Review of the week’s plant-based nutrition news 18th April 2021
This week I cover studies on heart health, type 2 diabetes, fasting and a new systematic review on vegan diets and cardiovascular disease.
MOST CASES OF CARDIOVASCULAR DISEASE COULD BE PREVENTED: What an incredible conclusion, especially when the solutions are related to healthy lifestyle habits and have no adverse side effects.
This study from the US included more than 40,000 participants. It analyzed the impact of 7 risk factors for cardiovascular disease (CVD): smoking, body mass index, physical activity, diet quality, total cholesterol, blood pressure and fasting glucose. These are the based on the American Heart Associations 7 risk factors for CVD; Lifes Simple 7.
Of note, a healthy diet was defined as more than 4.5 cups of fruits and vegetables per day, 2 portions of fish per week, 3 or more servings of whole grains per day, less than 1500mg sodium/day and <450kcal/week of sugar sweetened beverages. A plant-strong diet but not exclusively plant-based.
The outcome studied was cardiovascular events, classified as non fatal heart attack, stroke, heart failure and CVD death.
The results showed that by addressing all 7 risk factors, 70% of cardiovascular events could be prevented. That is 2 million cardiovascular events and 1.2 million cardiovascular deaths in the US per year. Shockingly, only 7.3% of the participants actually met criteria for a high cardiovascular health score, meaning that they met the Life Simple 7 criteria, whereas 58.5% has low scores. This demonstrates how much work still needs to be done to support citizens to adopt healthy lifestyles to address these key risk factors.
To potentially wipe out 70% of cardiovascular disease is phenomenal. This is empowering information to help us take back control of our health.
Is fish consumption required? I doubt it. I suspect if they had looked at legume or nut consumption instead, similar or better results would have been obtained. Fish consumption is often a reflection of eating less red and processed meat and a healthier diet in general. Prior studies have shown that a healthy plant-based diet can independently reduce the risk of heart disease by up to 25% and cardiovascular disease in general by up to 30%. In addition, healthy plant-based diets can reduce the risk of stroke, type 2 diabetes, renal failure and cancer and may even reduce the risk of dying overall.
Let’s share this information and make lifestyle habits our top strategy for preventing cardiovascular disease.
VEGAN DIET AND CARDIOVASCULAR DISEASE: A rather understated conclusion to this paper on CVD, which is a bit perplexing. However, taking a deep dive, its not clear that any of the studies included in this systematic review actually addressed the question being asked. Those that do, actually point to reduced risk of CVD. However, the studies are not large enough or long enough to make definite conclusions. So the actual conclusion is that more studies are needed.
The systematic review brought together studies that assessed the impact of a vegan diet on cardiovascular disease outcomes or events. A long list of included outcomes can be found in the supplementary data. It does not include biomarkers of cardiovascular health such as blood pressure, cholesterol, body weight, type 2 diabetes.
Only 7 studies met the criteria for inclusion and the authors found a signal for reduced risk of CVD in vegans but the strength of evidence was considered weak. Although in most studies the hazard ratios for cardiovascular outcomes were well below 1, the confidence intervals crossed 1 suggesting that you can not exclude chance as a reason for the findings. However, this is likely a reflection of the overall small numbers of vegans included in the studies and in some, outcomes for vegetarians and vegans are analysed together as in the EPIC-Oxford study.
Despite this, the EPIC-Oxford study did show that there were 10 fewer cases of ischaemic heart disease per 1000 population over 10 years in those consuming a vegetarian diet compared to a non-vegetarian diet. This still offsets the reported increased risk of haemorraghic stroke found in the vegetarian group in this study.
Other studies included don’t really assess the desired outcome. The primary end point of the BROAD study for example was weight loss or change in cholesterol levels on a vegan diet with cardiovascular events being a secondary outcome. This study showed some of the best results for weight loss we have from a randomised study but the follow up was only 12 months and therefore unlikely to be long enough to assess the rate of cardiovascular events. The study only included 65 participants, 33 on a vegan diet, so far too small to reach a firm conclusion. In a similar fashion, the EVADE study only included 100 participants, with half on a vegan diet. The primary end point was change in hsCRP, which the vegan diet was very effective at lowering, but the study was only 8 weeks long so was never going to demonstrate an impact on CVD outcomes.
Although the study by Dr Esselsytn was included, I am not sure why Dr Ornish’s studies were not included. In addition, none of Dr Barnards studies on biomarkers of cardiometabolic health were included.
Without going into every study again, the only conclusion to make is that the studies included are not designed to answer the question being asked. Most are just too small and not long enough. The authors admit there is a lack of data. For the larger EPIC-Oxford and Adventist Health Studies there is definitely a signal that avoiding meat reduces the risk of cardiovascular events. A previous meta-analysis from 2017, including 96 studies, assessed both vegetarian and vegan diet patterns and reported a 25% reduction in ischaemic heart disease in vegetarian and 15% reduction in risk of cancer in vegans.
The issue raised regarding an increased risk of haemorrhagic stroke in the EPIC-Oxford has not been replicated by other study cohorts and in the Tzu Chi vegetarian cohort (not included in this systematic review), there was a reduced risk of stroke and recently a healthy plant-based diet was shown to be associated with a 10% reduction in risk of stroke. You can find my summary on stroke here.
Oddly, the current paper goes on to discuss how vegetarian and vegan diets have been shown to reduce all the risk factors that lead to CVD, including high blood pressure, high cholesterol, overweight, inflammation, type 2 diabetes and generation of TMAO by gut bacteria. A meta-analysis of 40 studies showed a clear benefit of a vegan diet for improving cardiometabolic risk factors. These positive effects are really dependent on the quality of the diet, which the current study does not take into account. If a vegan diet improves all the known risk factors for CVD, this is a pretty major finding.
I do agree with the conclusions ‘our review highlights the need for more studies on the role of vegan diets in cardiovascular health. Further experimental evidence and research in large, ethno-geographically diverse cohorts is warranted to better understand the clinical relevance and public health implications of the vegan diet’. But in the meantime, I think we know enough. A healthy plant-based diet can support optimal health, including cardiovascular health.
RED AND PROCESSED MEAT INCREASES THE RISK OF TYPE 2 DIABETES: This updated analysis from the Nurses’ Health Study and Health Professionals Follow-up Study run from Harvard University examined the impact of swapping out red and processed meat on the risk of type 2 diabetes. This adds more weight to the current evidence on the harm caused by consuming red and processed meat by asking the question ‘instead of what?’.
The study involved 148,853 men and women recruited in 1986 and some in 1991. Data on diet was collected every 4 years. The study investigated changes in red meat intake and simultaneous change in another specified protein source in daily servings over each 4-y period. The protein sources examined were total red meat, including unprocessed and processed red meat, poultry, seafood, low-fat dairy products, high-fat dairy products, eggs, legumes, and nuts. Unprocessed red meat included beef, pork, or lamb as a main dish (e.g., steak and roast), beef, pork, or lamb as a sandwich or a mixed dish (e.g., stew, lasagne, and hamburger). Processed red meat included bacon, hot dogs, sausages, salami, and other processed red meat items. Poultry included chicken and turkey with and without skin and chicken and turkey sandwiches.
The results showed that replacing just one serving of red meat with any other source of protein reduced the risk of type 2 diabetes. When examining the replacement of all types of red meat together with an alternate protein source, animal or plant source, there was a reduction in risk in the order of 10–18%. The reduction was greater when substituting processed red meat for an alternate protein source, in the order of 12–23%. When adjusted for body weight, the risk was attenuated slightly.
Potential mechanisms by which red meat increases the risk of type 2 diabetes include; the haem iron which is pro-oxidant and can cause tissue damage including to the pancreas; saturated fat increases insulin resistance; nitrates and nitrites in processed meat are harmful to pancreatic cells; adverse effects on the gut microbiome and the production of TMAO; cooking meat at high temperatures generates advanced glycation end-products, which causes inflammation and tissue damage. Of course the lack of fibre and phytonutrients in red meat also contribute to the increased risk.
Those that still question the data from observational studies continue to point out the lack of randomised controlled studies on the topic. The editorial by Dr Christopher Gardner that accompanies the current paper explains clearly why we will likely never have a definite randomised study of red meat and incident health outcomes and why this does not matter. We know enough based on observational and mechanistic studies to act accordingly. Red meat causes more harm than good and we should be encouraging healthier choices. There are no randomised studies of tobacco smoking and lung cancer or trans-fat consumption and heart disease, yet the harms caused are self evident.
FASTING FOR METABOLIC SYNDROME: There is much interest in the potential benefits of fasting. However, strong scientific evidence is still lacking, albeit accumulating. Its clear that eating to mirror your circadian rhythm is good for health and having a period of fasting during the day has some additional benefits.
This study examined the impact of a 5 day fast following by the introduction of a healthy, diet pattern — a modified version of the DASH diet — in 35 patients with metabolic syndrome. This group were compared to 35 patients who followed the DASH diet without a period of fasting. The 2 groups also underwent intensive group based behavioural therapy (mind-body program). The fasting group started with two calorie-restricted vegan days (max 1200 kcal/day), followed by 5-days with a daily nutritional energy intake of 300–350 kcal/day, derived from vegetable juices and vegetable broth. After the fast, patients were instructed to follow a modified DASH diet, with additional emphasis on plant-based and Mediterranean diet to optimise refeeding. The non-fasting group was a predominantly plant-based version of the DASH diet. Both groups were on the diet for 12 weeks.
In addition to blood pressure and body weight measurements before and after the intervention, both groups had investigations of the gut microbiome, analysis of immune cells from peripheral blood using immunophenotyping and measurements of blood lipid profile, CRP, IGF-1, renal function and insulin resistance.
There is a lot of complex details, analysis and statistics in the paper. The head line message is that a period of fasting increased the efficacy of the healthy diet and lifestyle intervention. This includes greater improvement in body weight and blood pressure and distinct changes in the microbiome and circulating immune population that have previously been shown to be beneficial.
This is of course a small study and applicability needs to be tested on a larger scale for a longer period of time. However, it does add to the growing evidence that periods of fasting are beneficial to the body and may enhance the benefits of healthy lifestyle interventions.
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