Review of the week’s plant-based nutrition news 24th January 2021
This week I cover the impact of plant-based diets on reducing the risk of common chronic diseases, including the new ‘Green-Med’ diet. I look back at a low fat vs keto diet study and there is more on the impact of the global food system on planetary and human health.
ITS NEVER TOO LATE TO REDUCE YOUR RISK OF TYPE 2 DIABETES: We already know that a healthy plant-based diet is best for preventing type 2 diabetes. But what about changes to the diet over time? How does that impact risk?
This paper from the Nurses’ Health Study and Health Professionals Follow-up Study included over 200,000 participants followed for more than 30 years. The analysis examined the impact of adherence to a healthy plant-based diet every 4 years and how changes in adherence impacted subsequent risk of type 2 diabetes. The study used the plant-based diet index to analyse dietary data and the quality of the diet.
The results showed that changes in diet diet quality during follow up had an impact on the future risk of diabetes. Those participants that had better adherence to a plant-based diet over a 4 year period had a significantly reduced risk of type 2 diabetes over the subsequently 4 years. For every 10% improvement in adherence there was a 7–9% subsequent reduction in risk. For those participants whose diet veered away from a healthy plant-based diet there was a 12-23% increased risk of type 2 diabetes in the subsequent 4 years. Participants with the greatest increase in animal food consumption over time had a 10% higher future risk of type 2 diabetes. Some of this increased risk was due to higher body weight
The authors conclude ‘shifting consumption of animal foods away towards more consumption of healthy plant foods over time is followed by a lower diabetes risk’.
We also understand from previous studies the mechanism by which plant-based foods protect against type 2 diabetes. Plant-based diets have anti-inflammatory and anti-oxidant properties, they are higher in fibre and polyphenols, which amongst other things benefit the gut microbiome, the diet is lower in saturated fat and haem iron intake and there is better weight management.
The data supporting plant-based diets for prevention and treatment of type 2 diabetes is so compelling that the American College of Lifestyle Medicine endorse a predominantly whole food plant-based diet as the number one diet intervention in this setting.
THE GREEN-MED DIET: Two papers have recently been published from the DIRECT-PLUS trial, which is investigating the impact of a modified Mediterranean diet on risk factors that predict for chronic illness. The study was conducted in an isolated workplace (Nuclear Research Centre Negev (NRCN), Dimona, Israel) that also has a medical department. Inclusion criteria were age >30 years and presence of abdominal obesity or dyslipidaemia. 294 participants, predominantly men, were randomised into 3 groups. 1) Healthy dietary guidance (HDG) group who were provided with standard healthy eating advice. 2) MED group allocated to a traditional Mediterranean diet emphasising vegetables, with poultry and fish replacing beef and lamb. The diet included 28g/day of walnuts. 3) Green-MED diet group also had 28g of walnuts a day but in addition were advised to avoid red/processed meat consumption. The diet was higher in plants and polyphenols, as the participants were encouraged further to consume the following items: 3–4 cups/day of green tea and 100 g of Wolffia globosa (Mankai strain; a newly developed duckweed grown under highly supervised conditions) frozen cubes, as a green plant-based protein shake, replacing animal protein at dinner. The green tea and Mankai shake were included in the daily calorie count. Both the MED and green MED diets were equally calorie restricted (1500–1800 kcal/day for men and 1200–1400 kcal/ day for women). All 3 groups were provided with guidance on physical activity.
The first paper on cardiometabolic risk showed that at 6 months all 3 diet groups had a similar reduction in calorie intake. The two MED diet groups were consuming less carbohydrates and more fat and protein compared to the control group. The standard MED group were eating more poultry and the Green-MED group much less red and processed meat and more fish. All diet groups were consuming less processed foods, bread, cereals, pasta, potato, sweets and beverages. All 3 groups had a similar increase in physcial activity.
Regarding cardiometabolic risk factors, benefits were seen in all 3 groups but these were greater in the Green-MED diet group with 6.2kg reduction in body weight, 8.6cm reduction in waste circumference, 6.1mg/dl reduction in LDL-cholesterol, 9.3mmHg and 7.15 mmHg reduction in systolic and diastolic BP, respectively. There were also significant reductions in insulin resistance and hsCRP (marker of inflammation). Overall, these improvements were calculated to show a 2-fold fall in the 10-year Framingham Risk Score, which predicts the risk of serious heart disease in the next 10 years.
The author conclusion won’t surprise my regular readers ‘our findings suggest that additional restriction of meat intake with a parallel increase in plant-based, protein-rich foods may further benefit the cardiometabolic state and reduce cardiovascular risk, beyond the known beneficial effects of the traditional Mediterranean diet’
The second paper focussed on the impact of the Green-MED diet on fatty liver disease. Rather alarmingly, 62% of participants had evidence of non-alcoholic fatty liver (NAFLD) disease at baseline. At 18 months follow up, the Green-MED diet group had a 38.9% reduction in liver fat compared to 19.6% reduced in the MED group and 12.1% reduction in the HDG. This benefit remained even after adjusting for the greater weight loss and by the end of 18 months only 31.5% of the Green-MED group had evidence of NAFLD. The extend of liver fat reduction was associated with higher blood folate levels and lower consumption of red and processed meat. Mankai and walnut intake was independently associated with reduction in liver fat. Both the MED diet groups showed significant changes in the composition of the gut microbiome with the extend of liver fat reduction correlated with these changes. The authors conclude ‘a Green-MED diet, enriched with specific polyphenols and decreased red and processed meat consumption, amplifies the beneficial effect of the MED diet on hepatic fat reduction, beyond weight loss’
So do we all need to add green tea and Mankai to our diets? Although these results are impressive, I would suggest there a simpler ways to derive these benefits from a straight forward whole food plant-based diet. All these benefits have already been documented with a plant-predominant or plant-exclusive diet. Green tea for sure is beneficial for health if you enjoy drinking it. Mankai Duckweed is a high protein, aquatic plant that is bred to be high in polyphenols, minerals and is also a plant-based source of vitamin B12. The benefits of the Green-MED diet are proposed to be the higher intake of plants in general, but also polyphenols and of course fibre. Of course, eliminating red and processed meat is a major factor in its success too. A head to head comparison with a straight forward whole food plant-based diet would be great to see.
PLANT-BASED DIET VS ANIMAL-BASED KETO: I thought it was worth writing about this paper again now it has been formally published, in no less than Nature Medicine! The diet wars continue amongst proponents of a plant-based diet and a low-carb, animal-based diet. The ketogenic diet is an extreme version of a low-carb diet, in which the body uses ketones rather than glucose for energy given that carbohydrate intake is severely restricted.
The theory behind the low-carb approach is based on the carbohydrate–insulin model of obesity, whereby intake of high-glycaemic carbohydrates results in elevated postprandial insulin, which is believed to promote body fat accumulation and thereby increase hunger and energy intake. Advocates promote the consumption of non-starchy vegetables and a variety of animal-derived foods, whilst avoiding refined grains, sugar and starchy veg and often limiting fruits consumption. In contrast, the whole food plant-based diet is naturally low in fat and promotes the consumption of all plant foods, including fruits, vegetables, whole grains and legumes, whilst often limiting added oils. Low fat advocates argue that high fat diets lead to overconsumption of calories, have a reduced impact on satiety and promote pleasure signals, thus leading to the passive overconsumption of food/calories.
Some of the seminal studies on the metabolic effects of different macronutrient combinations has been conducted by Dr Kevin Hall, from the National Institute of Health (NIH). Interestingly, Dr Kevin Hall previously headed up the Nutrition Science Initiative (NSI), founded by the low-carb proponent Dr Gary Taubes. However, when Dr Hall’s research showed the complete opposite of the low-carber’s theory on the causes of obesity, he fell out with the NSI and left and the NSI has since all but collapsed.
Dr Hall conducts very rigorous studies known as metabolic ward studies in which participants are admitted to a hospital ward and live there for a set number of days, with all the food provided and undergo an array of blood and metabolic tests. His previous study showed that a ketogenic diet was associated with an increase in markers of inflammation and in LDL-cholesterol and did not improve insulin sensitivity or glucose regulation.
The current study, funded by the NIH, examined a plant-based diet vs an animal-based ketogenic diet and investigated whether ketosis (the generation of ketone bodies) increased fat loss and suppressed appetite. 20 participants, with a median age of 30 years and a median BMI of 28 were admitted to the hospital for 28 days and followed a healthy low fat plant-based diet (75.2% carbohydrate, 10.3% fat) or a low-carb diet (75.8% fat,10.0% carbohydrate) for 2 weeks and then crossed over for 2 weeks on the opposite diet. The participants were offered twice the amount of food they needed on a daily basis and were asked to eat as much as they wanted (ad libitum). The macronutrinent intakes were kept stable in each group with both groups consuming 15% of energy from protein. One volunteer who was enrolled in the study was removed during their first week due to a hypoglycemia episode during the LC diet and these data were excluded from the final analysis.
So what happened to the participants? The low fat plant-based diet had a much higher glycaemic load and resulted in greater postprandial glucose and insulin levels compared with the low-carb diet. However, fasting glucose and insulin decreased from baseline in both groups but this reduction did not significantly differ between the groups. Following a glucose tolerance test, the low-carb group had a relative impairment of glucose tolerance compared to the plant-based diet group. Energy (calorie)intake during the plant-based diet was spontaneously reduced by ~550–700 kcal/d compared to the low-carb diet with subjects losing weight and body fat. This suggests benefits for appetite control. The low-carb group did lose more weight in the first week but this was non-fat mass (water, glycogen and muscle). There were no significant differences reported in feelings of hunger, fullness, satisfaction, or pleasantness of the meals. Triglycerides increased from baseline with the plant-based diet and tended to decrease with the low-carb diet. Although, post-prandial triglyceride levels were higher in the low-carb group. Total and LDL-cholesterol decreased significantly on the plant-based diet as compared to both baseline and the low-carb diet. LDL particle number decreased with the plant-based diet and increased with the low-carb diet. The low fat diet also resulted in significantly lower systolic and diastolic blood pressure
Conclusions: Both models of obesity are disproven by this study. Although the low fat diet with high glycaemic carbohyrates increased postprandial insulin and glucose, participants actually consumed less calories and lost more fat than the low-carb group. This is likely in part due to the satiating ability of fibre. In contrast, the high fat diet did not lead to overconsumption or body fat gain. However, the low-carb group lost less fat, worsened glucose tolerance and had unfavorable changes in blood cholesterol levels. Based on these data the low-fat plant-base diet approach seems more favourable and of course more sustainable.
URGENT CALL TO PREVENT HABITAT LOSS. The global food system is a major driver of both climate change and biodiversity loss. More and more land is being used for agricultural purposes, including grazing animals, growing animal feed and bioenergy crops. 71% of land globally is habitable with half of this land used for agriculture. Almost 80% of this agricultural land is used to raise animals for ‘food’, either for grazing or growing animal feed. Yet, animal-derived food provides only 18% of calories and 37% of protein consumed globally. As the demand for food and particularly animal-derived ‘food’ increases with an expanding and wealthier global population, the predicted increase in land use for growing food is going to have a catastophic effect on the non-human world. Animal and plant habitats are being destroyed leading to an irreversible loss of species and biodiversity
This paper published in Nature Sustainability is a wake up call. It shows shows that the global food system will need to be transformed to prevent habitat loss across the world. If we continue with a ‘business as usual’ approach to food, millions of square kilometres of natural habitats could be lost by 2050. This means that almost 20,000 species of mammals, birds, and amphibians will lose some of their habitat with 1,280 species projected to lose ≥25% of their habitat, making them more likely to become extinct. It shows that what we eat and how it is produced will need to change dramatically to prevent widespread and severe biodiversity losses. In high and middle income countries, a transition to a healthier, plant-based diet whilst also reducing food waste could have significant benefits. The authors discuss that although solutions are currently focussed on conservation practices, there is little discussion on changing what we eat and how it is produced.
The authors conclude ‘Our projections suggest that, under business-as-usual, agricultural expansion will drive widespread and severe biodiversity declines, but that these could be avoided with concerted, proactive efforts to address food consumption and production as ultimate drivers of biodiversity loss’.
The good news is that most of us in high income countries can make the choice to drastically reduce or eliminate the consumption of animal foods. In fact, high income countries are contributing the most to climate change and the ecological crisis, although the global south is suffering the worst of the consequences. There is no necessity for humans to consume meat, fish, eggs and dairy. Shifting to a plant-based diet will go a long way to prevent further loss of biodiversity,
INFECTIOUS DISEASES AND MEAT PRODUCTION: If the ecological crisis and the threat of the six mass extinction is not enough to persuade you to stop eating meat, then may be this paper will. Well worth a read, especially given the current global pandemic. Whether or not SARS-CoV-2 was a result of humans consuming non-human animals, we know that 75% of new and emerging infectious threats come from non-human animals. This is either the direct result of animal farming, especially industrial ‘factory’ farming operations or the encroachment into animal habitats that humans would not normally come into contact with.
This paper outlines all current interactions humans have with non-human animals, all of which increase the risk of an infection jumping from animals to humans. More traditional animal food sources such as bushmeat and backyard farming increase the risks of disease spillover from wild animals. Intensive factory farming creates conditions that can easily generate new infections due to the overcrowding of billions of animals, often in poor health, that are raised indoors every year. Animal farming also contributes indirectly to the spread of infections from wild animals due to deforestation and biodiversity loss associated with the expansion of agricultural land use. These threats may increase due to global warming. Animal farming is also a major driver of antimicrobial resistance, given that most antibiotics used worldwide are for farmed animals often for prophylactic use. COVID-19 has shown that the social and economic costs are enormous. The paper highlights that the impact of infectious threats disproportionally affect the poor.
The paper highlights the importance of reducing meat consumption as a major solution to reducing epidemic and pandemic threats. This has not been a focus for any Government during the current pandemic. The next pandemic infection is likely to be a bird flu, already problematic in poultry farms, including in the UK. However, the paper goes on to suggest that eating insects and cultivating meat could be part of the solution. Here I disagree. We already have the ability to feed 10 billion people with the current level of crop farming. We don’t need new solutions, we need to optimise the solutions we have at our disposal right now.
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