Research & Policy Update: 25/02/21

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» Research & Policy Update: 25/02/21

In this edition of Research & Policy Update, RAC member, Dr Shireen Kassam updates us on the Mediterranean versus vegan diet study; coffee and prostate cancer; supplements for cardiovascular disease; vegan diets for children and controversy from the PURE study.

THE MEDITERRANEAN DIET VS VEGAN DIET: This is a unique study that compared the conventional Mediterranean diet with a low-fat vegan diet (whole food plant-based, no added fat). 62 overweight adults were randomised to either a Mediterranean diet or a vegan diet for 16 weeks. After a 4 week washout period in which participants returned to their baseline diet, they then crossed over to the alternate diet for a further 16 weeks. Both groups could eat as much as they wanted. The Mediterranean diet was executed as per the well known PREDIMED study and included 50g of olive oil daily. The vegan diet was intended to be approx 75% carbs, 15% protein and 10% fat from whole plant sources, no added oil and a B12 supplement. Bodyweight, blood pressure, body composition, insulin resistance and glucose tolerance were measured before and after each phase.

What were the results? The actual fat intake was 43% of calories in the Mediterranean group and 17% in the vegan group. Although participants could eat as much as they wanted, the vegan group consumed around 500 fewer calories per day. The vegan group also had a higher intake of fibre and lower intakes of saturated fat and cholesterol. The vegan group lost an average of 6kg but the Mediterranean group lost no weight. The vegan group also had significant reductions in body fat and visceral fat. The vegan group improved blood total and LDL-cholesterol levels and insulin sensitivity with no change in the Mediterranean group. Both groups had reductions in BP but a greater effect in the Mediterranean group. The Mediterranean group also had a greater reduction in triglyceride levels whereas the vegan group did not, although this did not reach statistical significance

So all in all the vegan diet held its own against the Mediterranean diet with certainly more going in its favour in this comparison and certainly better for weight loss. The authors hypothesise that the greater reduction in BP in the Med group may have been due to more consumption of vitamin E in olive oil and its anti-oxidant function. Dairy, which is included in the Mediterranean diet may have a BP-lowering effect. It may have also been related to the nut consumption in the Mediterranean group. I wonder how the vegan diet would have fared with a daily tablespoon of flaxseed added?

This study is so far one of a kind as previous comparisons of a veg/vegan diet with the Mediterranean diet have not been whole food or low fat. The Mediterranean diet has been compared with a vegetarian diet in a randomised study. The CARDIVEG study randomised 118 overweight participants with high blood lipids or glucose, but who were not on any medication, to either one of the two diet patterns. It was a 3-month intervention with both diet groups having the same but reduced calorie intake. Both diets were effective in reducing body weight, body mass index, and fat mass, with no significant differences between them. There was no significant change between groups in glucose and insulin levels and measures of insulin resistance. However, the vegetarian diet was more effective in reducing low-density lipoprotein cholesterol levels, whereas the Mediterranean diet led to a greater reduction in triglyceride levels.

In a very small study comparing the vegan diet to the Mediterranean diet for cardiovascular health in young, healthy volunteers, the Mediterranean diet led to improvements in microvascular function and the vegan diet led to a greater reduction in total cholesterol and weight loss. It is worth noting that the vegan diet in this study was not a low-fat intervention with participants consuming 35% of calories from fat.

There is lots of detail in the current paper so do read as it’s open access. All in all a pretty reassuring study supporting a low fat vegan dietary approach albeit in the short term. I would like to see a follow-up study of a healthy vegan diet with extra virgin olive oil, flaxseeds or nuts or all three!

GOOD NEWS FOR COFFEE LOVERS: Although not necessary in the diet, coffee consumption does seem to have some benefits for health for those that enjoy it. Regarding cancer, there is consistent evidence for a reduction in the risk of liver and colorectal cancer. This paper examines the impact of coffee consumption on the risk of prostate cancer

The study included data from 16 prospective cohort studies with 57,732 cases of prostate cancer and 1,081586 participants. Compared to those drinking the least, those drinking the most had a 9% reduction in risk of prostate cancer. In the dose-response analysis, a reduction in the risk of prostate cancer of nearly 1% was observed for each increment of one cup of coffee per day.

There are a number of possible reasons for these finding that the authors discuss. Caffeine, caffeic acid and chlorogenic acid in coffee may be responsible for this benefit. These compounds have been shown to improve insulin sensitivity, decrease insulin and insulin-like growth factor levels and increase levels of sex hormone-binding globulin and testosterone. These compounds also have anti-oxidant and anti-inflammatory properties.

Clearly, such a study merely confirms an association rather than a causal relationship, nonetheless, for those that enjoy drinking coffee, there may be benefits to health too. An umbrella study from 2017 including 201 separate meta-analyses demonstrated that coffee consumption was more often associated with benefit than harm for a range of health outcomes. These benefits included a reduced risk of death, CVD, certain cancers (prostate, liver, endometrial, melanoma and non-melanoma skin cancer, oral cancer and leukaemia), Parkinson and Alzheimer disease and type 2 diabetes. The only cautionary note was the finding of increased risk of fracture in women but not men and adverse pregnancy outcomes. So avoidance of coffee consumption during pregnancy is definitely advisable. Of course, what coffee is consumed with is likely to be important and adding any form of dairy, be it milk or cream, is not advised given the strong association with increased prostate cancer risk.

SUPPLEMENTS FOR PREVENTION AND TREATMENT OF CARDIOVASCULAR DISEASE (CVD): This paper reviews data since the 2018 systematic review and meta-analysis of randomised controlled trials and includes data from 156 trials. Data are provided for the 4 common supplements taken (multivitamins, vitamin D, calcium, and vitamin C), antioxidants, folic acid, B-complex, and niacin (vitamin B3). The term“multivitamin” has been used to describe the use of supplements that include most vitamins and minerals such as the brand Centrum. In addition, the study included B-complex vitamins (a combination of 2 or more of the following: B6, B10 [folic acid], B12) and antioxidant mixtures (a combination of 2 or more of the following: vitamins A, C, E, beta-carotene, selenium, zinc) as combined entities.

Multivitamins, vitamin D, calcium, and vitamin C did not have a significant effect on CVD outcomes. Folic acid and B-complex vitamins reduced the risk of stroke. Folic acid supplementation studied in 7 trials reduced the risk of stroke by 21% and the reduction in total CVD was found at a dose of 0.8mg/d. B-complex vitamins reduced the risk of stroke in 9 of 12 studies. Niacin was associated with a 10% increased all-cause mortality. Antioxidant supplements did not show a benefit.

Regarding folic acid supplementation, the authors note that this benefit was mainly seen from data from a large study conducted in China where, in contrast to the US, food is not fortified with folic acid. However, the authors state ‘However, folate levels can also be raised by consumption of leafy vegetables and wholegrain cereals (in addition to the consumption of fortified white four products), and the consumption of folates from food may have advantages over the synthetic folic acid used in supplements that may be associated with higher prostate cancer risk…and colon cancer risk’. B-complex mixtures of folic acid, B12, and B6 have been used to treat high homocysteine levels associated with stroke. The current meta-analysis showed a 10% reduction in the risk of stroke in this context (NNT = 201).

The conclusion: ‘In the absence of very clear micronutrient health benefits and with concerns that excess consumption of certain micronutrients may have undesirable consequences, it appears that more certain CVD gains can be achieved by dietary change that follows the move to more plant-based diets, as advised now internationally.’

INSTEAD OF A SUPPLEMENT, CUT OUT REFINED GRAINS FOR BETTER CARDIOVASCULAR HEALTH: The Prospective Urban and Rural Epidemiology (PURE) study has provided quite a lot of controversy. It is a large prospective cohort study that stands apart from others by spanning 21 countries covering high, middle and low-income countries. One of the first publications suggested that eating diets high in carbohydrates were associated with worse health outcomes when compared to a diet high in fat, including saturated fat. Many well-respected researchers have criticised the study results. So what does this new study add?

This report included data on 13,730 participants followed for a median of 9.5 years. The primary outcomes examined were a combination of total mortality and major cardiovascular events (defined as death from cardiovascular causes, nonfatal myocardial infarction, stroke, or heart failure). In the time period, 10.3% of participants met the primary outcome with over a third of these deaths due to CVD. The association of these outcomes were correlated with whole grain, refined grain and white rice consumption. Refined grains were classified as wheat grain products or flour that had the bran and germ layer removed. Consumption of refined grains was highest in South East Asian and white rice in South Asia. Countries in Africa consumed the most whole grains.

The results showed that compared to people eating the least refined grains (<50g/day), those eating the most (>350g/d) had a significant 28% increased risk of dying or having a CVD event. For every 50g increase in consumption of refined grains, there was a 2% increase in the risk of death or CVD event. The consumption of whole grains and white rice were found to be neutral — neither good nor bad for the outcomes examined.

So does this study tell us anything new? I don’t think anyone is going to be surprised to learn that refined grains are unhealthy. However, when you delve into the results of this study, the negative outcomes for refined grain consumption was only found in China, which comprised a third of the participants in this study. Sadly, I suspect this more reflects the fact that China has increasingly transitioned to a Western diet high in meat, sugar and refined grains, with falling consumption of whole plant foods. The neutral results for whole-grain consumption are surprising given that previous studies show significant numerous benefits for health. However, the most whole-grain consumption was in Africa where socioeconomic factors likely play a larger role in health outcomes and are likely confounders in this study analysis. In high incomes countries, whole grain consumption is less prevalent but there is also much better access to healthcare services.

So overall, I am not sure this study was worthy of the BMJ or tells us anything we didn’t know, other than casting doubt over the health-promoting effects of whole grains.

VEGAN DIETS IN CHILDREN: This study caught the attention of the media which is not surprising given that the title immediately suggests that a vegan diet may not provide adequate nutrition in children. So what did the study really show?

This cross-sectional study from Finland included 40 children with a median age of 3.5 years (range 1–7) who were following either a vegan, vegetarian or omnivorous diet. Participants were recruited through daycares that were also providing vegan meals. Those following a vegan diet had done so from birth, but note there were only 6 vegan children included! Dietary intake was calculated from an estimated 4-day food record filled in by the parents and daycare personnel between May and October 2017. Data on height and weight were collected as were blood and urine samples. The lab tests included lipid profiles, inflammatory markers, cholesterol intermediates, amino acid and fatty acid profiles.

The results? The vegan children had lower saturated fat and protein intake (but still adequate), negligible cholesterol intake and no intake of long-chain omega-3 fatty acids — DHA/EPA. They had higher intakes of unsaturated fat, linoleic acid, alpha-linolenic acid, fibre, iron, zinc and folate. There were no differences in vitamin A and D intake. Height and weight measurements were similar across all diet groups. The vegan children had significantly lower blood levels of total, LDL and HDL cholesterol. Of note, the only children with high LDL-cholesterol levels were omnivores. Tests also showed that serum concentrations of transthyretin and retinol-binding protein (both measures of vitamin A status) and vitamin D, were lower in vegans than in omnivores but no differences in ferritin, zinc or urine iodine levels. Vegan children were virtually all supplementing with vitamin B12, iodine and vitamin D. Bile acid synthesis was found to be different in vegans compared to omnivores with higher steady-state levels of unconjugated primary bile acids. There were lower levels of certain essential amino acids, particularly branched-chain amino acids (BCAA). There were also differences in fatty acid metabolites in the serum.

I am not sure why the conclusions from the authors and those reported in the media are quite so negative. The study included only 6 vegan children! Transthyretin and retinol-binding protein levels were lower but not deficient and actually vitamin A status was not shown to be deficient. Carotenoids, precursors of vitamin A, are abundant in a plant-based diet and vitamin A status has never been a major concern with a healthy plant-based diet. Low cholesterol levels are surely a good thing especially since we know that high levels in childhood predict an increased risk of heart disease. I discussed a relevant paper just recently. There is no evidence to suggest that lower levels of BCCAs (leucine, isoleucine, valine) are harmful. It’s more likely that this could be beneficial as BCAA’s are implicated in insulin resistance. In fact, when you administer BCAAs to vegans, insulin sensitivity decreases! I accept the low levels of DHA/EPA may be a concern but we just don’t know this for sure. To be safe, DHA/EPA can be obtained from algae for those on a plant-based diet.

Of note, the VeChi study that is following a larger group of German children who have been vegan from birth have not reported any adverse outcomes for vegan children to date.

THE GRETA THURNBERG EFFECT: I try and cover an aspect of climate health each week. It’s truly remarkable to have a paper published about the impact of an individual activist on engagement in climate activism. This paper examined the impact of Greta’s activism on 1303 US adults. In summary, those that had heard of Greta, her work and her message, were more likely to have greater intentions of taking collective actions to reduce global warming. These individuals were also more likely to believe that ‘by working together with like-minded others, they can reduce global warming'. These individuals were more likely to align with liberal rather than conservative political ideologies. The authors conclude ‘The present study, to date, is one of the first to present empirical evidence supporting the “Greta Thunberg Effect,” and to offer a potential explanation of why a young leader could be a powerful influence on collective action’.

Dr Shireen Kassam, RAC member.

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