The top 10 studies of 2019 supporting plant-based nutrition for health
1. The Eat-Lancet Commission on food, planet, health.
The year started with the publication of the most up to date analysis of what constitutes a healthy diet. Conducted by the Eat-Lancet Commission on Food, Planet, Health, the review brought together 37 experts from 16 countries. They analysed data from several studies on nutrition and health, taking into account country-based differences in accessibility to various foods. The recommended reference diet, termed the ‘Planetary Health Plate’, is one that is composed predominately of whole-plant foods, emphasising fruits, vegetables, whole grains, legumes, nuts and seeds. Animal-derived foods constitute less than 15% of daily calories and there is acceptance that a healthy diet does not need to contain any animal-derived foods at all. Eggs, dairy and poultry are termed ‘optional’. In Europe and America this dietary pattern requires a dramatic reduction in the consumption of unhealthy foods, including at least a 50% reduction in the consumption of red meat. At the same time, a more than 100% increase in consumption of whole plant foods is required. It is estimated that the global adoption of this diet pattern could save more than 11 million lives a year, which at present are lost due to consequences of an unhealthy diet, and will significantly help to mitigate effects of food production on climate change.
2. 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease
The 2019 US guidelines on the primary prevention of cardiovascular disease (CVD) now specifically recommend plant-based diets as a means of preventing CVD. This is because of the enormous amount of evidence from observational and interventional studies demostrating that plant-based diets can reduce CVD risk factors including hypertension, hypercholesterolaemia and type 2 diabetes, reduce the risk of developing CVD itself and arrest and reverse already established CVD.
3. Dietary cholesterol does matter
We know that plant-based diets are low/absent in both saturated fat and dietary cholesterol. Those following a vegan/plant-based diet have the lowest blood cholesterol level of any diet pattern. This study was a large analysis of nearly 30,000 participants in 6 observational studies from the US followed for a median of 17.5 yrs. Each additional 300 mg of dietary cholesterol consumed per day was significantly associated with a 17% higher risk of CVD and 18% higher risk of all-cause mortality. Each additional half an egg consumed per day was significantly associated with a 6% higher risk of CVD and 8% higher risk of all-cause mortality. The analysis was able to show that it is the cholesterol in eggs that’s driving this association after adjusting for other elements in the diet. The effects remained despite adjusting for consumption of other unhealthy foods that are often eaten with eggs (bacon, sausage etc). Authors conclusions; ‘Among US adults, higher consumption of dietary cholesterol or eggs was significantly associated with higher risk of incident CVD and all-cause mortality in a dose-response’
4. Plant-based diets and cardiovascular health
CVD remains the top cause of death globally, yet healthy lifestyle behaviours could prevent the majority of cases. This study analysed data from a large prospective cohort study — ARIC — atherosclerosis risk in communities. 12,168 adults were followed for a median of 25 years. Dietary data were analysed in 3 ways to classify participants based on how much of the diet was derived from whole plant foods. The study found that the more the diet was based around plant foods and the lower the consumption of any animal-derived foods the lower the risk of cardiovascular disease, cardiovascular mortality and all cause mortality. Plant-based diets reduced the risk of cardiovascular disease by 16%, cardiovascular death by 32% and risk of any cause of death by 18–25%. Interestingly the consumption of fish and low fat dairy did not have a benefit for cardiovascular health.
The authors conclusion; ‘our study suggest that progressively increasing the intake of plant foods by reducing the intake of animal foods is associated with benefits on cardiovascular health and mortality risk’.
5. Diet and risk of type 2 diabetes
A meta-analysis from Harvard T.H. Chan School of Public Health found that people with the highest adherence to plant-based diets had a 23% lower risk of type 2 diabetes than those with the lowest consumption of whole plant foods. The association was stronger for people whose diets included the most healthy plant-based foods. The study brings together a large body of epidemiological evidence providing the most comprehensive analysis on diet and type 2 diabetes, including health data from 307,099 participants with 23,544 cases of type 2 diabetes.
Mechanisms that may explain the association between predominantly plant-based diets and reduced risk of type 2 diabetes, according to the researchers, are that healthy plant-based foods improve insulin sensitivity and blood pressure, reduce weight gain, and alleviate systemic inflammation, all of which can contribute to the risk of type 2 diabetes.
6. What is the best source of protein — plant foods or animal-derived foods?
The age old question in an era where protein in the diet has become the supreme macronutrient. This study confirms once again that protein from plant sources have benefits for health when compared to animal sources.
These data are from a prospective cohort study from Japan, which followed more than 70,000 adults for a median of 18 years. The consumption of plant protein was associated with a lower risk of dying from any cause and from CVD. Substituting just 3% plant protein for red and processed meat significantly reduced the risk of dying from all causes, cardiovascular disease and cancer. Substitution of 3% energy from plant protein for red meat protein was associated with 34% lower total mortality, 39% lower cancer-related mortality and 42% lower CVD-related mortality. Substitution for processed meat protein was associated with 46% lower total mortality and 50% lower cancer-related mortality. These data confirm the results of similar studies from the US — including the Nurses’ Health Study and the Health Professionals Follow-up study —and a 2019 study from Finland, but it is good to see the same results in an Asian population.
Why is plant protein better for health? Well it does NOT have any of the negative effects of animal protein, which include; packaging with saturated fat particularly in red and processed meat; the production of TMAO from choline and carnitine implicated in heart disease, renal failure and diabetes; higher levels of acid forming amino acids, which need buffering and have been implicated in the development of renal failure; high levels of the amino acid methionine, which when restricted appears beneficial for cancer prevention; no packaging with fibre; elevation of growth factors such as insulin-like growth factor and oestrogens, both implicated in cancer development; very little association with minerals, vitamins and antioxidants that are abundant in plant protein sources. The data across most studies are consistent — swap out animal protein for plant protein from foods such as beans, pulses, soya, nuts and seeds and you will significantly improve your health and live longer.
7. High protein diets are detrimental for kidney health
2019 has seen increasing support for plant-based diet for prevention and progression of renal failure. So much so that the National Kidney Foundation in the US now actively promote plant-based diets as being beneficial for kidney health. High animal protein intake puts a strain on the kidneys due to increased generation of nitrogenous waste products. Animal foods are high in sulphur-containing amino acids and thus provide a high dietary acid load, which increases the risk of renal failure. Plant-based diets reduces dietary acid load as fruits and vegetables are more alkaline. Plant-based diets prevent the risk factors for renal failure including diabetes, hypertension, cardiovascular disease partly due to high potassium and fibre intakes and of course all the other beneficial phytonutrients.
Plant-based diets are generally lower in protein than standard omnivorous diets with around 10–15% of calories derived from protein. The editorial highlighted above discusses the harms of high protein diets. Their conclusion; ‘it is time to unleash the taboo and make it loud and clear that a high-protein diet is not as safe as claimed, as it may compromise kidney health and result in a more rapid kidney function decline in individuals or populations at high risk of CKD. While more studies are needed to shed greater light, and while we expect that discussion will continue on this and other taboo topics, it is prudent to avoid recommending high-protein intake for weight loss in obese or diabetic patients or those with prior cardiovascular events or a solitary kidney if kidney health cannot be adequately protected’.
The editorial is based on the results of 2 studies published in Nephrology Dialysis Transplantation. The first study analysed dietary and kidney data from the Alpha Omega Cohort, which is a prospective study of 4837 Dutch patients ages 60–80 years with a prior history of myocardial infarction. 2255 patients with blood samples at baseline and after 41 months of follow-up were included. The results showed that patients with a daily total protein intake ≥1.2 g/kg/day had a 2-fold faster annual kidney function decline compared with <0.8 g/kg/day. These data did not find a superiority of plant- versus animal-based proteins, which may be related to the fact that two-thirds of the protein eaten was animal-based, making differential analyses less reliable.
The second study was conducted in a national cohort of 9226 South Koreans conducted between 2001–2014. Once again, the decline in kidney function was greater in those consuming the most protein. The study went on to analyse data from another larger cohort of 40 113 people from the Korean National Health and Nutrition Examination Survey (2008–15) and found that higher dietary protein intake increased the risk of kidney failure.
8. Vegan diets for children
Many still question whether vegan/plant-based diets are optimal for children despite the fact that most major dietetic associations around the world are supportive. This is because there are still very few few scientific studies available on the health of vegan and vegetarian children. Given that the number of vegan parents within the population is increasing, so are the number of children being raised as vegan. This gives us the opportunity to study vegan child health more rigorously. This is exactly what this study from German has done.
The VeChi diet study is a cross-sectional study collecting data on diet, lifestyle, height and weight from vegan, vegetarian and omnivorous children in Germany recruited between 2016–2018. This study reports on the health of 127 vegan children aged 1–3 years. The study found that there were no differences in height and weight of vegan children compared to non-vegan children. There were differences in macronutrient intake with vegan children eating more carbohydrates and fiber and omnivores having greater intake of protein, fat and sugar. However all diet groups obtained plenty of protein, above the recommended requirements.
A small note of caution — there were a few more children in the vegan group that were stunted. But when investigated further these children were either not getting enough calories or exclusively breastfed for longer than recommended. Thus the conclusion of the study ‘our results indicate that a vegetarian and vegan diet in early childhood provides comparable amounts of energy and a macronutrient pattern in accordance with recommendations and can ensure normal growth, as there were no significant differences in proxy-reported anthropometrics compared to omnivorous children of the same age. However, the observed small percentage of vegetarian and vegan children in our sample classified as stunted should emphasize the importance of adequate energy and nutrient intake for children on vegetarian and vegan diets’.
9. A review of low carbohydrate diets
The National Lipid Association has reviewed the entire body of evidence on low-carb diets. The conclusions raise concerns and recommend that patients be counseled on the potential short term gains along side the longer term risks. The following conclusions are made about low carb diets;
a. There may be some short term advantages in weight gain but the initial weight loss is due to water loss and there is a greater loss of lean muscle mass. There is no advantage over other diet patterns.
b. Effects on blood cholesterol and LDL is variable with some having a rise in LDL due to high intakes of saturated fat. Triglycerides levels do fall and HDL levels rise, although the latter is not maintained.
c. No advantage for type 2 diabetes when compared to low fat diets but there is a short term advantage in helping people get off diabetes medication. Short term gains do not translate to a greater benefit at 1 year.
d. Effects on BP are inconsistent and most studies do not show an advantage for those with hypertension.
e. No advantage for lowering CRP, a marker of inflammation, and negative changes in the gut microbiome, including greater generation of TMAO.
f. Low carb diet associated with INCREASED risk of DEATH, adverse side effects and people find it difficult to adhere to in the longer term.
Authors conclusions: ‘patients should be encouraged to eat a diet composed of fruits, vegetables, whole grains, legumes, nuts and seeds due to consistent long term benefits for health. This diet pattern can also be lower carb if desired with the help of a dietitian’.
10. The best diet for human and planetary health
This study demostrated that predominately plant-based diets are best for human and planetary health. Diets based around fruits, vegetables, whole grains and legumes have the lowest impact on the environment whilst promoting human health and reducing the risk of our commonest diseases — cardiovascular disease, overweight/obesity, type 2 diabetes and some cancers. Red and processed meats have the worst impact on human and planetary health. The conflict between human and planetary health comes with the consumption of fish. Fish consumption appears to have benefits for human health but is negatively impacting ocean health. Is fish consumption necessary for all? I would suggest that in parts of the world where whole plant foods are readily available, fish consumption is not necessary. However there may be parts of the world where fish consumption is a staple. In these areas we should be looking for alternate solutions. For the UK a whole food plant-based diet should be the aim for all citizens.
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Dr Shireen Kassam, January 2020