A review of the week’s plant-based nutrition news 27th June 2021

This week I cover an important study on how red meat damages DNA, fatty liver and severity of COVID-19, the impact of healthier lifestyles on inflammatory bowel disease, timing of meals and health outcomes and the diet of early humans.

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RED MEAT CONSUMPTION DAMAGES DNA: This is a really important study. We have known for several years that processed and unprocessed red meat increases the risk of cancer, particularly bowel cancer, but the actual mechanism has been less certain, with many theories proposed.

In this study, DNA was analysed from matched normal and colorectal tumour tissues from 900 patients with colorectal cancer who had participated in one of three prospective cohort studies from the US, the Nurses’ Health Studies and the Health Professionals Follow-Up Study. All participants had previously provided information on their diet, lifestyle, and other factors over the course of several years prior to their colorectal cancer diagnoses.

DNA sequencing data showed different mutation signatures in the different tissues. One particular mutation signature found in the colorectal cancer tissue is associated with alkylation of DNA, indicating a type of DNA damage. This particular alkylating signature was associated with high intakes (more than 150g per day) of processed and red meat prior to the diagnosis of colorectal cancer. However, other dietary factors such as poultry and fish consumption, and lifestyle factors such as body mass index, alcohol, smoking and physical activity was not associated with this alkylating signature. The tumours that displayed the alkylating DNA signature were more likely to have mutations in genes associated with driving the development of colorectal cancer. In addition, this higher levels of alkylating damage was associated with a 47% greater risk of dying from colorectal compared to patients with lower levels of damage.

The lead author was quoted by the American Association for Cancer research to say ‘Our study identified for the first time an alkylating mutational signature in colon cells and linked it to red meat consumption and cancer driver mutations. Our data further support red meat intake as a risk factor for colorectal cancer and also provide opportunities to prevent, detect, and treat this disease.’

The level of red meat consumption considered high in this study really was pretty high at 150g per day, but with all risk factors there is a dose effect and when it comes to red and processed meat, any consumption above 0g is considered to increase the risk of chronic disease. The average level of intake in the UK is around 85g (mostly processed red meat) and in the US 100g per day. It’s interesting to note that many chemotherapy drugs also work by alkylating and thus damaging DNA, with the hope that the impact is greatest on tumour rather than normal tissue. We have so many better food choices to make that act to protect our DNA and prevent cancer. These foods are all the healthy whole plant foods. Red meat is best left off the plate.

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FATTY LIVER DISEASE AND COVID-19: Early on in the pandemic it was clear that people with underlying health conditions were more likely to be hospitalised and ultimately die of COVID-19. Overweight and obesity is a risk factor for a more severe illness with the SARS-CoV-2 virus. This study investigated whether fatty liver disease, often, but not exclusively, associated with obesity, is an independent risk factor for severe COVID-19.

The retrospective study included participants from the UK Biobank study of whom 41,791 underwent MRI (aged 50–83) for assessment of liver fat, liver fibro-inflammatory disease, and liver iron. Positive COVID-19 test was determined from UK testing data, starting in March 2020 and censored in January 2021. 4,458 had a COVID-19 test result available with 1,043 testing positive and 3,415 testing negative. Thirty-two (3.1%) patients who tested positive were hospitalized either 1 week or 1 month after the positive test result. These patients were mostly male and had significantly higher BMI and liver fat compared to other positive patients who did not require hospitalization. The 8 patients were admitted to intensive care had significantly higher liver fat, liver inflammation and BMI compared to all other positive participants who did not require intensive care. Even after a multi-variate analysis with other risk factors, including, age, male gender, non-Caucasian ethnicity, lower socio-economic class and high BMI, fatty liver disease remained a risk factor for more severe disease. Overall, having severe fatty liver disease of greater or equal to 10% was found to be a significant risk factor for testing positive for COVID-19 and hospitalisation. Those participants with fatty liver disease defined by liver fat ≥10% and BMI ≥ 30 kg/m2 were 5.14 times more at risk of being hospitalised with severe disease. This equate to around 11% of the UK population being at risk.

The mechanisms by which fatty liver leads to more severe disease still needs to elucidated and of course the numbers with severe COVID-19 in this study were very small. In the meantime the authors conclude that the results highlight the ‘importance of “de-fatting” the liver to reduce susceptibility’. The good news is that a healthy diet and lifestyle habits are very effective at preventing and reversing fatty liver. I have summarised this topic frequently. Below is the evidence-based approach for prevention and reversal of fatty liver.

  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.

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HEALTHY LIFESTYLES REDUCE THE RISK OF DEATH IN PEOPLE WITH INFLAMMATORY BOWEL DISEASE (IBD): This study highlights how important a healthy lifestyle is even if you already have a chronic illness. The paper reports data from the Nurses’ Health Study and the Health Professionals Follow-up study and assessed the impact of 5 healthy lifestyle factors on risk of death in people with IBD, both Crohn’s disease (CD) and ulcerative colitis (UC). The 5 healthy lifestyle factors were never smoking, normal body mass index, vigorous physical activity, adherence to a Mediterranean diet and light alcohol consumption [0.1–5.0 g/d]. The study included 363 and 465 patients with CD and UC and during follow up 83 and 80 deaths occurred in CD and UC respectively.

The results showed that the main causes of death were cardiovascular disease and cancer. There was an inverse relationship between healthy lifestyle factors and risk of death. Compared to no healthy factors, those with 3–5 healthy lifestyle factors had a 71% reduced risk of death during the follow up. This positive impact of healthy lifestyle factors was not related to severity of the IBD because the relationship held true when taking into account use of immunosuppressive treatment or need for surgery as markers of disease severity.

A healthy Mediterranean diet, which emphasises whole plant-based foods and fish, whilst limiting red and processed red meat and processed foods, reduced the risk of dying by about one third. Maintaining a healthy body mass index, exercising regularly, and light alcohol use of up to 5g per day, were also beneficial. Not smoking improved survival by a factor of four.

Although people with IBD don’t often die of the disease itself, they are at increased risk of dying from cardiovascular disease and cancer when compared with the general population. At a very basic level, these diseases all share in common increased levels of inflammation. Healthy diet and lifestyles are very effective at reducing inflammation and addressing other mechanisms of chronic illness including oxidative stress, unhealthy gut microbiome, insulin resistance, unhealthy body weight, dyslipidaemia, endothelium dysfunction. altered gene expression and shortened telomeres. Anyone of these mechanisms could be at play here. The topic of IBD and cardiovascular disease has been highlighted recently by the American College of Cardiology with this excellent review article. Risk factor modification through adopting healthy lifestyles is their first and foremost recommendation.

Of course, there healthy habits can be difficult for people with IBD but that should not mean we don’t do our best to support patients adopt the healthiest lifestyle possible. It is never too late to make a positive impact on health outcomes. The authors conclude ‘Assessment of healthy lifestyle behaviors should be routinely performed in IBD patients and adherence to such behaviors should be encouraged to improve longevity and promote healthy aging’.

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IMPACT OF TYPE AND TIMING OF FOOD ON RISK OF DEATH: This is a interesting hypothesis-generating analysis. It examines the impact of dietary pattern and timing of consumption on risk of death from all causes, cardiovascular disease and cancer. Prior studies have suggested that consuming more calories earlier in the day and less as the day progresses to match our circadian rhythm is associated with better health outcomes.

The study used data from 21,503 participants in the National Health and Nutrition Examination Survey from the US between 2003 to 2014. Dietary data were collected and food patterns were grouped into the following: Western breakfast (high in refined grains, legumes, added sugar, solid fats, cheese and red meat), starchy breakfast (high in white potato, other starchy foods, milk and eggs), fruit breakfast (high in fruits, whole grains, yogurt and nuts), Western lunch (refined grains, solid fats, cheese, added sugar, cured meats), vegetable lunch (total vegetable, red and orange vegetable, tomato and dark vegetable), fruit lunch (fruit and yogurt), Western dinner (refined grain, cheese, solid fats, added sugars, and eggs), vegetable dinner (total vegetable, red and orange vegetable, tomato, and dark vegetables), and fruit dinner (fruits and yogurt). For the snacks, grain snack (refined grain, whole grain, added sugars, cheese, and eggs), starchy snack (white potato and other starchy food), fruit snack, and dairy snack (dairy products, milk, and cheese) were identified as main snack patterns after main meals.

There were not too many surprises with the results. For main meals, the study found that meal patterns of fruit lunch and vegetable dinner were associated with decreased risks of cancer, CVD, and all-cause mortality , whereas Western lunch was associated with elevated risks of CVD and all-cause mortality. For snack patterns, the study found that snack patterns of fruit after breakfast and dairy products after dinner were associated with decreased mortality risks of cancer, CVD, and all-cause; whereas the starchy snack pattern (mainly a reflection of white potato consumption) after main meals was associated with elevated risks of CVD and all-cause mortality. However, the impact of meal timing was greatest in those with the lowest quality diet.

Interestingly, vegetables at dinner was significantly associated with lower risks of cancer, CVD, and all-cause mortalities, whereas vegetables consumed at lunch did not have these beneficial effects. The authors hypothesise that this may be due to the circadian pattern of metabolism and gut microbiota. For example, abundance of bacteria that use dietary fibre from vegetables to generate short-chain fatty acids is frequently highest at night, and it gradually decreases in the daytime. It may also be due to the fact the vegetable-based meals are lower in calories which is beneficial for meals later in the day. The authors hypothesise that the association of dairy consumption after dinner and reduced mortality could be due to better sleep quality because of the high levels of high levels of tryptophan, which is the precursor of serotonin and melatonin.

Overall, the authors conclude ‘In conclusion, higher intake of fruit at lunch, and higher intake of vegetables and dairy products in the evening were associated with lower mortality risks of CVD, cancer, and all-cause; whereas higher intake of refined grain, cheese, added sugars, and cured meat at lunch, and higher intake of potato and starchy foods after main meals were associated with greater CVD and all-cause mortalities’.

These are interesting findings but I am not sure it is going to change the way I eat. The data has found a number of associations in a population that has one of the worst diet qualities globally and where more than 60% of food consumed is ultra-processed. Concentrating on diet quality first and foremost is more important. Then eating in tune with your circadian rhythm can be addressed with avoidance of eating large meals late at night.

Of course, those of you who follow me know I am not suddenly going to start recommending dairy products as an evening snack. When comparing dairy consumption in the evening to a more typical American post dinner snack of cakes or ice-cream for example then dairy will definitely appear better. If you want to boost your tryptophan levels you can easily do so through consuming plant foods such as pineapple, tofu, nuts and seeds. Foods high in melatonin include cherries, goji berries, pistachios and almonds.

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TURNS OUR WE HAVE BEEN EATING CARBS WELL BEFORE DOMESTICATION OF CROPS: This is a really interesting article dispelling some myths about our ancestral diet prior to domestication of crops. Rather than being hunters and reliant on meat, there is evidence from more than 10,000 years ago that our ancestors were cooking porridge and stews made from grain. By examining residues on ancient tools, such as grinding tools, and dental plaque, it has become apparent that even going back as far as 100,000 years ago people were consuming starchy vegetables and cereal grains, with evidence even for the preparation of bread. It now seems clear that plant-strong diets have been the norm for most of human history and ‘that early humans were cooking and eating carbs almost as soon as they could light fires’. This puts into question the Paleo way of eating which excludes grains, legumes and starchy vegetables, some of the healthiest foods humans can eat.

I highly recommend this talk by Dr Christina Warinner, PhD, from the University of Oklahoma.


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