A review of the week’s plant-based nutrition news 18th October 2020

This week I discuss lifestyle interventions for prevention of Alzheimer Disease, dietary risk factors in 2 female cohorts, plant-based diets in kidney failure, the benefit of legume consumption for diabetes and a call to action to reverse biodiversity loss.

PREVENTION OF ALZEIHMER DISEASE (AD): Prevention of AD is key to reducing the global burden of this disease since there are no effective treatment. Addressing established socioeconomic and cardiovascular risk factors appear to be key and once again highlighted by this new paper. The study analysed data from more than 26,000 individuals to determine whether there is a causal relationship between 22 lifestyle risk factors and AD using a Polygenic Risk Score and Mendelian Randomization. Using genetic variants as proxies for modifiable risk factors helps to overcome the limitations of observational studies. The actual methodology is complicated so I won’t dwell on this! The results showed that higher education attainment delayed the onset of AD and increased cortical surface area and thickness of the brain. Higher total and LDL-cholesterol levels were associated with amyloid plaques and lower hippocampal volume. Higher diastolic blood pressure was associated with vascular damage. Out of all the risk factors studied, education attainment, which is a surrogate for cognitive reserve, had the strongest association with AD prevention. Although the study assessed other risk factors, the results suggested that the most effective interventions for preventing AD are focussing on keeping LDL-C and total cholesterol low, blood pressure within the normal range, and making education in all its forms accessible to all.

MORE EVIDENCE TO DITCH RED MEAT: It’s good to see a study reporting health outcomes in women of African decent with results confirming findings of similar studies in Caucasian populations. Shockingly, in 2017, African-American women had a life expectancy of 78.5 y at birth, 2.7 y shorter than that of US white women.

The Black Women’s Health Study (BWHS) is a prospective cohort study of African American women across the USA and started enrolling women in 1995. Health questionaires have been completed at baseline and every 2 years there after. Dietary information was collected at 2 times points. This paper investigated the impact of red meat consumption, both processed and unprocessed, on all-cause and cause-specific mortality in 56,314 women. For red meat consumption, the medium serving sizes were 113 g (4 ounces) for unprocessed red meat, 28 g (2 slices) for bacon, 90 g (2 pieces) for hot dogs, 56 g (2 slices or 2 ounces) for sausage, salami, bologna, and other processed red meats. The analysis compared the lowest quintile of red meat consumption (0.04 servings/day) vs the highest quintile (2.1 servings/day). Women who ate more red meat tended to be younger, have higher BMI, live in neighborhoods of lower socioeconomic status, live in the South or Midwest, smoke more, be less physically active, drink more alcohol, have high blood pressure or diabetes, consume a lower quality diet, and have higher total energy intake. During the 22 years of follow, red meat and processed red meat consumption was associated with a 45% and 40% increase in all-cause mortality, respectively, 62% and 66% increase in cardiovascular disease mortality, 20% and 9% increase in cancer mortality (results for cancer were not statistically significant), and 59% and 53% increase in risk of mortality from other causes. There was a clear dose-response relationship and even modest intakes of unprocessed red meat and processed red meat were associated with increased mortality. Each 1 serving/day increase in red meat consumption was associated with a 7% increased risk of all-cause mortality.

Likely reasons for these findings include the higher consumption of saturated fat, haem iron and salt present in red and processed meat plus the adverse impact on the gut microbiome. In addition, those eating more meat had a worse overall diet quality score suggesting an unhealthy diet pattern. The non-significant findings for cancer mortality are clearly in contrast to results from Causasian cohorts in which red and processed meat consumption does increase cancer mortality. It may just be that the sample size was too small to find a significant effect. It will be interesting to see whether further studies in African’s confirm these findings.

SUGAR AND CARDIVASCULAR DISEASE (CVD): It took a long while for the medical community and policy makers to accept that excessive free sugar consumption is a cause of CVD. This was in part due to a well documented cover up from the sugar industry, who paid scientists to conduct studies that found in favour of sugar consumption and hiding the evidence that clearly showed that sugar consumption was harming health. Half of the sugar in the Western diet is drunk in the form of sugar-sweetened beverages (SSB) rather than eaten. This study examined this impact of SSB consumption on 106, 178 women in the California Teachers Study, a cohort of female teachers and administrators, followed since 1995. Data collected from questionnaires on the consumption of SSB (fruit drinks, caloric soft drinks, and sweetened bottled water or tea) were compared to hospitalization records, specifically examining CVD endpoints including stroke, myocardial infarction, and revascularization (cardiac bypass or angioplasty). The results showed significantly increased risk for CVD (19%), stroke (21%), and revascularization (26%) in women who consumed at least one SSB per day compared to women who consumed none. This was after adjusting for other unhealthy lifestyle factors.

There are several biological mechanisms by which SSBs might impact CVD risk, including an increase in blood glucose and insulin levels leading to a high glycemic load, appetite stimulation, weight gain and contributing to impaired glucose tolerance and insulin resistance. Fructose in sucrose and in the form of high fructose corn syrup alters lipid metabolism and promotes synthesis of triglycerides, thus increasing visceral fat, and also contributes to endothelial dysfunction. Overall, sugar promotes inflammation and oxidative stress, key drivers in the development of chronic illness. It is also possible that SSB consumption may serve as an indicator of a suboptimal diet and unfavorable lifestyle. Individuals who frequently consume SSBs are more likely to follow less healthy diets.

Take home message: Free sugar in all its forms is not good for health and should be minimised in the diet. When it comes to drink, the best choices are water, tea and coffee.

PLANT-BASED DIETS IN RENAL FAILURE: There is now a growing acceptance that a plant-based diet is in fact suitable and probably optimal for those with renal failure. The previous concerns about the high potassium and phosphate and lower protein content of plant foods has been overstated. However, plant-based diets for those on haemodialysis have been less well studied.

This single centre observational study collected dietary data every 3 months for a year on 150 patients receiving haemodialysis. The healthy plant-based diet index was calculated and correlated with serum potassium levels and nutritional status. The results showed that those consuming the most plant foods and least amount of animal foods did not have a higher risk of hyperkalaemia. Although the protein consumption was lower in those most adherent to the healthy plant-based diet index (0.9g/d vs 1.1g/d), patients did not differ in nutritional status and if anything, appeared to have a better overall nutritional status and similar consumption of calories. The authors conclude ‘This observational study challenges our dogmas of routinely recommending patients on dialysis avoid fruits and vegetables and emphasize the importance of performing interventional studies that explore possible benefits and harms of liberalizing the diet of dialysis patients with regards to the consumption of plant foods’.

LEGUME CONSUMPTION BENEFICIAL FOR BLOOD GLUCOSE CONTROL: Legumes are one of the most healthiest foods you can eat, yet we just don’t eat enough. Most dietary guidelines now recommend legumes (which includes beans) as the preferred source of protein in preference to meat for both human and planetary health. In addition to protein, legumes are a source of iron, zinc, potassium, magnesium, niacin, dietary fibre. Nonetheless, because of its high carbohydrate content, there remains confusion over its benefits for blood glucose control. However, legumes are a low glycaemic index food and effective at reducing the postprandial glucose and insulin response compared to that of other carbohydrate-containing foods such as rice and potatoes.

This systematic review included 18 randomised studies; 12 in people without diabetes, 5 with diabetes and 1 with pre-diabetes. The results showed a clear benefit for glucose control, predominantly in patients with type 2 diabetes where regular legume consumption was associated with up to 0.5% reduction in HbA1C. The results for patients with type 1 diabetes, pre diabetes and gestational diabetes were less clear, in part due to the low quality of the studies. Results in people without diabetes were inconsistent. It was noted in studies that considered acceptability of increased legume consumption that a proportion of participants reported abdominal pain, flatulence, bloating, or altered bowel habits. All adverse events were rated as being mild to moderate in severity, with none rated as serious. Given the high dietary fibre content of legumes, and the presence of fermentable carbohydrates, it is not unexpected that the increase in legume consumption caused some discomfort among participants.

It can be concluded that from the avaiable data that legume consumption should be encouraged in patients with type 2 diabetes. Patients should be warned about inital possible gastrointestinal side effects and given tips to reduce abdominal bloating. This can include introducing beans and lentils slowly and starting with lentils can be easier than beans; chew thoroughly and eat slowly; Soaking beans and lentils when cooked from scratch and consider sprouting to make them easier to digest; if using canned beans or lentils thoroughly drain and rinse; cook till soft; use cumin, asafoetida or ginger in cooking; drink plenty of water. Thank you to nutritionist Rohini Bajekal for these useful tips!

PLANT-BASED DIETS AS SOLUTION TO LOSS OF BIODIVERSITY: I hope you have all had a chance to watch David Attenborough's new documentary ‘A life on Our Planet’, available on Netflix. It’s a must watch. It is devastating to see the scale of the loss of biodiversity that has occured during his lifetime. To halt this ecological disaster and restore the planet we need to take several actions, but one important change is a global shift to a plant-based diet. In recognition of this, WWF have produced a new report ‘Bending the Curve: The Restorative Power of Planet-Based Diets’ highlighting the importance of diet choices. The key points taken from the document;

1. Shifting diets can unlock a multitude of environmental and health benefits including combating the climate and biodiversity crises, relieving water stress and eutrophication of lakes and oceans, and saving lives. But these impacts play out differently in countries around theworld and must to be assessed separately for each country.
2. Dietary shifts toward more planet friendly diets is a powerful lever for achieving more ambitious Nationally Determined Contributions (NDCs), a more holistic Post-2020 Global Biodiversity Framework, and a renewed commitment to the Sustainable Development Goals (SDGs).
3. National Dietary Guidelines (NDGs) are important
   tools for changing diets and act as a bridge between global dietary recommendations and local context and relevance. Current NDGs, however, are not ambitious enough to achieve global goals and commitments and should therefore be reviewed and updated to ensure the are in line with global health and environmental targets.
4. Five strategic actions need to be achieved to bend
   the curve on a food system that currently exploits nature to one that restores nature. These actions are 1) reversing biodiversity loss; 2) living within the global carbon budget for food; 3) feeding humanity on existing cropland; 4) achieving negative emissions and; 5) improving water and fertilizer use.
5. A full range of policy levers need to be implemented to leverage dietary changes as a tool for achieving the fivestrategic actions outlined in this report. Countries must commit to closing the evidence gaps that remain regarding specific implications of dietary shifts at the national level and which actions are most effective for their context.

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