A review of the week’s plant-based nutrition news 15th January 2023
This week I focus on non-alcoholic fatty liver disease (NAFLD), a condition that is at pandemic proportion, the commonest cause of liver disease globally and the fastest growing indication for liver transplantation. So what can we do about it?
WORLDWIDE PREVALENCE AND INCIDENCE: It is staggering to read these figures. This recent analysis included 72 publications with a sample population of 1,030,160 individuals from 17 countries for the prevalence analysis, and 16 publications with a sample population of 381,765 individuals from five countries for the the incidence analysis. NAFLD was diagnosed on the basis of imaging in the absence of excessive alcohol consumption and viral hepatitis. The worldwide prevalence has increased significantly and is now estimated to be affecting 32% of people, being higher in men than women. The overall incidence was 46·9 cases per 1000 person-years: 70·8 cases per 1000 person-years in men and 29·6 cases per 1000 person-years in women.
A similar analysis in people with overweight or obesity reported a prevalence of NAFLD 70–75%. NAFLD can eventually lead to liver cirrhosis and liver cancer. This alarming rise in rates has mirrored the rise in overweight/obesity and type 2 diabetes. The key drivers of NAFLD are obesity, dyslipidaemia, insulin resistance and metabolic syndrome. It should be noted that the medical community has being working towards changing the name of NAFLD to metabolic (dysfunction) associated fatty liver disease (MAFLD) given its association with metabolic dysfunction and in recognition of the complex and disparate causes and the wide spectrum of disease severity and natural history.
Ultimately the condition is 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).
MEAT CONSUMPTION INCREASES THE RISK OF NAFLD: This new analysis from the UK Biobank included 372,492 participants with a median age of 56.7 years. Dietary risk factors for development of NAFLD were investigated. During the 12 years of follow-up, 3527 case of NAFLD, 1643 case of cirrhosis, and 669 cases of liver cancer cases were diagnosed. Two dietary patterns were investigated. The prudent pattern characterised by high consumption of salad raw vegetables, cooked vegetables, fresh fruit, dried fruit, oily fish, and non-oily fish. The Western pattern was characterised by a high consumption of processed meat, poultry, beef, lamb mutton, and pork
No surprises here. The researchers found that the Western diet pattern increased the risk of NAFLD, cirrhosis and liver cancer by 18%, 21% and 24% respectively. Higher intakes of red meat, processed meat and poultry were associated with a 17–66% increased risk of NAFLD, liver cirrhosis and liver cancer, while intakes of fruit, cereals (including breakfast cereals) and tea were associated with 11–35% reductions in risk of the same outcomes. Cheese consumption resulted in a 22% lower risk of NAFLD. There was also a dose-dependent reduction in risk of all three liver outcomes with increasing consumption of fibre, specifically from bread and cereals. Fish consumption appeared to have a neutral effect.
Overall, these data are consistent with prior studies that have clearly demonstrated a negative impact of meat consumption on liver outcomes, whilst higher consumption of healthy, fibre-rich plant foods is protective. The beneficial association with cheese consumption in this study is interesting to note. The reasons are not clear but may be related to a beneficial impact of cheese on the gut microbiome, or could represent a substitution effect whereby those consumption cheese were eating less meat.
HIGH MEAT INTAKE INCREASES RISK OF NAFLD IN KOREANS TOO: It is useful when findings from nutrition studies are consistent across different ethnicities. This paper reported findings from a Korean cohort study, which included 44,460 participants, aged 40–69 years. During the 4.2 years of follow-up there were 1553 documented cases of NAFLD. The study investigated the impact of different dietary patterns rather than individual foods. This included the prudent dietary pattern, (characterised by high consumption of potatoes, soybean pastes, beans, tofu, soymilk, green and yellow vegetables, light-coloured vegetables, kimchi, mushrooms, fruits, fish, shellfish and seaweed), the flour-based food and meat pattern (characterised by high intake of noodles and dumplings, wheat flour and bread, red meat and its products, white meat and its products, eggs, dairy products and beverages) and the rice-based pattern (high in rice and other grains).
The results showed that the prudent diet pattern was associated with a 22% and 36% lower risk of NAFLD in men and women, respectively. However, the flour-based food and meat pattern was associated with 29% and 55% increased risk in men and women, respectively. There was no association observed with a white rice pattern.
Overall, the data support a diet high in fibre-rich plant-based foods and the authors propose that this is likely to be beneficial due to being rich in dietary fibre, carotenoids and polyphenols, which lower the total energy intake and result in favourable changes to the gut microbiome. Unsaturated fatty acids from plants and fish also benefit lipid levels in the blood and liver.
PLANT-BASED DIETS PROTECT AGAINST NAFLD: The impact of vegetarian diets on the incidence of NAFLD was examined in the Tzu Chi Health Study from Taiwan. The study included 2127 non-vegetarians and 1273 vegetarians who did not smoke or habitually drink alcohol and did not have hepatitis B or hepatitis C infection. Vegetarians had a 21% reduced risk of NAFLD. Replacing a serving of soya with a serving of meat or fish was associated with 12%–13% increased risk, whereas replacing a serving of whole grains with a serving of refined grains, fruits, and fruit juice was associated with 3%–12% increased the risk of NAFLD.
In a study of 18,345 US adults from the 2005–2010 National Health and Nutrition Examination Survey, a high score on the plant-based diet index was associated with a 21% reduction in risk of NAFLD, but unhealthy plant-based diets (made up of processed foods and refined carbohydrates) did not protect against NAFLD and in fact increased the risk.
The study highlighted above is the latest to examine the impact of a healthy plant-based diet on the risk of NAFLD. Researchers analysed data from a nationwide cross-sectional study, including 3900 US adults. The results showed that a healthy plant-based diet was associated with a 36% reduction in risk of NAFLD. Some but not all of the beneficial effects of a plant-based diet relate to a healthier body weight. The authors conclude ‘Our findings suggest that a plant-based diet rich in healthy plant foods might be associated with lower odds of NAFLD, particularly among US non-Hispanic whites’.
Any shift to a more plant-based diet is beneficial with both the Mediterranean and DASH diets proving to beneficial in randomised studies. It is interesting to note that when researchers have tried to improve upon the Mediterranean diet by adding more plant foods, less meat, green tea, walnuts and Mankai (duckweed), the so-called ‘Green Mediterranean diet’, they have found greater benefits for cardiometabolic health, including NAFLD.
COFFEE CONSUMPTION AND NAFLD: It is interesting that coffee consumption is consistently associated with a reduced risk of NAFLD and other liver-related disorders. In this recent meta-analysis, 7 studies including 71,787 participants aged 20–70 years were analysed with regards to the impact of coffee consumption on NAFLD. Regular coffee consumption reduced the risk of NAFLD by 23%. Four cross-sectional studies, including 1338 participants aged of 20–70 years were then analysed and showed that there was a 32% reduction in risk of liver fibrosis in people already diagnosed with NAFLD. Coffee consumption has also previously been shown to reduce the risk of liver cancer. The optimal ‘dose’ of coffee is generally considered around 3 cups per day.
Of course, coffee consumption is not necessary for good health but if you enjoy it then there is the potential bonus of benefit for liver health.
CONCLUSIONS: When writing on this topic, I always share the take home messages from this excellent review paper. The recommendations apply to prevention and treatment of NAFLD,
- 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.
- Reduce intake of red and processed meats
- Reduce/eliminate refined carbohydrates and especially fructose
- Increased fibre intake through the consumption of fruits, vegetables, whole grains and legumes
- Replace dietary saturated fatty acids with mono-unsaturated and poly-unsaturated fatty acids
- 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.