A review of the week’s plant-based nutrition news 13th February 2022
This week I cover studies on diet, lifestyle and dementia, the continued risk of iodine deficiency, the impact of diet on multiple sclerosis and more evidence for transitioning to a plant-based food system to avert climate catastrophe.
CHRONIC CONDITIONS AND DEMENTIA: Dementia is now a rising global problem, impacting quality of life and adding to the rising cost and burden of healthcare. Currently more than 55 million people live with dementia worldwide, and there are nearly 10 million new cases every year. The Lancet commission on dementia brought together leaders in the field to consolidate knowledge and make recommendations for prevention and management of the condition. It has called dementia ‘the greatest global challenge for health and social care in the 21st century’. The most common type of dementia is Alzheimer’s disease (AD), with vascular dementia being the second most common type. AD is being termed by some as ‘type 3 diabetes’ as it shares many of the diet and lifestyle risk factors and pathogenic mechanisms as type 2 diabetes. In their 2017 report, the Lancet Commission reported that 35% of cases could be prevented through modifiable lifestyle risk factors. These risk factors include tobacco smoking, physical inactivity, depression, hypertension, obesity, diabetes, hearing loss and social isolation. The undated report from 2020 adds 3 further risk factors; excessive alcohol consumption, air pollution and traumatic brain injury. With these now 12 risk factors is it predicted that up to 40% of cases of dementia could be prevented or delayed.
The current paper reports findings from the Whitehall II cohort study which included 10, 308 employees (6895 men and 3413 women) of the British civil service based in London at recruitment to the study and aged 35-55 years. The analysis assessed the association between underlying chronic conditions, termed multimorbidity and the risk of dementia after 32 years of follow up of the participants. The chronic conditions considered were coronary heart disease, stroke, heart failure, diabetes, hypertension, cancer, chronic kidney disease, chronic obstructive pulmonary disease, liver disease, depression, other mental health conditions, Parkinson disease and arthritis.
The most frequent chronic conditions among people with dementia were hypertension, followed by coronary heart disease, depression, and diabetes. The presence of two or more chronic conditions was associated with a 2.4-fold increase in the risk of dementia. The younger the onset of the chronic conditions the higher the risk of dementia with the strongest association at age 55 years. Unsurprisingly, people with 2 or more of these chronic conditions also had a higher risk of death during the follow up period, up to 4.8 times the risk of those without chronic conditions. Of note, a cancer diagnosis was not associated with an increased risk of dementia but was the strongest risk factor for death.
The authors conclude ‘These findings highlight the role of prevention and management of chronic diseases over the course of adulthood to mitigate adverse outcomes in old age. Multi-morbidity is already known to affect use of healthcare services, quality of life, and risk of mortality; our study adds dementia to that list’.
This is actually good news as we know we can prevent the vast majority of chronic conditions by adopting a plant-predominant diet and other healthy lifestyle habits.
VEGETARIAN DIET AND DEMENTIA RISK: This is a timely and much needed study. There has always been a concern that diets that exclude fish may increase the risk of dementia given the lower blood levels of long-chain omega-3 fatty acids. The only study we had to date was a preliminary report from the Adventist Health Study suggesting that meat eaters had a significantly higher risk of developing dementia compared to vegetarians.
This paper analysed data from the prospective Tzu Chi Vegetarian Study. It included data from 5710 participants who were aged 50 years or older at the time of recruitment in 2005 and followed till 2014.The participants were all Buddhist volunteers, 3154 who were non-vegetarian and 1737 who were vegetarian. Vegetarians were classified based on not eating meat, fish, or poultry for at least a year prior to recruitment. The vegetarians were less like to consume alcohol and smoke tobacco and had significantly less diabetes, cerebrovascular disease, and substance use disorder compared to the non-vegetarians.
During the average follow up of 9.2 years follow up period there were 121 cases of dementia (37 vegetarians and 84 non-vegetarians) identified and vegetarians has a 33% reduction in the risk of dementia. Subgroup analysis found that vegetarians were specifically protected against dementia under the age of 75 years. However, these results were not statistically significant due to low case numbers, which in part is likely to be due to the fact that researchers only considering cases of dementia that required medical attention.
The reasons for this benefit of a vegetarian diet includes lower risk of co-morbidities and that plant-based diets address the key drivers of dementia; dyslipidaemia, glucose dysregulation, oxidative stress, inflammation and an abnormal gut microbiome.
There are several limitations with these data as discussed in the paper. In addition, the Taiwanese diet differs from the Western vegetarian diet being higher in soya foods, rice, wheat and salt and less consumption of dairy. Overall, these data provide some reassurance that excluding fish and meat from the diet does not negatively impact brain health and may even be of benefit.
IODINE DEFICIENCY WITH PLANT-BASED DIETS: A reminder that the risk of iodine deficiency needs to be addressed when planning a healthy plant-based diet. However, despite the title of the paper, all diet groups studied, omnivores, vegetarians and vegans, had lower than recommended iodine intakes, but vegans had the lowest intake of all diet patterns. This is not surprising given that in the UK the main sources of dietary iodine are cow’s milk and dairy products. Of course dairy is not a natural source of iodine but cow’s receive iodine in their feed and some iodine comes from the sterilising materials used that then contaminate the milk collection. In addition, some iodine is found in eggs as chickens also receive iodine from their feed.
Iodine is a trace element found in oceans and soils close to the sea. The amount in plants is generally low and depends on the level present in the soil in which they are grown. Seafood and seaweed are sources of dietary iodine, but the risk of iodine deficiency is high globally regardless of diet pattern. Iodine deficiency is the commonest cause of preventable brain damage in children and iodine is also required for thyroid hormone production. Given the serious consequences of such a deficiency many countries have iodised their salt. This is not the case for the UK.
The take home message for those on a plant-based diet is to make sure you are getting the required 150mcg per day of iodine. Options include seaweed (although beware of the risks with excessively high levels), fortified plant milks or a supplement. The Vegan Society factsheet provides excellent information.
MEAT HEAVY DIETS, GUT MICROBIOME AND MULTIPLE SCLEROSIS (MS): MS is an autoimmune disease in which the body attacks the insulation around nerves. It’s not clear what triggers the disease but there is an interaction between genetic, environmental and lifestyle factors. Growing evidence suggests that the health of the gut microbiome is a key factor given its importance in maintaining a healthy immune system. Diet is the main determinant of gut health with a fibre and polyphenol-rich diet being essential.
In this study, the interaction between diet, the gut microbiome and the immune system was investigated in 25 people living with MS and 24 people without the disease. Gut microbiome composition and function, blood immune cell populations and cytokine profiles were analysed. These results were correlated with a four day food diary from participants.
A number of differences were found between those with and without MS with adverse changes in the profile of the gut bacteria and immune cells noted. A meat heavy diet was associated with specific changes in the types of gut bacteria present and had a impact on the proportion of certain immune cells. Meat consumption was associated with lower gut levels of Bacteroides thetaiotaomicron— a bacteria involved with digesting carbohydrates from vegetables and producing short chain fatty acids, essential for maintaining immune health. Blood metabolites also differed with methionine being higher, which was consistent with higher meat consumption in the patients studied. Both lower levels of Bacteroides thetaiotaomicron and higher methionine drives T-cell proliferation and differentiation and activates Th17 cells, which are involved in promoting inflammation. The authors suggest ‘meat or methionine restriction might beneficially decrease the number of circulating inflammatory Th17 cells in MS patients’.
We now have quite a bit of data demonstrating that a meat-based, Western-style diet pattern is a risk factor for developing MS. A plant-based diet is key to prevention and management of the condition, likely due to its beneficial effect on the health of the gut microbiome and thus the immune system. Check out our factsheet on preventing and managing MS with a diet and lifestyle approach.
MORE DATA SUPPORTING A PLANT-BASED DIET FOR CLIMATE HEALTH: The need to transition to a plant-based food system for human and planetary healthy is now irrefutable. This study once again confirms the enormous benefit for reducing greenhouse gas (GHG) emissions that would result if globally we phased out animal agriculture.
Based on the modelling used in the study, phasing out animal agriculture over the next 15 years would stabilise GHG levels for 30 years and offset 68% of carbon dioxide emissions during the rest of this century. This would provide 52% of the net emission reductions necessary to limit global warming to 2 degrees Celsius above preindustrial levels, which scientists say is the minimum threshold required to avert a climate catastrophe. While the complete phase out of animal-based agriculture was projected to have the largest impact, the study found that 90% of the emission reductions could be achieved by replacing ruminants such as cattle and sheep.
Animal agriculture is not only an emitter of carbon dioxide but also emits other potent GHGs, methane and nitrous oxide. In addition, it takes up more than 70% of farmland globally, either for grazing or for growing food for the animals. This land could be released back to natural ecosystems and thus act to remove carbon from the atmosphere and lock it away.