A review of the week’s plant-based nutrition news 12th June 2022
This week I review studies on low-carb diets and diabetes, phytochemicals and osteoarthritis, benefits of ginger and a guidance from the UK Government supporting health professionals to advocate for climate friendly policies.
LOW-CARB DIETS FOR TYPE 2 DIABETES: I recently highlighted the expert consensus statement from the American College of Lifestyle Medicine, endorsed by a number of American healthcare societies, recommending a plant-based or plant-predominant diet for remission induction in type 2 diabetes. The statement provided a clear warning against low-carbohydrate diets, especially if carbohydrates are replaced with animal sources of protein and fat, given the increased risk of cardiovascular disease, which remains the main cause of death in people living with diabetes. However, the document did acknowledge the short term benefits of lowering carbohdyrate consumption in people with type 2 diabetes. It’s therefore useful to have this updated meta-analysis of randomised studies of carbohydrate restriction.
The novel aspect of this study is that it uses a new statistical method for meta-analysis; dose–response meta-analysis of differences. This uses dose–response models to estimate differences within each study and between studies thus providing an estimate of the impact of a stepped reduction in carbohydrate intake from 55–65% of energy to 10%.
The results show a clear dose-related decrease in haemoglobin A1c (HBA1c), fasting blood glucose, triglycerides, systolic blood pressure and body weight with an increase in HDL-cholesterol after 6 months of carbohydrate reduction. However, there is a U-shaped curve for total and LDL-cholesterol at 6 months, suggesting that low intakes of carbohydrate with the consequent increase in animal protein and fat could have detrimental effects on cardiovascular health. In addition, the benefit observed for body weight at 6 months was lost at 12 months, suggesting that adherence to a low-carb diet is difficult to sustain in the longer term.
The study solidifies what we already know, that lowering carbohydrates in the diet may be of use for short term control of cardiometabolic risk factors and glucose regulation but to the detriment of LDL-cholesterol levels. Ideally, protein and fat should be obtained from plant rather than animal sources if considering this approach in the longer term.
KETO VERSUS MED DIET: This randomised crossover trial compared a ketogenic (keto) diet with a Mediterranean (Med) diet for diabetes control as evidence by HbA1c levels in people with prediabetes and type 2 diabetes. The study included 40 participants with data available on 33 for the final analysis. For the first 4 weeks of each phase participants were provided their food and meals for free. Both diets were quite healthy and shared in common the incorporation of non-starchy vegetables and avoidance of added sugars and refined grains. The main differences being the Med diet was higher in fruit, whole grains and legumes, whilst the keto group avoided these foods. Calorie restriction was not required with participants instructed to eat to satiety. The keto diet aimed to restrict carbohydrate consumption to 20–50g per day. The Med diet was mainly plant-based with the exception of fish. The study also measured other markers of cardiometabolic health.
After 12 weeks on each diet, the results showed that both diets were able to equally reduce HBA1c levels with the keto diet showing a greater reduction in triglyceride levels. However the keto diet also showed an increase in LDL-cholesterol levels, whereas the Med diet lowered LDL-cholesterol. As expected, whilst on the keto diet the participants had higher intakes of selenium, vitamin B12 and D, whereas the Med diet phase had higher intakes of fibre, iron, folate, magnesium, thiamine and vitamins B6, C and E. Adherence to the specified diet was lower during the keto phase compared to the Med diet phase.
The authors conclude that although both diets improved glucose control to a similar degree, ‘the rise in LDL-cholesterol, decrease in fibre intake and greater potential for nutrient deficiencies on the keto diet may be concerning…..Collectively, these comparative outcomes do not support a benefit sufficient to justify avoiding legumes, whole fruits, and whole intact grains to achieve the metabolic state of ketosis’.
Overall, from the two studies discussed it can be concluded that low-carb diets can be useful for short-term control of glucose in people with diabetes, but in the longer term it may be difficult to adhere to this way of eating and this may be to the detriment of cardiovascular health given the consistent and reproducible elevation in LDL-cholesterol.
DIET AND OSTEOARTHRITIS: Osteoarthritis (OA) is very common and often considered an inevitable consequence of ageing. However, there are some data to suggest that healthy diet patterns such as the DASH (Dietary Approaches to Stop Hypertension) and Mediterranean diets may be protective. It is thought that this may be due to the abundance of plant foods, high in phytochemicals, in these diet patterns. Phytochemicals are natural non-nutritive bioactive compounds including polyphenols (phenolic acids, isoflavones, curcuminoids, flavonoids, terpenoids, lignans, stillbenes, and calcones), organosulfurs, and phytosterols, which have anti-oxidant and anti-inflammatory properties.
This case-control study from Iran included 248 participants with a median age of 49 years and a median BMI of 28. The impact of phytochemical consumption on the risk of knee OA was assessed from dietary data using the dietary phytochemical index (DPI). The results showed that participants with OA had a lower consumption of fruit, vegetables and olive oil compared to controls. After adjustment for potential confounders, such as BMI and physical activity, participants with a higher DPI had a 65% reduction in the odds of having knee OA, with a stronger association in males than females.
This is definitely not the most robust study design as it only assesses participants at one point in time. It can not demonstrate cause and effect but is hypothesis generating. We already have a small randomised study using a whole food plant-based diet in people with OA, which found improvements in pain and functionality in those on the plant-based diet. Definitely no downside of a plant-rich diet and there may be benefits for preventing OA too.
GINGER AND HUMAN HEALTH: I don’t usually cover studies of individual foods/supplements as the overall diet pattern matters most. However, the consumption of ginger does appear to have unique benefits, including anti-inflammatory, antioxidant, and antiemetic effects, as well as lowering blood pressure, blood lipids, and blood glucose and reducing pain. This umbrella review brings together data from 24 systematic reviews of clinical trials to assess the therapeutic impact of ginger consumption on human health. Overall, the analysis showed the following;
· In females with dysmenorrhea, there was consistent evidence that ginger statistically significantly reduced pain severity but not pain duration compared with placebo and is as effective as non-steroidal anti-inflammatory drugs.
· In participants with osteoarthritis, there was a large body of consistent evidence that ginger statistically significantly reduced pain severity and pain-related disability compared with placebo.
· In participants with headache or migraine, meta-analyses found no statistically significant effect of ginger on treatment response compared with placebo.
· There is consistent evidence of a moderate to large beneficial effect for cardiovascular health, glycaemic control, and weight management. This included lowering of systolic and diastolic blood pressure, reduction of total cholesterol and triglycerides and increase in HDL-cholesterol. Regarding glucose control, 0.05–3 g/d for 2–3 month led to a 1% reduction in HBA1c which is clinically meaningful.
· In pregnant women, there was consistent evidence that ginger statistically significantly reduced nausea incidence and severity when compared with placebo. Women consuming ginger being 7.5 times less likely to experience nausea than those who received placebo
· There was consistent evidence that ginger led to a reduction in blood markers of inflammation.
· There was weaker evidence that ginger reduced postoperative nausea and chemotherapy-induced vomiting.
· Most primary studies included multiple forms of ginger consumption, but the best evidence was for ginger capsules. Doses of 0.5–3.0 g/d in capsule form administered for up to 3 months duration was found to be optimal across most outcomes.
· The most commonly reported side-effects, regardless of study population, were mild gastrointestinal side effects, mainly reflux or heartburn abdominal discomfort, and diarrhoea. In addition, ginger may not be suitable for those with platelet disorders as studies have found ginger to reduce platelet aggregation, especially in those taking blood-thinning medications.
The authors conclude ‘Dietary consumption of ginger appears safe and may exert beneficial effects on human health and well-being, with greatest confidence in antiemetic effects in pregnant women, analgesic effects in osteoarthritis, and glycaemic control’.
CLIMATE AND HEALTH, ALL OUR HEALTH: Timely and relevant new guidance for health professionals from the UK government acknowledging that the climate crisis is a health crisis and calling the profession to take action. Lots of good information. It is clear that what is good for the planet is also good for our personal health.
For the first time there is also support for a shift to a more plant-based diet with an emphasis on plant sources of protein instead of animal sources.
‘Our current food system is a major contributor to global temperature rise, deforestation, biodiversity loss, freshwater overextraction, as well as air and plastic pollution. At the same time, the way we eat is causing significant morbidity and mortality, with poor diets increasing the risk of heart disease, high blood pressure, type 2 diabetes, obesity and certain cancers. Diet-related ill health is estimated to cost the NHS and wider UK society £5.1 billion per year, having a higher impact on the NHS budget than smoking, alcohol consumption and physical inactivity.
The foods most damaging to our health are often those with the highest emissions, pollution, land and water use. A diet rich in plant-based foods, and lower in animal source foods which have a significant environmental impact, has benefits for health and the environment. Adherence to the Eatwell Guide which encourages a high consumption of fruits, vegetables, wholegrains and plant-based protein, could contribute to a 7% reduction in mortality and a 30% reduction in greenhouse gas emissions.’
This finally feels like progress from the Government. However, it is not clear that this will lead to action it terms of changes in legislation or policy. Despite the bold recommendations for transformation of our farming system with significant reduction of meat consumption and increased fruit and vegetables consumption in the National Food Strategy, it has been suggested that plans for implementation will be greatly watered down allowing for ‘business as usual’.