A review of the week’s plant-based nutrition news 17th January 2020
This week is all about the gut microbiome. I also cover the benefits of walnuts and the hazards of alcohol consumption.
GUT MICROBIOME AND SEVERITY OF COVID-19: We have learnt an enormous amount over the last year about the effects of SARS-CoV-2 infection. Initially it was thought of as a respiratory illness, but it soon became clear that the virus has an impact on several organs, including the gut. Not only is the viral receptor ACE2 expressed in the gut, contributing to gastrointestinal symptoms, it has become apparent that the composition of the gut microbiome is associated with severity of infection. We also know that there is communication between microbes in the gut and the lung — the gut-lung axis. In addition, it is the exaggerated and abnormal host immune response to the virus that leads to inflammation and the severe consequences seen with the infection.
This paper from China analysed the composition of the gut microbiome and measured blood markers of inflammation in 100 hospitalised patients with COVID-19 and compared the results to 78 healthy volunteers. Serial stool samples were collected from 27 of the 100 patients up to 30 days after clearance of SARS-CoV-2.
The study found that patients with COVID-19 had significant alterations in the composition of the gut microbiome, including reductions in Faecalibacterium prausnitzii, Eubacterium rectale and several bifidobacterial species that are known to regulate the immune response. These strains of bacteria thrive on dietary fibre and are important in producing short chain fatty acids, which reduce inflammation and regulate the immune system. The study showed that the greater the change in the composition of the gut microbiome the more severe the inflammatory response as determined by the levels of inflammatory markers in the blood. These changes in the microbiota persisted after clearance of the virus. The authors conclude ‘Bolstering of beneficial gut species depleted in COVID-19 could serve as a novel avenue to mitigate severe disease, underscoring importance of managing patients’ gut microbiota during and after COVID-19‘. The authors hypothesize that these persistent changes in the microbiome composition could contribute to the persistence of symptoms after recovery from COVID-19.
Of course there are several limitations to this study. It only includes a small number of patients, many patients received antibiotics as part of their treatment, the changes in the gut microbiome may just be a reflection of the underlying health status of the individual rather than having a causal relationship to the SARS-CoV-2 infection itself. Nonetheless, the gut microbiome is easily modified by healthy lifestyle habits, including a fibre-rich plant-based diet. Previous studies have linked the consumption of fermented vegetables, known to promote the growth of healthy gut bacteria, with a reduced risk of death from COVID-19.
GUT MICROBIOME, DIET AND RISK OF CHRONIC ILLNESS: This new report is from the PREDICT 1 (Personalized Responses to Dietary Composition Trial 1) trial, an international collaboration to study associations between diet, the microbiome, and biomarkers of cardiometabolic health. The researchers collected microbiome sequence data, detailed long-term dietary information, and results of hundreds of cardiometabolic blood markers from just over 1,100 participants in the UK and the US The study examined markers of health such as BMI, weight waist/hip ratio, blood pressure, visceral fat, antibiotic use, fasting and post-prandial lipid and glucose profiles, fatty acids metabolism and markers of inflammation.
The results showed that the composition and diversity of the gut microbiome was strongly associated with specific foods and dietary patterns, which in turn was associated with blood and biometric measures of health. The health of the microbiome and biomarkers had a greater association with dietary factors than with genetics factors, as evidenced by the inclusion of 480 monozygotic and dizygotic twins in the study population.
Participants diets were scored using established healthy eating indices such as the Healthy Food Diversity (HFD) index (incorporating dietary diversity and food quality), the Healthy (hPDI)/Unhealthy Plant-based Dietary Indices (uPDI) (considering quality and quantity of plant-based foods), Healthy Eating Index (HEI) (extent of alignment with US dietary guidelines) and the alternate Mediterranean diet (aMED) score. Adherence to all these healthy eating patterns have been associated with a reduced risk of chronic disease. The results showed that the health of the gut microbiome was strongly associated with the consumption of healthy plant foods with diversity and quality of the diet being most important. The bacterial composition associated with a healthy plant predominant diet were associated with beneficial impacts on markers of cardiometabolic health and inflammation that can predict for a lower risk of developing conditions such as obesity, type 2 diabetes, and cardiovascular disease. The converse was also true in that processed foods, refined carbohydrates and sugar, meat, animal fat and high fat dairy foods were associated with a less healthy gut microbiome composition which was associated with blood markers that predict for an increased risk of chronic disease.
I find it unfortunate that the researchers conclude that microbiome analysis could provide useful information for developing a personalised dietary approach to improve individual health. The truth is that what has been reported, using very detailed and sophisticated analysis, is that the foods associated with the best health are whole plant foods: fruits, vegetables, whole grains, beans, nuts and seeds. The vast majority of the worlds population will thrive on such a diet and drastically reduce their future risk of chronic illness. Yes, its nice to know how the diet works and what effect it has on the gut microbiome, but the message remains the same. For good health, a plant-predominant diet is best and this paper provides us with just one more reason why. In my view, fancy tests are not required for health professionals to give patients this simple, life saving advice.
FIBRE AND THE GUT MICROBIOME: The key question is, what should we be feeding our gut microbiome such that healthy species thrive and unhealthy species are suppressed? This study examined the impact of dietary fibre in controlled feeding experients in human participants who were divided into 3 diet groups; omnivore, vegan and EEN (enteral nutrition diet — a liquid diet with no fibre). There were 3 phases to the study. 5 days of eating the set diet, 3 days of antibiotic and polyethylene glycol (Abx/PEG) to reduce the concentration of bacteria in the gut and then 6 days of recovery when participants were again eating their allocated diets.
This study contains a lot of detailed and complex analysis of the composition of the gut microbiome during the different phases of the study. I won’t pretend to understand the nuances of these data. However, it seems the take home message is straight forward. A lack of dietary fibre causes significant changes in the composition of the gut microbiome. After an acute stress, in this case antibiotics and PEG, fibre is required to restore the health of the gut microbiome. Fibre results in the growth of bacteria that produce short chain fatty acids and metabolise amino acids. These dietary metabolites produced by the gut bacteria are essential for maintaining good health. Removal of fibre in the diet leads to measurable changes in the microbiome within a couple of days.
The good news is that changing your diet to a healthy plant-based one can lead to beneficial changes in the composition of the gut microbiome within days to weeks. In addition, we know from the American Gut Project, that diversity of the diet is also key and consuming at least 30 different plant types a week can have a positive impact on the health of the gut microbiome. It is crazy to think that that just 3 grains, maize (corn), wheat and rice, make up 60% of the world’s food energy intake. Yet, the world has over 50,000 edible plants. Our diet has become so monotonous that globally, 75% of food is derived from 12 plant and 5 animal species. This dietary monotony is in part driven by our ‘modern’ agricultural system which is heavily reliant on monoculture farming. Diversifying the diet can have beneficial impacts on our own health and also the health of the planet. Take a look at this article from WWF and try to add different varieties of plant foods to your diet each week.
ALCOHOL CONSUMPTION AND HEART HEALTH: We have been led to believe that alcohol consumption, particularly wine, in ‘moderate’ quantity can benefit heart health. This seems contradictory to me when alcohol has been classed as a group one carcinogen and contributes to around 5.5% of cancer cases and 5.8% of cancer deaths globally each year. In addition, alcohol-related harm is one of the most common preventable causes of disease worldwide, with 3 million deaths globally attributable to alcohol every year. Alcohol is the leading risk factor for premature mortality and disability among those aged 15 to 49 years, accounting for 10 percent of all deaths in this age group. Alcohol consumption also causes adverse changes to the health of the gut microbiome and increases the permeability of the gut lining. For me, the continued promotion of alcohol for heart health is a hugely successful industry-led marketing tool.
This study examined the association between alcohol consumption and atrial fibrillation (AF), an abnormal heart rhythm that is a major public health concern and increases the risk of heart failure and stroke. The risk of AF increases with age and is predicted to affect 6–12 million people in the US by 2050 and 17.9 million in Europe by 2060. The study included 100,092 participants free of AF, with a median age of 47.8 years at baseline, followed for a median of 14 years. The median alcohol consumption was 3g per day (a standard drink is 12g of alcohol) and there were 5854 cases of atrial fibrillation during the study.
The results showed that all drinks and levels of alcohol consumption were associated with an increased risk of AF. One drink per day increased the risk by 12%. This was despite controlling for conventional cardiac risk factors. There was a clear dose effect with even minimal amounts of alcohol consumption increasing the risk of AF. 3g per day increased the risk by 4%. In contrast, lower doses of alcohol consumption were actually associated with a reduced risk of heart failure independent of the risk of AF. The authors conclude ‘Given recent trials among moderate drinkers showing reduced episodes of AF recurrence after periods of abstinence, and the fact that we found that even low levels of alcohol intake may confer risk, a strategy of reduction of alcohol consumption might have the potential to prevent a substantial number of cases of AF.’
It is not clear why there is a divergent impact of alcohol consumption on heart health with seemingly reduced risk of heart failure. There are clearly better ways to prevent heart failure than turning to alcohol. It’s addictive properties makes it difficult to stick to just ‘moderation’ and balancing risk with any potential gains is impossible as alcohol has a very narrow therapeutic window. Here is an excellent summary of what we know and how to make a personalised decision. However, if you don’t consume alcohol there is certainly no reason for starting now.
INFLAMMATION AND HEART HEALTH: Chronic inflammation is a key driver of ill health. Lifestyle habits, including diet, can either increase or decrease levels of inflammation. All healthy diet patterns, including Mediterranean, DASH, plant-based (vegetarian/vegan) have been associated with lower levels of inflammation. The foods associated with these beneficial effects are predictable as they are foods which have the highest content of anti-inflammatory compounds. You know the answer here.… plant foods are rich in inflammatory compounds such as vitamins, carotenoids, polyphenols, fibre, and omega-3 fatty acids. The most important inflammatory compounds are polyphenols, which are classified into flavonoids and non-flavonoids and are found in a variety of whole plant foods, including tea and coffee. The dietary inflammatory index, which ranks foods based on their ability to cause or inhibit inflammation, can be used to predict the risk of various chronic diseases, including cardiovascular disease and its risk factors, type 2 diabetes and certain cancers.
It’s usually best to concentrate on healthy diet patterns rather than individual foods, but within a healthy diet pattern there are some foods that stand out. Walnuts are one such food. This randomised study included 634 participants from Barcelona, Spain, and Loma Linda, California aged 63–79 years in the WAHA (Walnuts And Healthy Aging) study. Participants were randomised to either the addition of walnuts to the usual diet at 15% of energy (30–60g per day) versus no walnuts for 2 years. Blood inflammatory biomarkers were measured at baseline and at 2 years. The addition of walnuts to the diet did not impact body weight. The results in this paper show that in the walnut group there was a significant reduction in the concentration of 6 of 10 circulating inflammatory biomarkers. These data help provide information on the mechanism for the observed health promoting effects of nut consumption, which are numerous. This study is also the longest and largest nut trial to date!
Inflammatory pathways are a key target for therapeutic drug interventions. In the setting of coronary artery disease, inactivation of the inflammatory cytokine interleukin (IL)-1b by the human monoclonal antibody, canakinumab, and treatment with the anti-inflammatory drug, colchicine have resulted in improved outcomes. Don’t forget though that a vegan diet has also been shown to significantly reduce inflammation to an extent that is not dissimilar to that produced by pharmaceutical interventation. Check out the results of the EVADE study. A vegan diet in this study reduced the level of high-sensitivity CRP, a strong predictor of future adverse cardiovascular events, by 32%.
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