study of its kind, eating more of these powerhouse foods has been linked to substantial increases in people’s happiness levels.
Fruits and vegetables have an abundance of health benefits. But it’s not from lack of scientific evidence for their benefit that explains why we don’t eat enough of these foods. In Australia, just 6 percent of people eat the recommended amount of vegetables each day. For fruit, only half eat the recommended number of serves.
In the search for perhaps a different angle to promote the health benefits of fruits and vegetables, researchers are looking at their link with psychological health. Previous research has found some interesting associations with fruit and vegetable consumption and improved psychological health. But what is lacking is a large-scale study to really solidify this link.
Using a large sample of more than 12,000 randomly selected people in Australia, researchers were able to track their diet, health, happiness, life satisfactions and well-being from 2009 to 2013.
The key to happiness?
So what was the key finding? Happiness, life satisfaction and well-being all went up for each extra daily portion of fruits and vegetables eaten. And this was after making allowance for people’s changing incomes and personal circumstances. The happiness health links reached a peak at eight servings a day of fruits and vegetables. The improvements in mental health were seen within 24 months of increasing the amount of fruits and vegetables eaten.
The research team took it one step further and compared the mental health improvements to life changing situations. For someone going from eating no fruits and vegetables to eating eight portions a day, they could experience an increase in life satisfaction equivalent to moving from unemployment to employment.
Finally the researchers looked at the effect of a pro-active fruit and vegetable consumption campaign on dietary habits. Here they found a link between the intensity of the campaign, its outcomes in people eating more fruit and veg, and positive mental health benefits.
A challenge in getting a person to want to eat more healthy food is that health benefits may take decades to materialise. That green salad today may (or may not) mean a lower risk of cancer in 30 years. On that time-scale, the mental health benefits linked to eating more fruits and vegetables are closer to immediate. And improved mental health would help to reinforce the positive dietary change.
There are likely many reasons to explain a link between eating more fruits and vegetables and well-being. Higher levels of antioxidants is one possibility. Then there is the role of fibre in supporting a healthy population of gut bacteria. Gut fermentation products can act directly on the brain, potentially altering mood and behaviour.
What it all means
Diet and mental health is a rapidly growing research field. We can expect more research to come to light linking the benefits of plant-based foods with improved mental health. Rather than long-term, less immediate benefits, future health campaigns will have a new angle to focus on. Who doesn’t want to feel happier?