Review of the week’s plant-based nutrition news 9th May 2021

This week I cover the mighty mushroom, the impact of plant-based diets on mortality, intermittent energy restriction and more reasons to ditch meat from the diet.

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BENEFITS OF CONSUMING MUSHROOMS: Mushrooms are one of the top health-promoting foods in any diet pattern. They are a powerhouse of healthy nutrients including phytochemicals (alkaloids, phenolic acids, flavonoids, carotenoids), fibre, polysaccharides (such as beta-glucan), protein, selenium, vitamins (e.g., niacin, thiamin, riboflavin, ascorbic acid, and vitamins B and D), and the antioxidants ergothioneine and glutathione which may play a significant role in the prevention of cancer. I recently covered a large review of studies on the impact of mushroom consumption on cancer prevention, in which daily consumption of 18g per day compared to 0g per day was associated with a 45% reduction in risk of cancer. That’s about 2 small mushrooms a day! No wonder Dr Joel Furhman’s acronym G-BOMBS emphasises the benefits of mushrooms.

This study examined the impact of mushroom consumption on the risk of death; all-cause and cause-specific mortality. The study included 15,546 participants of the Third National Health and Nutrition Examination Survey (NHANES III) in the US, with a median age of 44.3 years at baseline and followed for a median of 19.5 years. The results showed that participants who reported consuming mushrooms had a 16% reduction in risk of death compared to those that did not consume mushrooms at all. There was a dose-reponse, with the more consumed the lower the risk of death. In this study, those consuming the most were eating around 72g per day. There was no specific association with the cause of death. However, consuming 1 serving of mushrooms per day instead of red or processed red meat reduced the risk of death by 35%. Of note, those consuming mushrooms had a better quality diet in general.

The studies on mushroom consumption and health outcomes are pretty consistent with benefits reported for the prevention of a number of chronic diseases. There is no downside to including mushrooms in the diet and should be encouraged as part of a varied plant-based diet.

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PLANT-BASED DIETS AND MORTALITY: The term plant-based diet can at times be confusing as it does not have a precise definition. In the medical literature this includes vegan, vegetarian and sometimes even pesco-vegetarian diets. To more accurately define healthy versus unhealthy plant-based diets, a number of studies have used the plant-based diet index (PDI) to analyse data from food frequency questionnaires and assess the impact on health outcomes.

This study brings together data from a range of prospective cohort studies that use a broad definition of plant-based diet, including PDI, and vegetarian, vegan, semi-, lacto-, lacto-ovo-, and pesco-vegetarian diets and that reported all-cause, cardiovascular disease, site-specific and total cancer mortalities as well as other causes of death in adult participants. The review includes 12 prospective cohort studies with 508,861 participants and 42,697 deaths from publications dated between 1988 to 2020. Study durations ranged from 4.8 to 25 years. Of note, only 1 study included reported outcomes for participants on a vegan diet separately. The others analysed outcomes for vegans with vegetarian participants.

The results showed that a greater adherence to a plant-based diet was associated with a 10% reduction in risk of all-cause mortality. A vegetarian diet pattern was associated with an 8% reduction in cardiovascular disease mortality and a 23% reduction in risk of coronary heart disease mortality. There was no association with plant-based diets and cancer mortality or other causes of death. Of note, it was found that the association with all-cause mortality reduction was mainly from studies conducted in the US and of shorter duration but with larger numbers of participants. However, after controlling for body weight and alcohol consumption these results became insignificant. In addition, controlling for energy intake also reduced the significance of the results.

Overall, the study has tried to answer the million dollar question as to whether a healthy plant-based diet can improve survival and reduce risk of death from a number of chronic diseases. The results show the difficulty in analysing data from studies with heterogenous data sets, using different definitions of a plant-based diet and in which participants are adherent to various degrees to a healthy plant-based diet opposed to one that is high in processed foods and refined carbohydrates. Despite the inherent limitations of such as study, there is a definite signal to a reduction in mortality with a plant-based diet. With a larger number of studies, a vegetarian diet pattern does consistently show benefit for heart health. These finding are likely to be due to the reduced risk of various risk factors in people consuming a plant-based diet. For example, reduction in risk of hypertension, high cholesterol, weight gain, type 2 diabetes and a healthier gut microbiome. The other aspect is that there is certainly no evidence of harm caused by the consumption of a healthy plant-based diet.

The impact on cancer is difficult to be certain about as cancer is not just one disease, so many varying factors make up our personal cancer risk and there just have not been enough studies. One study not included in this review is from the NutriNet-Sante cohort in which those mose adherent to a plant-based diet had a 15% reduction in incidence of cancer over the 5 year follow-up period. In addition, the two largest studies on vegetarian and vegan health, Adventist Health Study 2 and the EPIC-Oxford study do demonstrate a significant reduction in cancer risk in vegetarians and vegans in the order of 10–20%

The study overall adds to the growing amount of data supporting a healthy plant-based or vegan diet as a good choice to make for both human and planetary health. As always, more data and studies would be useful but I am not sure we will ever have the perfect study on vegan or 100% plant-based diets due to the inherent difficulties of conducting such a study.

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CAN REDUCING ENERGY INTAKE BENEFIT HEALTH? There has been a lot of interest in intermittent reduction in calorie intake amongst lifestyle medicine practitioners as a means of augmenting the effects of healthy lifestyle habits. This is in contrast to continous calorie restriction, which is hard to maintain. There are many ways of doing this such as the 5:2 diet, popularised by Dr Michael Mosley, fasting mimicking diet, developed by Dr Valter Longo, or medically supervised water fasting, pioneered by the TrueNorth Health Centre (more continuous than intermittent) and time restricted feeding (eating within a specific time window each day). There are good reasons to believe that energy restriction may be beneficial. This review summarises the data we currently have on the topic of intermittent (opposed to continuous) energy restriction (IER) in humans. There is a lot of detail, which is well worth reading. Below are the headline messages.

IER is associated with a 4–10% loss in body weight over a 4–24 week period but this does not appear to be superior to the effects of continuous calorie restriction. There is currently very little data beyond 6–12 months to know whether the weight loss can be maintained. It is thought, although not consistently proven, that IER may be better at preserving lean muscle mass than continuous calorie restriction and this may be improved by increasing protein intake and adding physical activity to IER.

There is no convincing evidence that IER is better than continous calorie restriction for people with type 2 diabetes and insulin resistance who are trying to reverse these conditions with both forms of fasting showing a benefit in short term studies. Similarly, IER does not seem to have additional benefits for blood lipid reduction compared to continuous calorie restriction. IER does seem beneficial for reducing blood pressure but the impact may be mostly due to body weight reduction. When considering markers of inflammation, IER may be better at reducing CRP levels than continous energy restriction but does not seem to impact other markers such as IL6 and TNF-alpha.

The main concerns are that there is very little longterm data on safety and efficacy. IER diets have been associated with a number of adverse effects including increased hunger feelings, fatigue, irritability, mood disorders, concentration difficulties and uncontrolled hyperphagia on the days of unrestricted feeding, which is frequently manifested as binge eating disorder. There are also concerns that any type of fasting may disrupt the hypothalamus-pituitary-gonadal axis of young women, promoting menstrual abnormalities and potentially interfering with their reproductive ability.

What we still need to figure out is whether IER offers any further benefit above continuous energy restriction and whether there are any benefits beyond just the weight loss achieved. Based on this review, these types of diets are not ready for primetime adoption and should be reserved for specific situations where healthy plant-based diets have failed to achieve the desired goal. After all, a whole food plant-based diet has been shown to be very effective at weight loss with a natural lowering of energy intake as foods are lower in calorie density but higher in nutrients.

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A THROW BACK TO 2017: A fellow Doctor on facebook alerted me to this study that I had not read before. It focusses on the issue of antibiotic resistance and the threat this poses to human health. One easy way to reduce our use of antibiotics is by changing our food system. Depending on the country, anywhere between 40–70% of antibiotics are used in animals, predominantly ‘food’ rather than companion animals. Our continued demand for meat is one of the key drivers of the increasing use of antibiotic medications. This leads to an increased risk of antibiotic-resistant infections in both humans and non-human animals.

The paper provides some solutions. What caught my attention was that if everyone worldwide limited the intake of meat to 40g/day — the equivalent of one standard fast-food burger per person — we could reduce the global use of antibiotics by 66%. Currently in the UK, on average we consume around 200g of meat per day. Reducing our consumption is something we could all do now. There is no need to wait for the other solutions including better regulation and taxation etc. A world without effective antibiotics is an unimaginable disaster. It is estimated that if current trends continue, 10 million people a year will be dying from antibiotics-resistant infections by 2050. This is something that civil society can not allow to happen. We have been warned.

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FOOD CHOICES AND METHANE PRODUCTION: Methane is a greenhouse gas (GHG) that is 84 times more potent at warming the planet compared to carbon. Some suggest that it’s impact is not so important as it is a much shorter lived gas than carbon, breaking down within 10 years. However, for this actually means we can make a more immediate impact on reducing methane levels, which will support the global aim of preventing warming about 1.5 degrees C. Without lowering methane emissions, these targets can not be met. Unfortunately, methane levels continue to rise. Human-related activities are responsible for more than half of these emissions. This includes 40% of human-caused methane emissions from agriculture, mostly ruminant ‘food’ animals and their manure (32%) and also rice paddy fields (8%). The fossil fuel industry is responsible for around 30% and waste dumps a further 20% of human-related emissions. Methane contributes to air pollution and thus has a significant impact on human health and this also causes damage and loss of food crops.

This new report provides hope as it suggests that methane emission could be cut by 45% by 2030 by implementing measures that are readily available. Such steps could avoid 255 000 premature deaths and help prevent more than half a million emergency room visits from asthma every year. Because ground level ozone also harms ecosystems and plants, the reduced methane concentrations could increase global crop yields by 26 million tonnes per year.

The main step we can all take now is transitioning to a healthy plant-based diet or significantly lowering global consumption of meat and dairy. In the UK this would require up to 50% reduction in the consumption of these ‘foods’ and could overall result in a 25% reduction in GHG emissions from the livestock sector. Healthy diets, less reliant on animal foods, are predicted to prevent 11 million premature deaths per year globally. Rice farming systems need to change too and a more varied consumption of whole grains encouraged. Better rice farming solutions are already available and need more widespread adoption, such as System of Rice Intensification, which uses much less water for irrigation thus generating less methane. Reducing food waste and waste in general is also key. We need to reverse our ever increasing levels of consumption in all sectors. This includes avoiding wasting 30% of the food we produce. Plant-based diets automatically reduce food waste and improve efficiency by removing the crops needed to feed our ‘food animals’. A conservative estimate is that it take 12.5kg of plant protein to produce 1kg of protein from meat when considering ruminant animals.

If you need help and support transitioning to a plant-based diet, check out our 21-day Plant-Based Health Challenge, which now has a weekly live Q&A session via zoom.

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