A review of the week’s plant-based nutrition news 6th June 2021

This week I cover more benefits of eating fruits and vegetables, carbohydrates are not the enemy, the plant-based advantage for gestational diabetes and methane emissions from animal agriculture.

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DIET AND MENTAL HEALTH: It sometimes seems that data on diet and mental health are conflicting. We all agree that removing processed foods from the diet is best for mental health, but some studies, albeit heavily biased, suggest that avoiding meat consumption may adversely affect mental health. However, when you take a general overview of all the data, common themes emerge. It will come as no surprise to my readers that plant-predominant diets such as the Mediterranean diet, are associated with better mental health and well-being and have even been shown to improve symptoms of depression in randomised studies.

The current paper reports the results of a systematic review of 30 studies that assessed the impact of fruit and vegetables consumption on a variety of mental health outcomes in women, including well-being, quality of life, positive and negative affect, self-esteem, anxiety, distress, depressive symptoms, depression, and suicide.. The studies included came from around the globe including the US, South America, Europe, Japan, Hong Kong and Iran.

The overall take home message is that in 25 out of 30 studies, a higher consumption of fruits and vegetables was associated with improved mental health outcomes. The association was independent of age and included pregnant and postpartum women, children and adolescence.

There are numerous potential mechanisms for this finding. The abundance of brain active nutrients in fruits and vegetables including vitamin A, C, folate, potassium, magnesium, polyphenols and flavonoids. The fibre intake will promote a healthy gut microbiome, required for the production of brain active hormones and chemicals. Healthy diet patterns are also associated with a lower risk of chronic physical illnesses and hence better mental well-being. In addition, consuming more fruits and vegetables will crowd out the foods and nutrients that adversely impact mental health such as refined grains and sugar and saturated fat. Overall, a plant-based diet is consistent with an anti-inflammatory diet, important for reducing the risk of mental health disorders.

An umbrella study from 2019 including 60 papers reported benefits for fruit and vegetable consumption on both physical and mental health and well-being with strong associations for the reduction of cardiovascular disease, certain cancers and depression.

All in all, regardless of your diet pattern its best to load up on a wide variety of fruits and vegetables. Do not fall into the trap of worrying about the high carbohydrate content of these foods. These are healthy and essential carbs that are associated with vitality and good health. Regarding a vegan diet and mental health outcomes, there has been one randomised, multi-centre work place intervention conducted by the Physicians Committee for Responsible Medicine for the company GIECO in the United States. 292 participants across 10 corporate sites, who were overweight and/or had a history of type 2 diabetes, were randomised to a low fat vegan diet composed of fruits, vegetables, whole grains and legumes or to continue their usual diet for 18 weeks. The intervention group also had weekly support meetings. The results showed a significant improvement in mental health well-being, work productivity and reductions in depression and anxiety scores in those on the vegan diet.

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EATING FRUIT DOES NOT CAUSE DIABETES: Yet another study dispelling the myth that too much fruit consumption causes type 2 diabetes. It’s so sad that somehow we have started to fear one of the healthiest foods on this planet.

This prospective study reports outcomes for 7674 participants of the Australian Diabetes, Obesity and Lifestyle Study recruited between 1999 and 2000 with a median age of 45 years at baseline. It examined total fruit intake, individual fruit types and fruit juice consumption and associations with risk of type 2 diabetes. Measurements were performed for fasting and 2 hours post prandial glucose, fasting insulin and insulin resistance.

The results showed that the commonest fruits consumed were apples, bananas and citrus fruits. When comparing the lowest quartile of fruit intake (62g per day) with the highest 2 quartiles (230 and 372 g per day), participants in the higher consumption groups had better measures of glucose tolerance and insulin sensitivity and a 36% reduction in the risk of type 2 diabetes at 5 years.

There are so many potential reasons for these finding including the low energy yet high nutrient content of fruit, rich in fibre, vitamins, minerals, and phytochemicals, all of which may play a contributory role. Both insoluble and soluble fibre are reported to improve glycemic control and improve the health of the gut microbiome. Flavonoids are reported to improve insulin sensitivity, potentially by decreasing apoptosis and promoting proliferation of pancreatic β-cells, and reduce muscular inflammation and oxidative stress. Of note, the consumption of fruit juice did not show a benefit for reducing diabetes risk. Of course, the participants that ate the most fruits also ate more vegetables and less red and processed meat and also have more favorable socioeconomic circumstances. The overall quality of the diet is also very important and can not easily be teased apart from the indivudal components.

Of note, the group eating the most fruit really were not eating a huge amount, a median of 4.5 portions/day. These data are consistent with a large number of other studies and meta-analyses demonstrating the beneficial impact of fruit consumption on type 2 diabetes risk.

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PLANT-BASED DIETS IN PREGNANCY: We covered the topic of plant-based diets in pregnancy in our webinar programme this week. Dr Miriam Martinez-Biarge gave an excellent talk on the current data and evidence. Although it would be great to have more studies on vegan pregnancy, the data we do have suggests that a vegan diet, if well planned, can support a healthy pregnancy with some potential advantages, including less weight gain and better cardiometabolic health. There may be small increased risk of having a small baby, mainly in women with a low BMI. With adequate attention to essential nutrients required in pregnancy, outcomes for both mother and baby outcomes are favourable.

One potential advantage of a plant-based or vegan pregnancy is a lower risk of gestational diabetes (GD). This is of no surprise, as GD shares the same risk factors as type 2 diabetes and those with GD have a 1 in 2 chance of developing type 2 diabetes in the next 5–10 years. GD is also associated with adverse outcomes for baby. A study presented in abstract form in 2020 reported that a healthy plant-based diet was associated with a 19% reduction in risk of developing GD.

The paper highlighted is a review of the evidence and discusses the many reasons why a plant-based diet may reduce the risk of GD. It’s well worth a read as all the mechanisms cited are important for reducing chronic illness in general and the reason why plant-based diets are associated with better health outcomes. No surprises that when it comes to the GD, the benefits of a plant-based include it’s anti-inflammatory and anti-oxidant effects, improved health of the gut microbiome, low glycaemic load, reduced exposure to haem iron, lower energy intake and hence body weight, lower intakes of saturated fat and higher intakes of vitamins, minerals, polyphenols and fibre.

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TRADITIONAL DIET PATTERNS AND HEALTH OUTCOMES: Many traditional and indigenous diet patterns are intrinsically healthy, mainly because they are centred around whole plant foods. We have all become familiar with the Blue Zones, regions in the world where people live the longest and healthiest lives. Diets in these Blue Zones are typically 85–95% plant-based, featuring beans as the main protein source and minimising processed foods. The Tsimane tribe in Bolivia first came to my attention with the publication of a report in the Lancet demonstrating that they had the lowest prevalence of coronary atherosclerosis of any studied population despite a high level of inflammation due to chronic infections (mainly parasitic). The population is around 16,000 strong living in a very traditional way that was prevalent prior to the industrial revolution, with farming, hunting, gathering, and fishing in the Amazon basin.

The current paper examines whether the low rate of cardiovascular disease and its risk factors translates into benefits for brain health, assessed by examining brain volume on CT scanning in 746 study participants aged over 60 years. The Tsimane results were compared to brain MRI scans of people in Europe and the US, reflecting a modern, industrialised population. The results showed that the Tsimane people had a significantly smaller reduction in age-related brain volume loss, with around a 70% slower rate of decline than in the compared Western populations. It is thought that these finding will be protective against the development of dementia.

The authors conclude ‘this study suggests that brain atrophy may be slowed substantially by lifestyles associated with very low CVD risk, and that there is ample scope for interventions to improve brain health, even in the presence of chronically high systemic inflammation’.

When you examine the diet and lifestyle of the Tsimane people, you find they consume an estimated 14% of their average caloric intake from protein, 14% fat, and 72% carbohydrate. Meat protein and fat are acquired by hunting. Non-processed carbohydrates are grown in the form of rice, plantain, manioc, and corn via slash-and-burn horticulture, and the Tsimane also gather wild nuts and fruits. Carbohydrates are high in fibre and very low in saturated fat and simple sugars. The diet lacks trans fats, and is a low fat diet, with an average estimated daily consumption of 38 g fat, with 11 g saturated fat, 14 g monounsaturated fat, and 8 g polyunsaturated fat. Most of a typical Tsimane day involves the physical activity of farming, hunting, food preparation, household chores, and parenting.

Overall, another example of how a plant-predominant (although not exclusively plant-based diet), high in carbohydrates and fibre and low in saturated fat can benefit health.

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METHANE FROM ANIMAL FARMING: We spend a lot of time discussing carbon emissions, but other greenhouse gases (GHG), including methane, are important to consider for their impacts on global warming. Methane is a gas even more powerful than carbon dioxide responsible for around 30% of warming, and even though it lasts for less time in the atmosphere, levels are increasing. Without dealing with the GHG emissions from animal farming, we will not be able to keep global warming below 1.5 degrees C. Yet the global demand and production for meat and dairy is ever increasing. Sadly for the animals, industrialised production in CAFO’s (concentrated animal feeding operations) or factory farms is more efficient, uses less land and is thought to therefore produce less GHG emissions.

This new paper finds that in the US, methane emissions are routinely undercounted because emissions from animals are not corroborated by measuring concentrations of the gas in the air, a major omission. The authors reviewed the data from several atmospheric studies and found consistently more methane than that estimated by the Environmental Protection Agency in the US, in the order of 40–90% higher than previous estimates.

Methane is produced from digestion of food by ruminant animals — mainly cow’s and sheep — and also from the stockpiles of manure generated from all farmed animals. It seems that there is some overly optimist accounting occuring when considering the GHG emissions from animal farming. The good news is that because methane lasts for a shorter time of around 10 years in the atmosphere, we have the ability to rapidly reduce levels. The United Nations is clear that we must address methane emissions now. We have at least one readily available solution that all of us, at least in high incomes countries who are contributing the most, can take today. Please stop eating meat and dairy.

Read this article by Dr Laura Freeman and myself on why health professionals should be leading on this dietary change. Just removing red meat from the diet could have an enormous impact on human and planetary health.

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