Review of the week’s plant-based nutrition news 14th March 2021
This week I cover the increased risk of diabetes from red meat and haem iron, fish consumption and CVD, the benefits of a vegetarian diet for NAFLD, plant protein for building muscle and the impact of the food system on GHG emissions.
HAEM IRON AND TYPE 2 DIABETES: I have previously covered a number of recent publications confirming the superiority of plant protein over animal sources for improving health outcomes. One reason may be the virtual lack of haem iron in plant foods (although legumes do contain very small amounts).
This paper uses data from a prospective community-based cohort study in China and included 2,696 participants aged 40–72 years at baseline and followed for a median of 5.6 years. The development of type 2 diabetes over this time period was correlated with the consumption of haem iron. The results showed that the consumption of haem iron, particularly from red meat, significantly increased the risk of type 2 diabetes in middle age and older adults. When comparing those consuming the most to the least haem iron, there was an almost doubling of risk of type 2 diabetes. There was no association with total iron or non haem iron consumption suggesting that it is specifically haem iron that promotes the development of type 2 diabetes. The current study did not show a negative impact of haem iron consumption for processed red meat, but this is likely due to the overall low level of consumption.
These data are in line with a recent umbrella study of dietary factors and type 2 diabetes that also found red meat consumption (processed and unprocessed red meat) to be associated with a significantly increased risk type 2 diaebtes. Of course one can not truly separate the impact of red meat per se from just haem iron consumption and it’s easier to consider the impact of whole foods rather than individual nutrients. There are many components of red meat that can contribute to insulin resistance, oxidative stress and inflammation and an altered gut microbiome and thus an increased risk of type 2 diabetes. These include the saturated fat content, the generation of TMAO from carnitine, the higher amounts of branched chain amino acids, the higher generation of AGE’s (advanced glucation end products) and of course the lack of anti-oxidants and fibre. Haem iron, is a pro-oxidant and is also implicated in causing inflammation and insulin resistance. Here is an excellent review paper that summarised the hazards of red meat consumption.
In contrast, a plant-based diet high in fruits, vegetables, whole grains and beans has consistently been associated with a lower risk of type 2 diabetes. You can read my summary of the data on plant-based diets and diabetes here.
FISH CONSUMPTION AND RISK OF CARDIOVASCULAR DISEASE (CVD): The role of fish in the diet remains under active discussion. Overall the observational data does suggest a benefit for health, specifically for heart health, the developing brain and for preservation of cognitive function later in life. However, some of this impact is likely to be due to the fact that those eating fish are eating less red and processed meat. Most of the benefit from fish is attributed to the long chain omega-3 fatty acids (DHA/EPA) present in oily fish, rather than the whole fish per se. There are also concerns about the future impact of exposure to environmental toxins such as mercury, dioxins, PCBs and microplastics. Harm may not be overt now but may become apparent with time.
This large study first analysed the impact of fish consupmtion on CVD and mortality in participants of the PURE study (involving 21 nations) who were free from CVD at recruitment. After a median of 9 years follow-up it was found that the consumption of 175g per week (2 servings per week) was not associated with a reduction in CVD or mortality. Interestingly in the PURE study cohort, fish consumption was associated with a rise in LDL-cholesterol and fasting glucose, lowering of TGs and no impact on HDL-cholesterol.
In contrast, analysis of fish consumption in 3 further cohorts of participants from 40 different nations with known CVD or type 2 diabetes showed that 175g of fish per week reduced CVD events by around 13%, CVD mortality by 22%, sudden cardiac death by 27%, and total mortality by 14%. In one cohort the type of fish was also assessed and it was the fatty/oily fish (such as salmon, sardines, tuna, and mackerel) that was associated with benefit whereas other fish types had a neutral effect. Consuming more than 175g/week did not provide additional benefit. Of note, these was no analysis provided on cooking methods or the impact of exposure to environmental pollutants. The results were adjusted for consumption of other dietary variables such as meat, fruit and vegetable consumption and fish consumption was still found to have a benefit for those with known CVD.
Observational data on fish consumption overall show that fish consumption is associated with a lower risk of heart disease, stroke and death. The proposed mechanism for this is that omega-3 fatty acids which are associated with a lower heart rate, lowers BP, better endothelial function, lowers triglyceride levels, and reduced risk of arrhythmias and hence sudden death. There have only been 2 randomised studies of fish consumption for secondary prevention of CVD, The Diet and Reinfarction Trial (DART) and The Diet and Angina Randomized Trial (DART-2), both in men. The DART study included men who had recently recovered from a heart attack who were asked to consume 200–400g of fatty fish a week. The results showed a reduction in death from all causes, which may have been a consequence of the ability of omega-3 fats to reduce the risk of arrhythmia’s and hence suddent cardiac death. In the DART-2 trial, men with stable angina were randomised to increased fish consumption or fish oil tablets. The results of this study showed a neutral impact of fish consumption but increased risk of death in those consuming the fish oil capsules.
More recent studies of fish oil/omega-3 supplementation have shown variable results with some studies showing benefit and others not. Bringing all the studies together, it seems there is a potential benefit of omega-3 supplementation for reducing the risk of heart disease, further heart attacks in those with established disease and sudden death from arrhythmias but limited impact on the risk of stroke. The results vary based on the formulation, the dose of omega-3 supplements and also the background rate of fish consumption. In populations that consume fish already, adding omega-3 supplements do not have any further benefit.
My take home messages are that it is important to be consuming a diet that prevents heart disease in the first place. We already know that a healthy plant-based diet can significantly reduce the risk of developing heart disease by around 25% when compared with a meat-based diet. The current study does not show a benefit of fish consumption for prevention of heart disease. The question remains as to whether supplementing with an algae-based long chain omega-3 would reduce further the already lower risk of heart disease in people consuming a plant-predominant or plant-exclusive diets. In addition, we know that regular consumption of nuts significantly reduces the risk of heart disease and thus an important part of a plant-based diet.
REMOVING MEAT IS HELPFUL FOR FATTY LIVER DISEASE: I find I write often about non-alcoholic fatty liver disease, as it’s an increasingly prevalent condition in Western societies and is undoubtly due to dietary factors. The disease did not even have a name prior to 1980, yet now it may affect up to1 in 5 adults. There are no effective drug treatments and diet and exercise aimed at losing weight is the best treatment approach.
This randomised study examined the impact of a lacto-ovo-vegetarian diet versus a standard omnivorous weight loss diet in patients with NAFLD. 75 participants completed the 3 month intervention and were included in the final analysis. Both diets were designed to have a 500kcal deficit tailored to the energy requirements of each participant.
The results showed a significantly greater improvement in most of the outcome measures in the vegetarian group, which outperformed the omnivorous diet. This included significant reductions in levels of alanine aminotransferase, body weight, waist circumference, BMI, fasting blood sugar, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), triacylglycerol, cholesterol, low-density lipoprotein cholesterol and systolic blood pressure. In addition, ultrasonography showed a greater reduction in the grade of NAFLD in the vegetarian group. There were significant diffferences between the 2 groups in HDL-cholesterol levels, diastolic blood pressure or other liver enzymes.
The avoidance of meat and increasing fruits and vegetable consumption and hence fibre, seems to be beneficial for people with NAFLD. I recently shared a small study of a vegan diet in NAFLD that also showed benefits for weight loss and improvements in liver function.
The available evidence on dietary management of NAFLD, which also takes into account the importance of weight loss, has been recently summarised in an excellent review paper.
- Calorie restriction with a 500–1,000 kcal daily deficit is an extremely effective lifestyle intervention for both the prevention of NAFLD and histological improvement in patients with established disease. The goal of calorie reduction should be to achieve ≥10% overall body weight loss.
- Reduce intake of red and processed meats
- Reduce/eliminate refined carbohydrates and especially fructose
- Increased fibre intake through the consumption of fruits, vegetables, whole grains and legumes
- Replace dietary saturated fatty acids with mono-unsaturated and poly-unsaturated fatty acids
- Coffee consumption is protective against the development of NAFLD and disease progression. Moderate to heavy alcohol consumption should be avoided in the presence of obesity, NAFLD, and other metabolic risk factors. Abstinence is advised for patients with advanced fibrosis.
ANIMAL VS PLANT PROTEIN FOR ATHLETES: This is a question that is often asked. There is no doubt that athletes can thrive on a plant-based diet and animal foods are not necessary for optimal performance. It’s great to see this backed up by more and more scientific papers. This small study investigated the impact of protein source on muscle mass and strength. 19 vegan and 19 omnivorous men undertook 12 weeks of supervised resistance training. Their protein intake was adjusted to obtain 1.6g/kg/day, including from protein supplements, either soya or whey. Various measures of muscle mass and strength, including muscle biopsies, were performed at the beginning and end of the study. The results showed that both groups had equal gains in muscle mass and strength, demonstrating that plant protein is NOT inferior to animal sources of protein.
The results of this study are in keeping with a previous meta-analysis that demonstrated that soya protein was as effective as various sources of animal protein for building muscle mass and strength, but of course without increasing the risk of heart disease and cancer! Small studies have been conducted specifically in vegans, including one that directly examined the heart function by Echocardiography and maximum oxygen consumption of vegan and omnivore amateur runners. Each group had 22 participants and the results suggested better heart function and cardiorespiratory fitness and endurance for those on a vegan diet. Another study in young, physically active women tested endurance and muscle strength in 28 vegans and 28 omnivores and reported better exercise performance in the vegan group with no disadvantage for muscle strength.
So, in addition to numerous benefits for overall health, athletes who adopt a plant-based diet can expect to have no negative impact on athletic performance with a change performance will improve further.
FOOD SYSTEM AND GREENHOUSE GAS (GHG) EMISSIONS: We know that the global food system is a major contributor to climate change. This is because food production generates GHG emissions, results in land use change, pollutes and degrades soil, water and oceans, results in biodiversity loss and more.
A new study from researchers at the UN’s FAO and the European Commission’s Joint Research Centre in Ispra, Italy analyses data from the Emissions Database of Global Atmospheric Research (EDGAR) and land use/land-use change emissions from the FAOSTAT emissions database. The analysis spans from 1990–2015. The EDGAR database breaks down GHG emissions from each stage of the food chain.
The results show that the global food system is becoming more energy intensive over time due to retail, packaging, processing and transport. Two-thirds of the emissions (71%) come from agriculture due to land use and land use change. The rest comes from all other aspects of the food chain; storage, transport, packaging, waste etc. Methane from livestock and rice production accounts for 35% of food system GHG emissions. Fluorinated GHGs from refrigeration are increasing and contribute around 5% of all emissions at present. Packaging contributes 5.4% of emissions which is more than transportation or other supply chain factors. Of note, a separate report finds that emissions from food waste or food that is not consumed contributes around 8–10% of total food-related emissions. The current study finds also finds that food production has increased over the time period as have GHG emissions. A good summary of this study can be found here.
We only have one viable solution for transforming the food system that will address issues of food security and hunger, climate change and the biodiversity crisis. A plant-based food system would reduce the land required for food production by 75%, with removing beef and dairy from the diet having the greatest impact. Here is a great article summarising the benefits for planetary health of adopting a plant-based diet.
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