A review of the week’s plant-based nutrition news 20th February 2022
This week I cover the impact of food choices on life expectancy, gut health and vitamin D on COVID-19 outcomes, vitamin D supplements and autoimmune disease and the role of plant foods for kidney health.
FOOD CHOICES AND LIFE EXPECTANCY: Good news! Our food choices really can add years to life. Sadly, unhealthy diets remain the leading cause of death and disability globally, with an estimated 1 in 4 deaths due to an unhealthy diet, including a third of all premature deaths in Europe and the US. In this new study, researchers used existing meta-analyses and data from the Global Burden of Diseases study to build a model that enables the instant estimation of the effect on life expectancy (LE) of a range of dietary changes. Based on prior data, an optimal diet was considered to be higher intakes of whole grains, legumes, fish, fruit, vegetables, and included a handful of nuts, while reducing red and processed meats, sugar-sweetened beverages, and refined grains.
The optimal diet was similar to the the Eat-Lancet Planetary Health Plate and included the following quantities of various foods per day. Whole grains 225g (fresh weight) or 75g (dry weight), vegetables 400g, fruit 400g, nuts 25g, fish 200g, eggs 25g (half an egg), dairy 200g, refined grains 50g, red and processed meat 0g, white meat 50g, sugar sweetened beverages 0g, oils 25g.
The results showed that a sustained change from a typical Western diet to the optimal diet from age 20 years was estimated to increase life expectancy by 10.7 years in women and 13 years in men. The largest gains were shown to occur by eating more legumes (females: 2.2 years; males: 2.5 years), whole grains (females: 2.0; males: 2.3 years), and nuts (females: 1.7 years; males: 2.0 years) and less red meat (females: 1.6; males: 1.9 years) and processed meat (females: 1.6 years; males: 1.9 years). Changing from a typical diet to the optimal diet at age 60 years was estimated to increase LE by 8.0 years for women and 8.8 years for men, and 80-year-olds would gain 3.4 years. Even a half way transition towards an optimal diet was predicted to increase LE by 6.2 years for 20-year-old women from the United States and 7.3 years for men. Results were presented based on US data but similar trends were found when considering data from China and Europe.
The authors conclude ‘sustained change from a typical to an optimised diet from early age could translate into an increase in LE of more than 10 years’. Of note, a previous report from the Nurses’ Health Study and Health Professionals Follow-Up study has shown that the extra years derived from healthy diet and lifestyle habits are spent in good health rather than chronic ill health.
The model used in the study is also now available as a publicly available online tool called the Food4HealthyLife calculator (https://food4healthylife.org/).
GUT MICROBIOME AND COVID-19 OUTCOMES: I have been following with great interest the studies on diet, nutrition and COVID-19 outcomes. My summary articles can be found here (make sure you scroll down for recent updates). One of the first observations to emerge was that the health of the gut microbiome may affect severity of COVID-19, but whether this is causally related or a bystander effect still needs to be elucidated.
This prospective cohort study from Hong Kong investigated whether the gut microbiome contributes to persistent symptoms after the initial acute phase, defined as at least one persistent symptom 4 weeks after clearance of the SARS-CoV-2 virus. 106 people with confirmed COVID-19 were included and compared to 68 matched controls who had not had the infection. Stool samples were analysed at admission to hospital and 1 and 6 months following discharge (at the time all infected patients were admitted to hospital). The gut microbiota profile of those with and without persistent symptoms was compared. The commonest post infection symptoms were fatigue, poor memory and hair loss.
The results showed that people who developed post infective persistent symptoms had a distinct gut microbiota profile on admission to hospital. There was a statistically significant association with certain gut bacteria with higher levels of Ruminococcus gnavus, Bacteroides vulgatus and lower levels of Faecalibacterium prausnitzii. Persistent respiratory symptoms were correlated with opportunistic gut pathogens, and neuropsychiatric symptoms and fatigue were correlated with nosocomial (originating in hospital) gut pathogens, including Clostridium innocuum and Actinomyces naeslundii. This gut dysbiosis persisted at 6 months post infection. Hair loss was associated with the loss of butyrate-producing bacteria whereas those without persistent symptoms at 6 months had a greater abundance of butyrate-producing bacteria, including Bifidobacterium pseudocatenulatum and Faecalibacterium prausnitzii. In addition, there was an abundance of multiple bacteria known to be beneficial to immune health in those without persistent symptoms. The authors conclude ‘altered gut microbiome composition is strongly associated with persistent symptoms in patients with COVID-19 up to 6 months after clearance of SARS-CoV-2 virus. Considering the millions of people infected during the ongoing pandemic, our findings are a strong impetus for consideration of microbiota modulation to facilitate timely recovery and reduce the burden of post-acute COVID-19 syndrome’.
The good news is that a fibre-rich, polyphenol-rich plant-based diet is associated with better gut health and an abundance of bacteria that produce butyrate and other short chain fatty acids, which are essential for immune health and reduction of inflammation. No surprises, a healthy vegan diet is associated a healthy gut microbiome as evidenced by yet another paper on the topic.
VITAMIN D LEVELS AND SEVERITY OF COVID-19: We have heard a lot about the role of vitamin D in maintaining the health of the immune system during the COVID-19 pandemic, yet whether low blood levels play a causal role in the severity of infection remains to be determined. This study tries to assess the strength of this relationship by assessing the association between pre-infection serum vitamin D levels and disease severity and mortality.
Conducted in Israel, this retrospective study included 253 patients with a mean age of 63 years admitted to hospital with COVID-19 who had pre-infection levels of vitamin D available. The pre-infection levels were divided into divided four categories; deficient, insufficient, adequate, and high-normal. 133 (52.5%) had a level less than 20 ng/mL, 36 (14.2%) had 20 to less than 30 ng/mL, 44 (17.3%) had 30 to less than 40 ng/mL, and 40 (15.8%) had 40 ng/mL or greater. Based on the pre-infection values, patients with vitamin D deficiency (<20 ng/mL) were 14 times more likely to have severe or critical disease than patients with vitamin D levels of >40 ng/mL. There was a progressive decrease in levels of vitamin D as the disease severity increased. Both age and pre-infection vitamin D levels were found to be independent predictors of increased disease severity yet the association with vitamin D levels was demonstrated in all age groups (<50, 50–64, >65 years). The authors conclude ‘The use of historical results obtained before the COVID-19 pandemic as part of a public health survey enabled us to suggest vitamin D deficiency contributes to the causal pathway of COVID-19 mortality risk and disease severity’.
Of course we would prefer prospective or randomised studies to be more certain of this association but in the meantime there are plenty of reasons to make sure your vitamin D levels are in the adequate range and to appropriately supplement to ensure this is maintained. This is relevant to all diet patterns, not just plant-based diets.
MORE BENEFITS OF VITAMIN D: The VITAL study investigating the role of omega-3 fish oils and vitamin D supplementation has many components, including the Autoimmune Disease Prevention ancillary study. In this study, 25, 871 participants were enrolled and followed for a median of 5.3 years. There were 12,786 were men ≥50 years and 13 085 women ≥55 years at enrolment with a mean age of 67.1 years. 18,046 self-identified as non-Hispanic white, 5106 as black, and 2152 as other racial and ethnic groups. The intervention was Vitamin D (2000 IU/day) or matched placebo, and omega 3 fatty acids (1000 mg/day — 460 mg eicosapentaenoic acid and 380 mg docosahexaenoic acid from fish oil) or matched placebo. Of note, in the trial, these supplements were prescription grade and underwent rigorous quality testing.
The results showed that vitamin D supplementation for five years, with or without omega-3 fatty acids, reduced the incidence of all autoimmune disease by 22%. Supplementation with omega-3 fatty acids alone did not significantly lower the incidence of autoimmune disease. However, when participants with probable rather than definite autoimmune disease were included, omega-3 fatty acid supplementation did reduce the rate by 18% compared with placebo. A greater reduction in autoimmune disease was seen after 2 years of supplementation with vitamin D, with a 39% reduction in incidence in the last 3 years of the study. In addition, there was a suggestion that vitamin D was more effective at reducing the incidence of new onset psoriasis, while fish oil may be more effective at reducing autoimmune thyroid disease. A stronger effect of vitamin D was observed in those with a lower BMI compared with higher BMI, likely due to vitamin D uptake by adipose tissue and thus lower bioavailability. Interesting neither baseline serum vitamin D nor omega-3 levels were associated with outcomes from supplementation. What the study can not answer is whether these benefits will be maintained in the longer term and whether the results are applicable to younger people.
Overall, this study showed a stronger effect of vitamin D supplementation although there may be a small, additional role of EPA/DHA supplementation. Both compounds are involved in regulating inflammation and immunity. Of course, there isn’t any special about fish derived EPA/DHA but we are yet to see similar studies using algae-derived long-chain omega-3 fatty acids.
PLANT FOODS, POTASSIUM AND KIDNEY DISEASE: An excellent review by Dr Shivam Joshi and colleagues who are leading the field of plant-based nutrition in kidney disease. Once again, the paper highlights the outdated thinking around plant foods, potassium content and their role in people with kidney disease. Conventional advise has always been to avoid or reduce high potassium plant foods if high blood levels of potassium (hyperkalaemia) are a concern. However, there seems very little correlation between the potassium in plant foods and the risk of hyperkalaemia in people with kidney disease. Instead, there are numerous benefits to consuming an abundance and variety of whole plant foods.
There are a number of reasons why the potassium in plant foods don’t significantly alter blood levels. The high fibre content means less is absorbed and more is excreted in the stool, plus bowel transit is faster reducing overall potassium absorption. Fruits and vegetables are in general more alkali than animal foods, which are more acidic and this can improve metabolic acidosis i.e. keeping blood pH within normal limits. The prevention of metabolic acidosis helps keep potassium levels within normal range. In addition, the bioavailability of potassium in plant foods is generally lower than from animal foods, being around 60–70%.
The benefits of consuming more plant foods in people with kidney disease include less constipation, lower blood pressure, better glucose regulation, healthier gut microbiome, lower phosphate levels, reduced use of medications and a reduction in mortality. Benefits have even been found in those on dialysis. The authors conclude ‘We suggest a reconsideration of the previous low potassium guideline that restricts some fruits and vegetables since evidence for this is weak. The current evidence of the benefits of a healthy dietary pattern that centre plant foods should be cautiously encouraged’.