Review of the weeks plant-based nutrition news 6th December 2020
This week the studies reviewed leave no doubt that a plant-based diet is optimal for human and planetary health. Yet despite the evidence, those in power fail to act.
RANDOMISED STUDY OF A LOW-FAT VEGAN DIET: There are very few robust, randomised studies of a low-fat vegan diet. Most of the good studies come from PCRM. Their latest study does not disappoint and is published in a highly reputable journal thus elevating its importance.
In this study, participants aged 25–75 years with a body mass index of 25–40 were recruited through an advertising campaign. The final 244 participants selected were randomised to follow either a low-fat, vegan diet or make no dietary changes for 16 weeks. The intervention diet (approximately 75%of energy from carbohydrates, 15%protein, and 10% fat) consisted of vegetables, grains, legumes, and fruits without animal products or added fats. Vitamin B12 was supplemented (500 μg/d). The intervention group attended weekly classes for detailed instruction and cooking demonstrations and received printed materials and small food samples. No meals were provided. For both groups, alcoholic drinks were limited to 1 per day forwomen and 2 per day for men. All participants were asked to maintain their usual exercise habits and medications unless modified by their doctor. At the beginning and the end of the 16 weeks researchers measured body weight, body fat composition, insulin sensitivity, and the thermic effect of food (postprandial metabolism). In a subset of participants (n = 44), researchers also measured fat in the liver and muscle cells, which contributes to insulin resistance and fatty liver disease, using proton magnetic resonance spectroscopy.
The results showed that the vegan group lowered their body weight by 6.4 kg (about 14 pounds) and the fat inside the liver and muscle cells by 34% and 10%, respectively. They also increased their after-meal metabolism by 18.7%. There were no significant changes in the measured parameters in the control group. The decrease in liver and muscle fat correlated with improvements in insulin resistance.
Things to note, calorie intake based on self-reported assessment, reduced in both groups but more so in the vegan group with a difference of 355kcal/day between groups. Thus the better weight loss achieved was due to a combination of reduced calorie intake and increase postprandial energy expenditure. As expected, the vegan group had a higher carbohydrate and fibre intake and lower fat intake during the 16 weeks compared to the control group. It’s worth noting though that participants were not asked to restrict calorie intake and could eat as much as they liked.
These findings are in line with previous studies that have shown a plant-based/vegan diet naturally lowers calorie intake, increases fibre intake, reduces weight and insulin resistance and lowers fat accumulation in the cells. These are all key mechanims by which chronic illness can be prevented.
The authors conclude ‘A low-fat plant-based diet is an effective tool for reducing body weight and increasing insulin sensitivity and postprandial metabolism’.
CAROTENOIDS AND ALZHEIMER: Plant-based foods are rich in micronutrients that are devoid from animal foods and is one of the main reasons for their powerful impact on disease prevention. This study included 927 elderly participants with a mean age of 81 years from the Rush Memory and Aging Project who were free from Alzheimer Dementia (AD) at baseline and were followed up for a mean of 7 year. There were 237 cases of AD during the follow-up. Along with dietary and clinical evaluation, 508 participants from the cohort who died had Brain AD neuropathology assessed in post mortem brain autopsies.
The study found that higher intakes of carotenoids in the diet was associated with a 48% reduction and the effect was dose-dependent (the more consumed the better the effect). The median highest consumption of carotenoids was 24.8mg/day compared with the lowest consumption of 6.7 mg/d. There was a particularly strong association with the consumption of beta-carotene and lutein/zeaxanthin. The main sources of carotenoids in this study were tomatoes, tomato juice, tomato sauce, carrots, yams/sweet potatoes, squash, kale, and spinach and of lutein-zeaxanthin was vegetables, especially dark-green leafy vegetables. With regards to eating green leafy vegetables, the amount associated with the benefit was 1.3 servings/day. Of note, there was no impact of beta-carotene supplements. Those consuming the most carotenoids also had the least evidence of AD pathology in the post mortem biopsies. These findings were independent of other healthy lifestyle factors.
The theory is that plant-derived nutrients such as carotenoids have anti-oxidant and anti-inflammatory function, therefore addressing the key mechanisms involved in the development of AD. Given that there are no effective medications to prevent or treat AD, a dietary approach seems the best current option. For more information on carotenoids and the amounts found in different food, check out this link.
CAROTENOIDS AND BREAST CANCER: We have known that eating around 10 portions of fruits and vegetables a day significantly lowers the risk of dying from cancer by around 15%. This study examined the impact of carotenoid intake in women at high risk of breast cancer in the Nurses’ Health Study 1 & II. High risk was assessed using a polygenic risk score or by analysing mammographic density of the breast (higher density associated with higher risk). The unique aspect of this study was that plasma carotenoids were measured thus not relying on dietary questionaires.
This was a nested case control study of 1919 cases and 1695 controls. The results showed that higher circulating carotenoids levels were associated with a 20% lower breast cancer risk. The reduction in risk was more pronounced in oestrogen-receptor positive breast cancer cases (27% reduction) and not observed in oestrogen-receptor negative cases. It was also stronger amongst participants with higher genetic breast cancer risk (28.6% reduction) and higher mammographic density (37% reduction).
These data add support to prior studies that show a consistent benefit of carotonoid consumption for prevention of breast cancer. A large meta-analysis of 8 propsective studies showed a consistent reduction, around 10–20%, in breast cancer risk in women with the highest level of circulating the carotenoids. Thus, the authors of the current study conclude ‘our findings support the need to test dietary fruit and vegetable interventions that increase circulating levels of carotenoids as a means of reducing the breast cancer risk, especially for those individuals at high risk’. (Please note that if you carry the BRCA1&2 gene mutations, your risk of cancer is high and standard medical advice should be followed)
ITS NEVER TOO LATE: We know from the results of the randomised Women’s Health Initiative dietary intervention that women with breast cancer who consume more fruits, vegetables and whole grains have an improved survival.
This study examined fruit and vegetable consumption in 8,927 women with breast cancer in the Nurses’ Health Study (NHS 1; 1980–2010) and NHS II (1991–2011) and correlated with the risk of dying from breast cancer and dying from any cause. There were 2,521 deaths, including 1,070 from breast cancer at the time of last follow-up; 2014 in the NHS 1 and 2015 in the NHS II. A greater consumption of total fruit and vegetable and total vegetable consumption was associated with a 18% significantly lower risk of death but not breast cancer–specific death. Fruit consumption alone was not associated with a reduced risk of death. Higher vegetable consumption, particularly green leafy and cruciferous vegetables, was associated with better overall survival among patients with breast cancer. Each 2 servings/week of blueberries was associated with a 25% lower breast cancer–specific and 17% lower all-cause mortality. In contrast, higher fruit juice consumption was associated with a 33% higher breast cancer–specific and 19% higher all-cause mortality.
This study highlights the importance of a healthy overall diet pattern that includes plenty of fruits and vegetables. It also picks out foods that we know are high in anti-oxidants and anti-cancer nutrients, including leafy greens, cruciferous vegetables and berries, that should be a part of our daily diet. Berries of course can be expensive and not always accessible, but the benefit was seen for only 2 servings per week. The study also highlights the importance of whole foods as fruits juice was implicated in a worse prognosis.
RED MEAT AND HEART DISEASE: Over the last year, a number of researchers have published controversial papers that suggest the impact of red meat consumption on health is actually not too bad and we should just continue as we are. This could not be further from the truth and this study adds further evidence of the harm caused by red meat consumption.
The study reported in the BMJ followed 43,272 male health professionals recruited into the Health Professionals Follow-up Study from 1986 and followed for at least 30 years. It examined the association between processed red meat (beef or pork hotdogs, bacon, salami, bologna, or other processed meat sandwiches, in addition to other processed meats such as sausages and kielbasa), unprocessed red meat (hamburger, lean or extra lean, regular hamburgers, beef, pork, or lamb as a main or mixed dish or sandwich and total red meat (both processed and unprocessed red meat) and coronary heart disease. It also investiged the impact of substituting these foods for poutry, fish, eggs, dairy, legumes, soya and nuts. The negative impact of red meat consumption was greater in older men.
The results showed that for every serving of unprocessed red meat per day there was an 11% increase in risk of coronary heart disease and for processed meat a 15% increased risk. If red meat was substituted for a serving of nuts, legumes, whole grains, soya or plant protein in general, there was a 14% reduced risk of heart disease. Swapping red meat for dairy was beneficial and for eggs only beneficial if removing processed red meat. Interestingly substituting red meat for fish and poultry did not have a beneficial impact, which is in contrast to many country-based dietary guidelines. Similar results have previously been reported in women participating in the Nurses’ Health study.
The mechanisms by which red meat causes harm are well know and include increased intake of saturated fat and haem iron (causes inflammation and oxidative stress) and increased total cholesterol and LDL-cholesterol levels associated with meat intake, as well as pro-inflammatory compounds found in meat and the generation of TMAO, a compound associated with the development of atherosclerosis.
CLIMATE HEALTH AND DIET: The 2020 Lancet countdown on health and climate change reports that we are not doing enough; ‘Despite these clear and escalating signs, the global response to climate change has been muted and national efforts continue to fall short of the commitments made in the Paris Agreement’. Regarding our diet choices, it states that unhealthy diets are becoming increasingly prevalent worldwide and excess red meat consumption alone contributed to around 990,000 excess deaths in 2017. Red meat consumption is increasing globally and its production is contributing to the rising concern around climate health. The report states that greenhouse gas emissions (GHG) from livestock increased by 16% between 2000–2007. The food system is responsible for 20–30% of global GHG emissions, most of which originated from meat and dairy farming. Ruminant animal (cows and sheep) farming continues to dominate agriculture’s contribution to climate change and is responsible for 56% of total agricultural emissions and 93% of all livestock emissions globally.
The UN Secretary General stated in a speech this week ‘We are facing a devastating pandemic, new heights of global heating, new lows of ecological degradation and new setbacks in our work towards global goals for more equitable, inclusive and sustainable development…..To put it simply, the state of the planet is broken.”
The data are stark and clear. Let’s demand more and as consumers the most impactful action you can take to holt and hopefully reverse the ecological and climate crisis is to adopt a plant-based diet. Luckily, there is no personal compromise here as we know that a 100% diet can be optimal for human health too.
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