Review of the week’s plant-based nutrition news 23rd May 2021
This week I cover the impact of salt consumption on blood pressure, plant-based diets for kidney disease, healthy lifestyle and risk of colorectal cancer and attitudes to factory farming and pandemic risk.
SALT CONSUMPTION AND BLOOD PRESSURE: There is sometimes confusion in the literature about the impact of salt consumption on health outcomes. The WHO recommends no more than 5g/day (2g of sodium). Analysis from the PURE study caused controversy by calling these recommendations into question as the results suggested that salt consumption was not such a problem after all and in fact consuming less than 11g/day was associated with harm. These data have been disputed by a number of reputable authorities.
One of the main ways in which salt consumption impacts health outcomes is through elevation of blood pressure (BP) and thus an increased risk of cardiovascular disease. This current study is a very useful meta-analysis that includes 85 intervention studies that report impact of dietary changes in salt consumption on BP. The trials were conducted in participants with hypertension (n=65), without hypertension (n=11), or a combination (n=9) and had a follow up of of 4–36 months. A dose-response analysis was also conducted.
The results clearly show a linear, dose-response relationship between salt consumption and BP. Salt restriction was able to reduce BP in people with and without hypertension, having a greater impact on those with elevated BP. There was no threshold at which the impact was no longer apparent with intakes as low as 1–1.5g/d of sodium continuing to result in a lower BP. The impact on systolic BP was greater than diastolic.
In participants without hypertension, a sodium intake of 6g/d compared with 2g/d, the mean systolic BP and diastolic BP increased by 3.99 mm Hg and 1.66 mm Hg respectively. In participants with hypertension, the differences were 10.31 mm Hg and 5.13 mm Hg. In the dose-response analysis, in participants without hypertension, a 100 mmol/d (2.3g) decrease in sodium intake was associated with a reduction in mean systolic BP and diastolic BP of 2.30 mm Hg and 0.80 mm Hg, respectively. The corresponding systolic BP and diastolic BP reductions in participants with hypertension were 6.5 mm Hg and 3 mm Hg.
These are pretty impressive results. The average salt intake in the UK is around 8g/d (3.1g sodium). A blood pressure reduction of 4mm Hg can get a drug for hypertension licenced. These data support the ongoing recommendations to limit added salt in the diet. In fact, excess salt consumption was identified as the leading dietary risk factor causing death globally (responsible for 3 million deaths annually) in 2017 and this is a reflection of our reliance on processed and pre-prepared supermaket foods and meals eaten outside the home. Hypertension is a leading risk factor for death and disability globally. On a whole food plant-based diet you get all the salt you need. Adding a small amount to a healthy plant-based diet is unlikely to be a major problem, although not necessary. Plant-based diets are associated with a greatly reduced risk of hypertension.
FRUITS AND VEGETABLES FOR TREATMENT OF METABOLIC ACIDOSIS: The beneficial role of a plant-based diet for prevention and treatment of chronic kidney disease has really come into its own in the last couple of years, with an increasing number of supportive publications.
This study brings us longer, 5 year follow-up of a previously reported analysis. The study investigated whether fruit and vegetable consumption could be as effective as sodium bicarbonate tablets in people with renal failure and metabolic acidosis. Both these intervention groups were compared to a usual care group that did not receive any treatment to reduce acid load, with 36 participants in each of the 3 groups. The fruits and vegetables were provided free of charge, including enough for family members. The emphasis was on fruits and vegetables that are base-forming and included fruits predominantly as apples, apricots, oranges, peaches, pears, raisins, and strawberries and vegetables predominantly as carrots, cauliflower, eggplant, lettuce, potatoes, spinach, tomatoes, and zucchini.
The results showed no difference in acid load between the 2 intervention groups with improvement shown in metabolic acidosis in both groups. This was compared to a worsening in acidosis in the usual care group. There were however additional advantages for the fruit and vegetable group, including lowering of BP and cholestorol medication dosage and a lower rate of cardiovascular events (although numbers are very small). These benefits translated into lower medical costs for the fruit and vegetable participants due to lower medication costs and lower number of hospitalisations.
These are very compelling data for the use of ‘food as medicine’. A number of excellent reviews have been written on plant-based diets for chronic kidney disease, including this guide for health professionals.
PLANT-BASED DIETS IN HAEMODIALYSIS: This freely accessible review article is very welcome and well worth reading. In general, clinicians have been wary about prescribing plant-based diets for people on dialysis. The concerns relate to the higher potassium and phosphate and lower protein content of plant foods. But these concerns are no longer valid when reviewing the scientific literature and in fact the potential benefits vastly outweigh these more theoretical concerns.
The review paper summarises the potential benefits of plant-based diet in this clinical setting. These include a reduction in systemic inflammation due to the abundance of phytochemicals with antioxidant and anti-inflammatory effects. This is in addition to removing inflammatory animal-derived foods from the diet. The higher fibre intake reduces the level of uraemic toxins, prevents constipation, helps facilitate excretion of potassium and promotes a healthier gut microbiome. Plant-based proteins have been shown to be adequate in quality and quantity in this patient population. There are also the co-benefits for reducing the risk and impact of other co-morbidities that may also be driving the kidney failure such as hypertension, type 2 diabetes and cardiovascular disease.
Plant-based diets for prevention and treatment for kidney failure are now mainstream. Let’s start supporting our patients to make these healthy choices.
LIFESTYLE, GENETICS AND COLORECTAL CANCER (CRC): CRC is the third commonest cancer and 4th leading cause of cancer death globally with the burden expected to increase by 60% to more than 2.2 million new cases and 1.1 million cancer deaths by 2030. Yet around more than 50% of cases could be prevented by addressing common risk factors: eating too little fibre, red and processed meat consumption, obesity, tobacco smoking and alcohol consumption. There are of course some individuals who have a higher genetic risk of CRC and this study assesses the impact of healthy lifestyle factors in people with different genetic risk.
The study used data from 346,297 participants in the UK Biobank cohort. Healthy lifestyle scores (HLSs) were constructed using 8 lifestyle factors, according to the American Cancer Society guidelines, and were categorized into unhealthy, intermediate, and healthy groups. These lifestyle factors were BMI (kg/m2), waist-to-hip ratio (WHR), physical activity, sedentary time, processed and red meat intake, vegetable and fruit intake, alcohol consumption, and tobacco smoking. A polygenic risk score (PRS) was created using 95 genetic risk variants. During the 5.8 years of follow-up there were 2066 new cases of CRC.
The results showed that a high HLS was associated with a significantly lower risk of CRC and there was a dose effect. In addition, the reduction in risk was greater in those with a higher PRS. This risk reduction was in the order of 30–50%. The greatest individual risk factors were higher WHR, consumption of red and processed meat, alcohol consumption and tobacco smoking.
Once again, your genes are not your destiny. We talk about personlised medicine for cancer treatment, but the authors conclude that we need to ‘establish personalized preventive strategies for cancer prevention’. These same healthy lifestyle factors are just as important after a diagnosis of CRC as they can help increase the length of remission and survival following treatment.
FACTORY FARMING AND FUTURE PANDEMICS: I am grateful that scientists are sounding the alarm on the hazards of our current food system. This is a topic that has not had enough airtime since the start of the pandemic. Rather than address the root cause of pandemic infections, virtually all resources are being put into early warning and detection systems. Yet we could vastly reduce the risk of future pandemics by changing our food system. Raising animals for food is the main driver for generating new infections with epidemic and pandemic potential.
The paper starts with this poignant quote ‘We are preoccupied with the production of face masks, but we appear unconcerned with the farms that are producing pandemics. The world is burning and we are reaching for more fire extinguishers while gasoline soaks through the tinder at our feet.’ (Foer & Gross, 2020).
The paper reports on two cross-sectional studies from the UK started early in this current COVID-19 pandemic. The first examined whether people recognised the threat of future pandemics from factory farming. The second sought to understand whether people would support the changes required to prevent future pandemics i.e. dietary change.
The first study included 302 participants and found that people blamed wildlife animal trade and consumption more than factory farming and global meat consumption for future pandemic risk and were less supportive of solutions to end factory farming than those solutions aimed at better preparing and equipping society to combat infectious diseases. Those most committed to meat consumption were more likely to downplay the importance of factory farming in pandemic risk. In the second study, 201 participants were provided with information on the risk of pandemics from the wildlife trade and factory farming. Despite the strong link between factory farming and pandemics, participants were more supportive of measures to curb the wildlife trade than interventions to limit or abolish factory farming. Again the attitudes were dependent on the participants commitment to meat consumption.
The authors conclude ‘Our findings are arguably consistent with research on “solution aversion”, whereby people exhibit motivated skepticism about the existence of a problem, not necessarily because of an aversion to the problem itself but because the associated solutions are threatening to personal or ideological motives.’ This is indeed very sad to read as we have the solutions to so many of our current global problems, yet are unwilling to act when it jeopardises our own personal choices. This is an excellent report from ProVeg laying bare the facts around animal farming and the generation of pandemics.
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