A review of the week’s plant-based nutrition news 9th January 2022

Veganuary is underway and I kick off the year by highlighting several benefits of ditching meat and eating more plants, plus the best diets as ranked by experts for the US News and World Report.

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BEST DIETS 2022: Many of us start a new year by reconsidering lifestyle choices, including diet. The annual review of the best diets from the US News and World Report is now out. No surprises and very similar to the rankings in 2021. The Mediterranean diet was voted best diet overall for the 5th year in a row. Vegan diets as always do less well overall as considered restrictive and difficult to follow (although this is just a perception from a predominantly non-vegan panel!). However, rather contradictory to that the Ornish diet (low-fat whole food plant-based) is joint first for heart health for the 11th year in a row and the vegan diet joint 2nd place for type 2 diabetes. Interesting to see the Atkins diet top for fast weight loss. Don’t be fooled though, a meat heavy low-carb diet is not sustainable and has a number of negative long-term health impacts, including increased risk of heart disease, type 2 diabetes and cancer. Of note, Dr Michael Greger and Dr David Katz on the panel of experts.

In essence, the common themes are that a healthy diet composed of predominantly or exclusively plant foods is best for health. There is nothing special about the Mediterranean diet, only that it focuses on fruit, vegetables, whole grains, beans, nuts and seeds whilst minimising red and processed meats and processed foods in general. This appears to be acceptable to more people than an exclusively plant-based diet. However, many of us know how abundant, varied, easy and tasty a whole food plant-based diet really is.

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DIET PATTERNS AND RISK OF INFLAMMATORY BOWEL DISEASE: Patients intuitively know that diet plays a role in their perception of gut health, yet diet and nutrition interventions for inflammatory bowel disease (IBD) are still not common place. IBD is characterised by gut dysbiosis and a disordered immune response triggered by a combination of genetic and dietary factors. In general, healthy diet patterns centred around whole plant foods, whilst minimising animal-derived and processed foods is associated with a lower risk of developing IBD, both Crohn’s disease (CD) and ulcerative colitis (UC). This is because these foods will promote the health of the gut microbiome, thus supporting the immune system and lowering inflammation, and will maintain the health of the gut lining.

The current study investigates the impact of diet pattern in 125,445 participants of a population-based cohort study from the Netherlands called the Lifelines Cohort study. Participants were followed for up to 14 years. During this time, 224 individuals developed UC and 97 developed CD. Data on dietary intake was collected and analysed. Overall, this population was not eating a great deal of healthy plant foods with a mean of 137g fruit/day (<2 portions), 10g of legumes, 12g nuts and 103g vegetables. Red and processed meat consumption was around 70g/day.

Results showed that a ‘Western-style’ diet pattern characterised by high intake of snacks, prepared meals, non-alcoholic beverages, condiments, and sauces along with low vegetables and fruit consumption was associated with a 16% increased risk of developing CD. A ‘carnivorous’ pattern, including high consumption of red meat, poultry and processed meat, was associated with an 11% increased risk of developing UC. Healthy diet patterns, including those that were most consistent with the dietary guidelines of the Netherlands, were associated with a lower risk of developing CD.

A growing body of evidence now supports a more plant-based diet for prevention of IBD. The most studied diet pattern is the Mediterranean diet, which has been associated with a lower incidence of IBD. In addition, short terms studies have also showed a benefit of the Mediterranean diet for treatment of IBD and its complications. In contrast, a meta-analysis from 2015 demonstrated a positive association between meat consumption and the development of IBD. The most up to date recommendations for patients with IBD are to limit the consumption of red meat, saturated fat, processed foods and food additives, whilst increasing the consumption of fruit and vegetables.

The use of plant-based diets in IBD has been pioneered by Japanese researchers who have been using this in clinical practice for over 15 years, with remarkable results. Their plant-based diet is really a semi-vegetarian diet that includes yogurt and allows for fish once a week to make it more acceptable to patients. Their plant-based diet scoring system considers eight foods to be preventive factors for IBD (vegetables, fruits, pulses, potatoes, rice, miso soup, green tea, and plain yogurt) and eight foods to be harmful (meat, minced or processed meat, cheese/butter/margarine, sweets, soft drinks, alcohol, bread, and fish). They have achieved very good results and durable remissions in both UC and Crohn’s and have also demonstrated higher remission rates in combination with biologic therapies. They have not seen a negative impact with the high fibre content despite the prevailing advice to limit fibre consumption in the acute phase of the disease.

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RED AND PROCESSED MEAT CONSUMPTION AND COLORECTAL CANCER: In 2015, the WHO classified processed red meat as a group 1 carcinogen (definite cancer causing agent) and red meat as a group 2a carcinogen (probable cancer causing agent). This was after assessing data from over 800 scientific publications. The data demonstrated that 50 grams of processed meat eaten daily increases the risk of colorectal cancer (CRC) by about 18% and 100g of red meat eaten daily increased the risk by 17%. This overall means about 1 extra case per 1000 population and for the UK equates to around 8400 cases per year, 20% of the total 42,000 cases when considering both red and processed meat consumption.

This new study assesses the impact of of red and processed meat consumption in a study of black American women. 52, 695 participants were followed for up to 22 years. Total red meat consumption in this population was a median of 35g per day (quite low). Based on analysis of dietary data and incidence of CRC during follow up, the results showed that the consumption of unprocessed red meat increased the risk of all CRC cases by 33% with the impact greatest for those over the age of 50 years. Unprocessed red meat consumption had a greater impact on rectal cancer specifically, increasing the risk by 222%. These results were based on comparing those consuming <2 portions of red meat per week versus 4 or more portions per week. The combination of high red meat intake and low consumption of fruits and vegetables (<5 portions per week) was associated with the greatest increase in risk. In contrast, higher consumption of fruit, vegetables and whole grains afforded some protection even in the context of high red meat consumption.

Interestingly, there was no association found between processed red meat consumption and CRC risk. This may be because processed red meat consumption accounted for less than 30% of red meat eaten and even in the highest tertile of consumption was only 26g per day. In the UK, the split is the other way around with 70% of red meat consumed classified as processed. Also, the commonest type of CRC in black Americans is proximal i.e. higher up in the colon, and prior studies on anatomical site have also failed to show an association between processed meat consumption and proximal CRC but rather more distal cancers.

This study makes an important contribution to the literature as the WHO classification was based mainly on studies conducted in white populations with the data less clear in those from other ethnicities. It also emphasises the important of overall dietary pattern, such that high consumption of fruit, vegetables and whole grains with lower or no consumption of red meat affords the greatest protection against colorectal cancer.

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Full paper

RED MEAT, OBESITY AND NON-ALCOHOLIC FATTY LIVER DISEASE (NAFLD). NAFLD is the accumulation of fat in the liver. When progressive, it can lead to liver fibrosis and cirrhosis. The incidence of NAFLD is rising, with up to 20% of the UK population having some evidence of NAFLD. The key drivers of NAFLD are obesity, dyslipidaemia, insulin resistance and metabolic syndrome. These factors are intimately related to diet and lifestyle. The specific components of diet that are associated with an increased risk of NAFLD include, saturated fat, red and processed meat, refined carbohydrates and fructose (from sugar and high fructose corn syrup). Can you believe that NAFLD was not even recognised as a clinical entity prior to 1980!

This new analysis from the Nurses’ Health Study-2 included 77,795 participants with 3130 cases of NAFLD diagnosed during the more than 20 years follow-up. The results shown that consumption of total red meat, unprocessed red meat, and processed red meat is associated with a dose-dependent increase in the risk of NAFLD. Intakes of total red meat of 2–4, 5–6 servings/week, 1 and 2+ servings/day were associated with 20%, 31%, 41%, and 52% increases in risk of NAFLD respectively when compared to 1 serving/week or less. The corresponding estimates for unprocessed red meat were 32%, 32%, 52% and 50% increase in risk. Processed red meat intakes of 1–3 servings/month, 1, 2–4, and 5+ servings/week were associated with 16%, 24%, 41% and 56% increased risk of NAFLD when compared to <1 serving/month.

Intakes of hamburgers (103% increase in risk per 1 serving/day), hot dogs (227%), bacon (150%) and beef, pork or lamb as sandwich/mixed dish (62%) were all associated with an increased risk of NAFLD. A 49% increase in risk was also observed per 1 serving/day increase in poultry intake. These associations were largely mediated by body mass index, meaning that meat consumption increases the risk of overweight and obesity and thus increases the risk of NAFLD.

Replacing 1 serving/day of total red meat with 1 serving/day of plant-based proteins, nuts or whole grains was associated with a 6%, 6% and 5% reduction in risk, respectively. Interestingly substituting red meat for legumes, dairy or fish was not associated with a lower risk of NAFLD. Of note, legume consumption was pretty low in this cohort with a maximum of around 0.3 servings per day.

The available evidence on dietary management of NAFLD, which also takes into account the importance of weight loss, has been summarised in an excellent review paper.

  1. 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.
  2. Reduce intake of red and processed meats
  3. Reduce/eliminate refined carbohydrates and especially fructose
  4. Increased fibre intake through the consumption of fruits, vegetables, whole grains and legumes
  5. Replace dietary saturated fatty acids with mono-unsaturated and poly-unsaturated fatty acids
  6. 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.

Diets that incorporate these recommendations include plant-based diets such as the DASH, Mediterranean, vegetarian, and vegan diets. These diet patterns are associated with a more healthy weight and lower risk of fat accumulation in the liver. In particular, healthy plant-based diets have been associated with a lower risk of weight gain with ageing.

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DIET AND COGNITIVE FUNCTION: Healthy plant-predominant diet patterns are associated with a lower risk of cognitive decline with ageing. The best studied is the Mediterranean diet and is recommended by the WHO for prevention of dementia. This current study provides us with a mechanism by which healthy diets may be protective against cognitive decline.

The paper reports data from the prospective three-city cohort study in Europe, including 842 participants with a median age of around 75 years followed for 12 years. The researchers investigated the association between diet and byproducts created by the gut microbiota on the incidence of cognitive decline. They measured memory and cognitive scores using validated tools. The results showed that a higher intake of fruit, vegetables and plant-based foods providing polyphenols and other bioactive compounds was associated with the generation of beneficial gut microbiota-derived compounds that were then related to a reduced risk of cognitive decline. Specifically, biomarkers of coffee, cocoa mushroom and red wine consumption had a protective impact. They also found that saccharin derived from the consumption of artificial sweeteners was associated with an increased risk of cognitive decline and the authors suggest that this may be due to dysregulation of energy metabolism and oxidative stress associated with their consumption. In addition, alcohol had a negative effective, suggesting the benefits from consuming red wine are from the polyphenols and not the alcohol and therefore it would be better to obtain these polyphenols directly from grapes and berries.

A prior analysis from the same study cohort reported blood metabolites derived from dietary components that were associated with a reduced risk of cognitive decline. This included metabolites derived from coffee, cocoa, red wine, fish and citrus fruits. Together, these studies add to the growing evidence that supports a varied plant-based diet, rich in polyphenol compounds, for the prevention of cognitive decline and dementia. Its clear that the gut microbiome plays a crucial role in maintaining optimal health and that dietary factors are key in modulating the health of the gut microbiome.

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DIET AND COVID-19: I have written extensively about diet and COVID-19 over the last two years. You can find these summaries on our website and also a talk given on the topic at the Global Vegfest event. What has become apparent is that a plant-based diet can reduce the risk and severity of COVID-19 infection and some of this positive impact is likely mediated through the gut microbiome.

This is the latest study to assess the impact of dietary habits on severity of COVID-19 in the outpatient setting. The study included 236 patients from Australia and analysed the habitual intake of various food items with severity of COVID-19 symptoms. After controlling and adjusting for various confounding factors it was found that higher intakes of the food groups ‘legumes’ and ‘grains, breads and cereals’ were associated with a reduction in severity of symptoms.

Also this week we have the first report from the UK’s nutraceutical randomised study called Phyto-v, the largest study of its kind so far, investigating the impact of probiotics, inulin and polyphenol supplements on severity of COVID-19 symptoms. The results showed a benefit for the intervention group with faster recovery from symptoms associated with COVID-19. Those participants with poor gut health at study entry benefited the most from the intervention.

All in all, we have very compelling data to support a healthy, fibre- and polyphenol rich diet to improve outcomes from COVID-19. Inclusion of some probiotic foods may be of value too.

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