A review of the week’s plant-based nutrition news March 28th 2020
Another week and now in full lock-down in the UK. I hope you are all staying safe and that this review provides some distraction from the current challenges.
SOYA AND HEART HEALTH — NEW STUDY REPORTS BENEFITS: Soya is full of healthy nutrients, including being a source of ‘complete’ protein (all 9 essential amino acids present), fibre, omega-3 fats and calcium. Soya also contains isoflavones, plant oestrogens, which have often led to controversy with regards to health effects.
This large study included >200,000 men and women from 3 US cohort studies — Nurses’ Health Study and Health Professionals Follow-up Study — that have been followed since the 1970’s and 80’s. Dietary soya consumption was analyzed — mainly tofu and soya milk — and the isoflavone content of the diet calculated. The results showed that there was a linear relationship between the consumption of isoflavones and risk of coronary heart disease. Those with the highest intake had a 13% reduction in risk of heart disease compared to the lowest intake, after adjusting for other healthy lifestyle factors.
Tofu intake was also associated with a reduced risk of heart disease. Those eating tofu 1 or more times per week had a 18% reduced risk of heart disease compared to those that rarely ate tofu. Every one serving per week reduced the risk by 9%. In women the association was only significant in premenopausal women and postmenopausal women NOT on hormone therapy. Hormone therapy appeared to neutralize the effects of tofu consumption.
Soya milk consumption did not impact heart health but this might have been because overall soya milk consumption was low in the cohorts.
What are the potential mechanisms? Isoflavones and soya has been associated with better endothelial function, have anti-oxidant and anti-inflammatory effects, reduce blood cholesterol and the level of oxidized-LDL and have beneficial effects on the gut microbiome.
In conclusion: although not every study has shown this benefit, soya consumption may be beneficial for heart health. It contains several health promoting nutrients and should be part of a healthy plant-based diet. In addition, soya consumption can benefit those with menopausal symptoms, reduce the risk of breast and prostate cancer and improve bone health. Here is a review paper on soya. Soya is also an excellent food to incorporate into the diet of babies and children and we have a factsheet that you can download from the website.
THE IMPACT OF VEGAN AND VEGETARIAN DIETS ON THE GUT MICROBIOME: The trillions of organisms in our gut making up the microbiome represent an body organ in itself. We understand most about the bacteria living in the gut and these bacteria use nutrients from foods, release harmful or beneficial metabolites and regulates the immune system. Dysbiosis, microbial imbalance or maladaptation, has been associated with an increased risk of chronic disease. Lifestyle factors impact the health of the gut microbiome and previous studies have shown that diets high in whole plant foods, including vegan and vegetarian diets, promote enrichment of fibre-degrading bacteria and higher levels of faecal short-chain fatty acids (SCFA), which are associated with better health and a more robust immune system. A diet low in whole plant foods results in increased levels of trimethylamine oxide, a potential risk factor for cardiovascular disease, renal failure and type 2 diabetes. Therefore, modulation of the gut microbiome has the potential to improve health and reduce the risk of chronic disease.
The study highlighted included 30 healthy adult volunteers in Italy who had been following an omnivorous (n=10), an ovo-lacto-vegetarian (n=10) or a vegan diet (n=10) for at least one year. Faecal samples were collected on the same day of three consecutive weeks, and the three samples were pooled before microbiome, metaproteome and metabolome analyses. Food and beverage intake was estimated by means of a 7-day weighed food diary, which was completed every day for a total of one week. The study used a multi-omics approach to analyse the bacterial genes and proteins present in the faecal sample.
The results are complicated! They showed that genes responsible for amino acid and carbohydrate metabolism, chemotaxis (for movement of the organism) and flagellar assembly (helically shaped structures containing the protein flagellin and involved in movement) were associated with a vegan/vegetarian diet. In addition, the analysis showed; statistically significant differences in the synthesis of 181 proteins, mainly responsible for carbohydrate, nitrogen and cofactor and vitamin metabolism between the vegan/vegetarian vs omnivore diets; more abundant proteins responsible for DNA replication and repair in those on vegan/vegetarian diets; a higher concentrations of SCFA (acetate, butyrate and propionate) in those on vegan/vegetarian diets; proteins related to amino acids and nitrogen metabolism differed between the diet groups.
So what does this actually mean for health? The results suggests that the microbiomes of individuals eating plant-based diets, which are rich in fibre, are better able to utilise the nutrients in the diet, have a higher production of SCFA’s and do not produced trimethylamine. This has the potential to benefit health by enhancing the activity of the immune system, maintain the integrity of the gut lining, suppressing tumour growth and reducing compounds associated with the development of atherosclerosis. We already know that the gut bacteria are important in making and activating vitamins. For example, vitamin A is metabolised in the gut to its active form retinoic acid, which is essential for a healthy immune system and for fighting infection. Vitamin K2 is produced by gut bacteria although the impact on health of this vitamin is still not well defined but thought to be important for heart and bone health.
The author’s conclusions; ‘our data demonstrated how responses from the intestinal microbiome to vegetable-rich diets primarily include: an increased cell motility to access nutrients, an increased catalytic activities for carbohydrates and food proteins, the synthesis/release of bioactive metabolites/proteins and potentially beneficial impacts on human health’
An excellent way to enhance the health of the gut microbiome is to incorporate fermented foods into the daily diet. These include sauerkraut, kimchi, pickled vegetables, kombucha, water kefir, tempeh, sourdough bread, miso and plant-based yogurts with live cultures.
VEGAN DIET AND EFFECTS ON BLOOD CELLS AND AMINO ACIDS: This is a randomised study of vegans — a rare thing! We have known for a while that our diet can either promote or reduce inflammation. Obviously its preferable to consume an anti-inflammatory diet and there is a relatively recent dietary score — called the dietary inflammatory index — that allows researchers to score foods within the diet based on their ability to cause inflammation. It is not surprising to learn that plant-based foods are ranked as anti-inflammatory and red/processed meat, processed foods and sodas ranked as pro-inflammatory. The less inflammatory the diet, the lower the risk of chronic disease because chronic inflammation is the unifying mechanism involved in most common illnesses.
This study randomised 53 healthy, omnivore subjects to a vegan diet (n=26) or meat-based diet (n=27) for 4 weeks following a pre-treatment phase of a one week controlled mixed diet. The effect of the diet on inflammatory and immunological markers relevant particularly to rheumatoid arthritis were studied. The vegan diet was found to significantly reduce levels of neutrophils, monocytes, and platelets (but not lymphocytes) when compared to the omnivore diet. This was associated with a fall in the level of GM-CSF (granulocytes-monocyte colony stimulating factor), the cytokine involved in boosting levels of neutrophils and monocytes. In addition, the vegan diet lowered levels of branched chain amino acids (BCAA — 3 essential amino acids, leucine, isoleucine and valine). There was no difference between diets groups in a number of other tests, including IgG glycosylation patterns, light chain levels, CRP or percentage of regulatory T cells.
This study adds to already published evidence suggesting that a vegan and vegetarian diet can reduce inflammation. There have also been some small studies that have demonstrated the potential for a vegetarian/vegan diet for treatment of conditions such as rheumatoid arthritis. One such study, a single-blind controlled study in 27 patients with rheumatoid arthritis, used a protocol of fasting for 7–10 days, then consuming an individually adjusted, gluten-free, vegan diet for 3.5 months, and then consuming an individually adjusted lacto-vegetarian diet for 9 months. The results showed that patients derived clinical benefit from this protocol compared to the control group and there was a significant reduction in markers of inflammation, specifically white cell count and CRP.
The largest study ever conducted to examine hematological parameters by degrees of animal food consumption in >450,000 white British and British Indian individuals found that vegans, but not vegetarians, had a lower platelet count and Caucasians consuming low quantities or no meat had lower white cell counts, all adding to the evidence for lower levels of inflammation.
Regarding BCCAs, levels are influenced by diet with plant-based diets resulting in lower circulating levels. This is considered beneficial given that higher levels are associated with an increased risk of type 2 diabetes, may adversely effect kidney health and BCAA metabolic pathways may be implicated cancer growth and survival. Thus a diet that provides lower levels of BCAAs is considered beneficial.
REDUCING RISK OF CANCER THROUGH INTENTIONAL WEIGHT LOSS: Obesity is now the second commonest cause of cancer after tobacco smoking. This study provides hope. It reports finding from the The Women’s Health Initiative Observational Study. 58 667 post menopausal women aged 50–79 years had body weight and waist circumference measured at baseline and 3 years later. A change in weight or waist circumference was categorized as stable if < 5%, loss if >5%, and gain if >5%. Participants were followed for a mean of 12 years during which time 6033 obesity-related cancers (breast, ovary, endometrium, colon and rectum, esophagus, kidney, liver, multiple myeloma, pancreas, stomach, and thyroid) occurred.
Compared to those with stable weight, women who intentionally lost weight or reduced their waist circumference reduced their risk of cancer by 12%. The greatest impact was on the risk of endometrial cancer and colo-rectal cancer.
So, the risk of cancer is not fixed and can be altered by addressing risk factors. We know that people who stop smoking can significantly reduce their risk of lung cancer although it does not seem to return to that of a never-smoker. In the same way, this study highlights that intentional weight loss can reduce the risk of cancer. What is the best way to lose weight? Diet is the main lifestyle determinate of body weight although we do know that the causes of obesity are multi-factorial and complex. Vegan and vegetarians have a lower BMI than meat eaters, those that eat the most whole plant foods gain less weight over time and a whole food plant based diet is one of the most effective ways to achieve sustainable weight loss.
NUTRITION AND ASTHMA: This paper provides an up to date review on the topic of nutrition and asthma. Well worth reading. A summary of the findings include;
- Higher intakes of fruits and vegetables can reduce the risk of developing asthma and improve the control of asthma in those with an established diagnosis.
- Dairy consumption is associated with an increased risk of developing asthma and can exacerbate the symptoms of asthma in those with an established diagnosis.
- A Western-diet pattern high in saturated fat and low in fibre has been associated with a greater severity of asthma.
- Plant-based diet patterns such as Mediterranean diet can reduce symptoms.
- Mechanisms by which plant foods can reduce asthma risk and severity include higher consumption of fibre, antioxidants, unsaturated fatty acids and lower intake of saturated fats, which all help to reduce inflammation in general but also airway inflammation. Improved health of the gut microbiome and hence immune system. Maintenance of a more healthy body weight which is associated with a lower risk of asthma.
- Vitamin D deficiency may play a role in increasing the risk of asthma.
- Large scale randomised studies are still required to truly understand the potential of a dietary intervention on the risk and severity of asthma.
NEW DIETARY GUIDELINES FOR PATIENTS WITH INFLAMMATORY BOWEL DISEASE (IBD): It has always been suspected that diet plays a role in the development of IBD. Patients report changes in symptoms based on dietary exposures and various small-scale intervention studies have reported benefit with diet changes. However, there has not been a consistent recommendation from the gastroenterology community, with patients reporting that the medical profession in general ignore the potential of diet as a therapeutic intervention when in fact it is the first and foremost question in their minds. This new guideline is therefore welcome and helps address the evidence on diet and IBD. The aim of the guideline was to provide help to patients with established IBD to understand the role of diet in the disease.
The panel of experts reviewed evidence on 7 food groups, dietary components, and 5 food additives. These included dairy, red meat, processed meat, poultry, eggs, fruits and vegetables, fat, refined sugar, wheat and gluten, alcohol, emulsifiers, maltodextrins and artificial sweeteners, gums and thickening agents, and nanoparticles. A thorough review of of the available literature from human and animal studies was conducted. Ulcerative colitis (UC) and Crohn’s disease (CD) were considered separately.
‘Evidence level (EL) supporting the recommendation was categorized loosely based on the following scale: randomized controlled trials (RCTs) provide high-level evidence, observational studies in humans provide low-level evidence, and everything else is very-low-level evidence. Level of evidence could be increased or decreased based on the strength of association and reproducibility of findings, or quality of studies’.
The recommendations are all very cautious in my view (currently published as an uncorrected proof). The findings are summarised in the figures below taken from the paper. The main take home message is in line with healthy eating guidelines in general i.e. fruit and vegetable intake should be increased, red and processed meat consumption should be reduced, saturated fat should be replaced by sources of unsaturated fat and food additives and emulsifiers (found in processed foods) should be avoided.
What we do know is that semi-vegetarian, vegetarian and vegan diets have been reported in small studies and case reports as effective in treating IBD. Japanese researchers have been the pioneers in this field of research. Plant-based diets help to address the key mechanisms driving IBD as illustrated in the graphic below from this excellent review paper. This includes gut dysbiosis (abnormal gut microbiome), gut epithelial injury and inflammation.
Our very own PBHP UK board member Dr Alan Desmond has also published a case of CD treated with a plant-based diet, which you can read here.
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