A review of the week’s plant-based nutrition news 20th September 2020
This week I report two randomised nutrition studies in patients with heart disease, a commentary on the Mediterranean diet pattern and once again highlight the impact of diet choice on the environment.
A VEGETARIAN DIET AS TREATMENT OF ISCHAEMIC HEART DISEASE: Great to see the results of this well designed, randomised study of a vegetarian diet in people with ischaemic heart disease. It’s a short, small study of only 31 patients but does confirm what we know already, that diet interventions should be part of routine clinical practice in addition to standard medical therapy.
The study demonstrated that after 4 weeks, a vegetarian diet, which included eggs and dairy, when compared to a meat-based diet resulted in significantly lower levels of total cholesterol, oxidized LDL-cholesterol and BMI. In addition, the vegetarian diet resulted in beneficial changes in the gut microbiome and plasma metabolites, including TMAO. These changes have previously been associated with lower cardiometabolic risk. What was interesting was that the changes in oxidized LDL cholesterol occurred in people with higher prevalence of particular gut bacteria.
For me this study reconfirms that food CAN be medicine when used in the right context and can be a valuable additional intervention when combined with standard medical therapy. Nonetheless, we need to confirm these results in larger and longer studies. It should be noted that lunch and dinners were provided to participants as frozen meals so any successful long term intervention would have to involve education on healthy diets and cooking skills, ideally involving the whole family.
MEDITERRANEAN DIET FOR HEART DISEASE: Another randomised study, this time in 805 patients with coronary heart disease, comparing the impact of a low fat diet to a Mediterranean diet (Med diet) on cardiovascular events. This paper reports the secondary outcomes examinng the impact of the diets on endothelial function, assessed by flow-mediated dilation (FMD) of the brachial artery.
The Med diet had a minimum 35% of calories from fat (22% MUFAs, 6% PUFAs, and <10% SFAs), 15% proteins, and a maximum of 50% carbohydrates. The low-fat, high-complex carbohydrate diet, was in line with recommendation from the National Cholesterol Education Program (NCEP) and the American Heart Association (AHA), with less 30% total fat (12%–14% MUFAs, 6%–8% PUFAs and <10% SFAs), 15% protein, and a minimum of 55% carbohydrates. In both diets, the cholesterol content was adjusted to less than 300 mg/d. The Med diet group were asked to use virgin olive oil daily aiming for 4 or more tablespoons a day.
After one year, the results showed that measures of endothelial function had significantly improved in the Med diet group compared to the low fat group.
Things to note in this study. The low fat group was not really low fat — which is often considered less than 20% of calories from fat. The low fat group were still consuming 32.7% of calories from fat after 1 year. The low fat group were told to limit nut consumption, which we know benefits heart health and endothelial function and is considered part of a healthy plant-based diet. 40% of the low fat group were still consuming refined carbohydrates from commercial bakery products, sweet pastries more than once per week and it is not clear what proportion of the carbohydrates consumed in that group were from complex carbohydrate sources. After 1 year, compared to the Med diet group, the low fat group were eating less fruits, vegetables, legumes, fish, nuts, red wine and olive oil and more bakery goods. Both groups had similar fibre and saturated fat intakes.
For me the take home message is that the Med diet showed better endothelial function but the study has not proven that a Med diet is better than a low fat diet for the reasons mentioned about. Predominantly because the low fat group were not actually eating an optimal or even a low fat diet. However, I do accept that the Med diet represents a healthy diet pattern that is vastly better than the average diet consumed in high incomes countries. This is supported by most national and international dietary guidelines.
IS A PESCO-MEDITERRANEAN DIET BEST FOR HUMAN HEALTH? This paper proposes that a pesco-vegetarian diet might be an optimal diet for human health. This is defined as a diet of ‘vegetables, fruits, nuts, seeds, legumes, whole grains, and extra-virgin olive oil with fish/seafood and fermented dairy products. Beverages of choice are water, coffee, and tea’. There are some good arguments made in support of this diet pattern, which is clearly going to be healthier than the standard Western diet as it is low in saturated fat, red meat and processed meat and foods. We have known for a long time that those eating a traditional Med diet is associated with better health outcomes compared to many other diet patterns and has been voted the healthiest diet by a panel of experts for 3 years in a row.
However, this review suggests the vegan diet pattern is a less healthy option and argues that fish, eggs, dairy and olive oil are important components for human health. No surprise, I have some objections to these statements. I will keep this brief but encourage you to read the whole review.
- I agree that vitamin B12 is deficient from a vegan diet but a daily or weekly supplement is easy enough to take. If supplemented, vegans are at no more risk of anaemia than omnivores. Vitamin D deficiency is not a ‘vegan’ issue per se. Omnivores also need to supplement if there is insufficient exposure to the sun. Fish and eggs are sources of vitamin D. One large egg contains about 41IU of vitamin D — around 10% of your daily requirement — so alone can not provide the necessary amount of vitamin D. A portion of oily fish may provide your daily requirement but eating fish daily is not sustainable and many communities around the world that do not live by water or the sea have little access to fish. Many foods, including Cow’s dairy are fortified with vitamin D, as are plant milks, so the latter can be a preferred option.
- An increased risk of fractures has been reported in vegans, but only when dietary intake of calcium is low. In the EPIC Oxford study, vegans consuming at least 525mg per day of calcium did not have an increased risk of fracture. Although the meta-analysis cited in the review paper does raise concerns about bone health in vegans, the studies included did not take into account the quality of the vegan diet and in the one study that did, there was no detriment to bone health. So it might be concluded that as long as a vegan diet is meeting calcium requirements there is unlikely to be a detriment to bone health. Even though dairy is a source of calcium, its consumption is not relevant for 70% of the World’s population who are lactose intolerant.
- Depressive symptoms have been reported in people who avoid animal foods but studies can not be interpreted as causal and most studies, including the one cited, have a cross-sectional design and cannot exclude reverse causation — which came first the symptoms or the diet choice? The latest systematic review on the subject was sponsored by the beef industry, yet the only randomised study included in the analysis actually showed benefit of meat avoidance for mental health. Similarly the randomised GIECO study of a vegan diet showed improved parameters of mental health and well-being.
- The review cited concern about an increased risk of haemorrhagic stroke in those avoiding meat and dairy. This is based on one paper, from the EPIC-Oxford study, which analysed both vegetarians and vegans together. In contrast, this more recent study from a Taiwanese prospective cohort including >13,000 participants has reported a significant reduction in ischaemic and haemorrhagic stroke in vegetarians. Vegetarians had approx 60% reduced risk of both types of strokes. This was in spite of lower B12 levels and mainly due to lower rates of high BP. It should be noted that this cohort differs from the EPIC-Oxford in that the Taiwanese Buddhists don’t smoke or drink alcohol and eat more soya foods.
- Although fish consumption is better for health than meat, fish can not be considered essential in the human diet. Some studies show that replacing fish with plant sources of protein improves health outcomes. The most recent Cochrane review on increasing omega-3 consumption for cardiovascular health, including from fish, did not find a benefit. The suggested consumption of 3 or more protions of fish a week for the entire global population can not be considered sustainable given the poor health of our oceans and depleted fish stocks.
- The PREDIMED study is cited as one of the main reasons for adopting this Pesco-Mediterrean diet, but the main positive finding in this study was in a composite/combined end point of cardiovascular events, which included myocardial infarction, stroke and death from cardiovascular disease. The main contributor to this significant reduction in events was due to a reduced risk of stroke, rather than myocardial infarction, in the group randomised to eating nuts (not olive oil). However, there was NO reduction in total mortality between the diet groups. In contrast, when the PREDIMED study was analysed using the provegetarian/plant-based diets score, there was significant reduction in the risk of all cause and cardiovascular mortality in those consuming a diet with a high provegetarian score suggesting that it is the whole plant foods in the diet, which contribute most to the improved health outcomes.
- Olive oil can be a healthy addition to the diet, but it is a calorie dense food with around 120kcal per tablespoon. The recommendation of 4 or more tablespoons a day in the proposed diet pattern will not aid weight loss, a concern when two-thirds of the US and UK population are overweight. Most studies of the Mediterranean diet, including the PREDIMED, study do not show significant benefit for weight loss. In addition, extra virgin olive oil can be expensive with money perhaps better spent on fruits and vegetables, which have a higher concentrations of beneficial polyphenols. The polyphenol content of EVOO is 150–400mg/kg, whereas berries can have 200–500mg per 100g.
In conclusion, although the proposed diet pattern will undoubtably be better for health than the standard Western diet, it is not the only healthy diet pattern, and vegetarian and vegan diets are associated with excellent health outcomes too.
MAINSTREAM MEDIA WARNS ABOUT THE DEVASTATING EFFECTS OF HUMAN ACTIVITY ON ALL FORMS OF BIODIVERSITY: David Attenborough’s latest documentary aired this week in the UK was extremely upsetting, yet necessary viewing. It highlighted the devastating impact of human activity on the planet, specifically the loss of biodiversity of animals, insects and plants. To be introduced to the last 2 white Rhino’s left on the planet was heartbreaking. We are accelerating towards the 6th mass extinction event. Our destruction of natural habitats has caused the current COVID-19 pandemic, contributed significantly to climate change and the extreme weather conditions, degraded and polluted our land and oceans and led to the loss and extinction of countless species. For me the documentary did not provide much hope and did not present the solutions clearly enough. These include the move away from an economy that relies of continual growth, consumerism and fossil fuels. Of course, a global shift to a plant-based diet is also essential.
CAN HUMANITY REVERSE THE DECLINE IN BIODIVERSITY? This paper offers some hope. It suggests that we have a choice and if there is the will we can start to reverse the trends in global biodiversity whilst still providing enough food for the growing human population. Seven scenarios are analysed addressing the supply and demand side of food and increased convervation. This includes sustainably increasing crop yields, increased trade of agricultural goods, reduced waste of agricultural goods from field to fork, a shift to a plant-based diet, increased extent and management of protected areas, increased restoration and landscape-level conservation planning. The modelling showed that with all these interventions two thirds of future biodiversity losses are avoided and the biodiversity trends from habitat conversion are reversed by 2050. The question is, will we act?
HEALTHFULNESS AND SUSTAINABILITY OF DIETS IN THE US: The good news is that we don’t need to choose between personal and planetary health, because a plant-based diet can address both concerns. This study used data from the 2007–10 waves of the US National Health and Nutrition Examination Survey (NHANES). It analysed quality of the diet using the Heathly Eating Index. It then estimated, from prior survey data, the proportion of participants that would be willing to change consumption to remove foods such as beef, with high environmental impact, to foods that have a lower impact. Those identified as most likely to change dietary habits based on knowledge of climate impact were women, those with higher incomes and higher levels of education. The greatest impact was found when beef, poutry and pork was replaced by plant sources of protein. This reduced individual food-related green house gas emissions (GHGE) by 50%, improved the quality of the diet by 9% and decreased for cost of the diet by 10.5%. Most of the reduction in GHGE comes from removing beef from the diet. They found that even if only 16% of the US population made these changes it would result in whole population reductions in 1-day dietary GHGE of 1·2% to 6·7%, equivalent to 22–126 million fewer passenger vehicle km.
The study does not take into account the other impacts of reducing meat consumption, such as benefits for biodiversity, land change use, water pollution and so forth, so the overall impact is likely to be higher. In addition, animal sources of food are very resource intensive and a very inefficient way of producing food for humans. It takes 25kg of feed to produce 1kg of beef for example. Even when considering eggs, the least resource intensive source of animal food, it is still possible to produce twice as much nutritionally similar food from plant sources. A recent paper estimated that if all Americans shifted to a plant-based diet we could feed an additional 350 million people. Considering that 1 in 9 people (almost a billion) globally do not have enough food and remain hungry, a shift to a plant-based diet is an even greater necessity.
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