A review of the week’s plant-based nutrition news 2nd August 2020
This week I cover two large reports on prevention of dementia and studies that support plant-based diets for managing risk factors for dementia.
LANCET COMMISSION ON DEMENTIA 2020: The rising burden of dementia is a global problem and its impact in the coming decades is going to be felt more in low and middle income countries. Worldwide around 50 million people live with dementia, and this number is projected to increase to 152 million by 2050. This is an updated report from the Lancet commission, the first published in 2017. Now 12 potentially modifiable factors are thought to be important in preventing or delaying the onset of dementia. These combine socioeconomic and lifestyle factors throughout the lifespan. The 3 new risk factors are excessive alcohol consumption, air pollution and traumatic brain injury. This is in addition to 9 risk factors identified in the 2017 reports; diabetes, obesity, hypertension, smoking, lack of physical activity, depression, hearing impairment, low educational attainment and social isolation. Together it is thought that these 12 potentially modifiable factors could prevent or delay up to 40% of cases of dementia.
It should be noted that the studies informing these recommendations are mostly performed in high income countries, whereas the burden of dementia is greater in low and middle income countries and therefore the potential for prevention may be even greater.
Other contributing factors discussed in the current report include good quality sleep and diet. Regarding diet, the focus of researchers has turned more to diet patterns rather than individual nutrients. High intake of whole plant foods is what the paper recommends. Data supporting the Mediterranean diet pattern is strongest because of the high consumption of fruits, vegetables, cereals, nuts, legumes and olive oil with low intake of saturated fats and meat. Interestingly the report does not even mention fish consumption. There is no strong evidence for use of supplements although nutrients such as folate, B vitamins, vitamin C, D, E and selenium should be optimised, ideally through the diet.
Another interesting observation made is that cognitive reserve i.e. preservation of cognition or everyday functioning, can be increased or maintained despite the presence of brain pathology and neuropathological changes associated with dementia. Early-life factors, such as less education, affect the resulting cognitive reserve. Midlife and old-age risk factors influence age-related cognitive decline and triggering of neuropathological developments.
To really be affective, these recommendations require social and behavioral interventions. In high income countries, the risk factors described are more prevalent in communities of lower socioeconomic means and in ethics minorities. High level of education, healthy diets, open space for physical activity, reduction in air pollution and equal access to healthcare for example will require high level policy implementation with Government support. The UK has recently instituted an innovative programme of social prescribing, which enables primary care doctors to refer patients to non-clincial services in the community that may help address some of the risk factors described in this report. Examples of social prescribing include arts activities, group learning, gardening, befriending, cookery, healthy eating advice and a range of sports.Time will tell us whether this more holistic approach to healthcare can impact the risk of chronic diseases such as dementia.
This Lancet report carries a positive message in that preventing and delaying the onset of dementia may indeed be possible. But the enormity of the task is apparent given how social and structural inequalities in life experiences and opportunities play such a large role.
MODIFIABLE RISK FACTORS AND INTERVENTIONS FOR PREVENTION OF ALZHEIMER DISEASE (AD): This is a massive paper that brings together data from 243 observational prospective studies and 153 randomised controlled trials. With the data, authors compile a list of potentially modifiable risk factors and interventions that could significantly reduce the risk of AD. I fully accept that not all of the risk factors are within an individuals control and socioeconomic and environmental factors have an important and related role to play.
The overarching theme is one of taking care of your cardiovascular health. Eight risk factors (diabetes, orthostatic hypotension, hypertension in midlife, head trauma, stress, depression, midlife obesity and coronary artery bypass grafting (CABG) surgery)and three protective factors (maintaining cognitive activity, increased BMI in late life and higher level of education) had the strongest association with the risk of AD. It is interesting that being too thin in later life may be detrimental to brain health. This may reflect reverse causation in that lower body weight is associated with frailty and chronic conditions that predispose to fraility as we age. Thus the best approach is to maintain a healthy weight throughout life aiming for a BMI around 20–23.
Other important factors included sleeping well and avoiding smoking. Eating a healthy diet plays an important role, with particular emphasis on vitamin C and B vitamins and folate to keep homocysteine levels within normal range. Thus diet for dementia prevention centres around eating plenty of fruits and vegetables and if you are consuming a 100% plant-based diet, supplementing with B12 is essential. Avoiding frailty with aging is key and important factors include a healthy plant-predominant diet pattern and regular physical activity, including muscle strengthening activities. There is very little evidence to support pharmaceutical interventions and medications which definitely do not help prevent AD include oestrogen replacement and acetylcholinesterase inhibitors.
This report contains more risk factors and recommendations than the Lancet commission, which only includes those with the highest level of evidence. Whereas, this report highlights risk factors where strength of evidence is less certain. The key with brain health is that preventative measures need to start early in life and experiences and risk factors from birth through to older age play their part.
PLANT-BASED DIETS FOR TYPE 1 DIABETES: We are now becoming familiar with the evidence for plant-based diets for prevention, management and potentially reversal of type 2 diabetes. In fact, just a few weeks ago I highlighted a position statement from the American College of Lifestyle Medicine on the optimal diet for prevention and reversal of type 2 diabetes, and it is one centred predominately around whole plant foods. So what about type 1 diabetes? Is there are role for plant-based diets? The conventional wisdom is that because type 1 diabetes is an autoimmune disease in which insulin production is absent, dietary approaches tend not to be so important. Most patients are counselled to limit carbohydrate intake in order to reduce insulin requirements and keep blood sugar levels more steady. However, there are increasing, albeit anecdotal, reports of patients with type 1 diabetes benefiting from a plant-based diet, with significant reductions in insulin requirements and of course the co-benefits for cardiovascular health. It is therefore exciting to read the highlighted case reports on plant -based diets for type 1 diabetes, and no surprise that Dr Neal Barnard is once again leading the way. However, this is not the first report I have seen and this case report from India was published in 2019.
The current report highlights two cases of type 1 diabetes in which the patients switched to a plant-based diet. In the first case, the patient at diagnosis was consuming about 150 g of carbohydrates per day and was taking 50–60 units total per day of insulin, about 60% of which was long-acting. After the diet change, he was consuming 400 g-450 g of carbohydrates per day in the form of whole, unprocessed fruits, vegetables, and grains and required 26 units total of insulin per day, his weight dropped from 190 lbs to 180 lbs with HbA1c control in the longer term ranging between 5.5%-5.8%. In case 2 the patients was orginally eating a low-carbohydrate diet, high in fat and animal foods. She noticed better blood sugar control but an increased requirement for insulin per gram of consumed carbohydrate. However, her HbA1c did decrease to 5.6%. Despite this she saw a rise in blood cholesterol levels. This prompted a change to a plant-based diet, which significantly reduced insulin requirements and brought down her blood cholesterol levels, whilst maintaining a good HbA1c level. Both patients experienced episodes of hypoglycaemia in the first few days to weeks.
These cases reveal that patients with type 1 diabetes also have a degree of insulin resistance, which is reversed on a plant-based diet. Insulin resistance is caused by the accumulation of fat inside muscle and liver cells. The primary driver for this is a diet high in animal-derived foods and processed foods. A plant-based diet has been shown to be very effective at restoring insulin sensitivity and in type 2 diabetes at least may even restore some beta cell pancreatic function. Nonetheless, for the wider medical community to take this onboard in the context of type 1 diabetes, randomised control trials will be needed. In the meantime, the norm seems to be the recommendation for low carbohydrate diets as discussed in this recent editorial in BMJ evidence-based medicine. I agree that the short term impact on blood sugar control is compelling but the negative longer term impact of a low-carbohydate diet, when high in animal-derived fat and protein, on heart health, cancer risk and mortality is worrying to say the least and is rather short-sighted when a plant-based diet has both short and long term benefits.
HEALTHY PLANT-BASED DIETS PREVENT HYPERTENSION: We have know for a while that vegan and vegetarain diets are useful for maintaining a healthy blood pressure (BP). The DASH diet was designed using the knowledge that the vegetarian diet was effective at lowering BP. However, we know that not all vegetarian and vegan diets are alike and observational studies on these diet patterns don’t always tell us which foods are the most useful in the diet. Hence the development and use of the plant-based diet index, which I have written extensively about previously. This allows diet data to be analysed based on the plant foods eaten with whole plant foods given positive scores whereas processed plant foods (deemed unhealthy) and animal foods given negative scores.
This large study used dietary data from 4,680 men and women ages 40–59y in Japan, China, the United Kingdom, and the United States from the INTERnational study on MAcro/micronutrients and blood Pressure (INTERMAP). The study used the plant-based diet index (PDI), healthy PDI (hPDI), and unhealthy PDI (uPDI) and modified them according to country-specific dietary guidelines for use across populations with diverse dietary patterns in order to assess their associations with BP.
The results showed that higher adherence to a hPDI, a measure of a high-quality plant-based diet, but not overall PDI, was inversely associated with systolic and diastolic BP. In contrast, a higher score of uPDI was directly associated with systolic BP. The data showed that the foods contributing most to a reduction in BP were vegetables and whole grains. Refined grains, sugar-sweetened beverages and total meat contributed the most to the positive associations of uPDI with BP. Eating one serving of whole grains and four servings of vegetables, while limiting total meat intake to 100 g per day was associated with a systolic BP lowering effect of around 4 mm Hg. It has to be remembered that to get a BP lowering medication licensed by the FDA in the US, drug companies only have to demonstrate that it lowers BP by around 4mmHg. Thankfully, whole grains and vegetables can’t be patented!
The benefits of plant foods for lowering blood pressure come from the high potassium, fibre, calcium, nitrate and low sodium content plus the unsaturated fats that contribute to better endothelial function. Once again the importance of the quality of the foods consumed is highlighted with unhealthy plant foods being just as detrimental to health as a diet high in meat.
PLANT-DOMINANT DIETS FOR CHRONIC KIDNEY DISEASE: I have highlighted a number of studies in the last year that demonstrate the benefits of a diet high in whole plant foods and low in meat, dairy and eggs for prevention and treatment of renal failure. It should be remembered that type 2 diabetes and hypertension are the main risk factors driving the rise in chronic kidney disease and both conditions are largely prevented and treated by adopting a plant-based diet.
The premised behind a plant-based diet for kidney health is that high protein diets with high meat intake are associated with a higher risk of kidney failure and faster progression to end stage kidney failure and the need for dialysis. This is because the protein load puts pressure on the kidneys and results in glomerular hyperfiltration. Meat intake increases production of nitrogenous end-products, worsens uraemia, and may increase the risk of constipation due to the typical low fibre intake, resulting in hyperkalaemia. High meat diets have a high acid load thus worsening the acidosis of renal failure. Animal foods have a negative impact on the gut microbiome and lead to the generation of compounds such as TMAO that adversely impact kidney function. Animal protein and fat are directly associated with the development of atherosclerosis.
The authors propose the use of a plant-dominant low protein diet (PLADO) for prevention and treatment of kidney disease. Low protein diets (0.6–0.8g/kg/day) are associated with less pressure on the kidneys. Plant foods high in fibre are associated with a reduced dietary acid load as plant foods have a natural alkali effect. The reduced intake of phosphate from plant foods is beneficial. There is less exposure to advanced glycation end products, which are associated with kidney damage. There is better potassium metabolism, anti-inflammatory and anti-oxidant effects and improvement in the gut microbiome and hence less exposure to toxins from the gut. Salt intake is also limited on the PLADO diet, although compared with WHO and American Heart Association recommendations, it still remains generous in salt.
The key to the success of such a diet approach will be the engagement of patients with and access to specialised dietitians. In addition, the medical community will require randomised studies demonstrating safety and efficacy before widespread adoption. Nonetheless, it is encouraging that plant-dominant diets are commonly being discussed amongst the renal community and encourageed by patient support groups.
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