Nutrition, Immunity and COVID-19

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Our immune system protects us from pathogens like viruses, bacteria, cancerous cells, etc. and it can be separated into 2 distinct branches: the innate immune system and the adaptive immune system. Our innate immune system uses cells such as macrophages, neutrophils and mast cells to mount a fast, generic response to pathogens. Inflammation is the hallmark of the innate immune system. On the other hand, the adaptive immune system uses T cells, B cells and natural killer cells to mount a slow, targeted response to pathogens. It’s the adaptive immune system that’s responsible for life-long immunity to certain diseases. In practice, the 2 branches interact to provide a comprehensive immune response.

In a recent article, Butler and Barrientos (2020) summarised the interactions between diet, immunity and COVID-19. They state that the typical western diet (high in saturated fats, refined carbohydrates and sugars, and low in fibre, unsaturated fats and antioxidants) “significantly impairs adaptive immunity while ramping up innate immunity, leading to chronic inflammation and severely impairing host defence against viral pathogens.

The authors note that “T and B cell counts were also significantly lower in patients with severe COVID-19; thus, there could be a potential interaction between western diet consumption and COVID-19 on adaptive immunity impairment.” They suggest the higher rates of obesity and diabetes among ethnic minority populations may partly account for the health disparities seen in response to COVID-19.

Butler and Barrientos conclude “that individuals refrain from eating foods high in saturated fats and sugar and instead consume high amounts of fibre, whole grains, unsaturated fats, and antioxidants to boost immune function.”

Early Feeding Improves Pre-Diabetes and Blood Pressure

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About a year ago Sutton et al. published a study that showed that intermittent fasting has benefits that are independent of food intake and weight loss. Their trial tested the effects of 5 weeks of “early time-restricted feeding” (eTRF) on 8 men with pre-diabetes. The subjects were asked to start breakfast between 6:30-8:30 and to eat their 3 meals in a 6-hour window with dinner before 15:00. They were fed enough food to maintain weight. The control group had similar meals but within a 12-hour feeding window. Five weeks of eTRF significantly improved insulin levels, insulin sensitivity, blood pressure and oxidative stress levels. The blood pressure improvements were particularly dramatic – morning levels of both systolic and diastolic blood pressure were reduced by about 10 mm Hg each.

Some of the benefits of eTRF are believed to originate from eating in alignment with our internal biological clocks which are primed for feeding early in the day. The authors state that “in humans, insulin sensitivity, beta cell responsiveness, and the thermic effect of food are all higher in the morning than in the afternoon or evening, suggesting that human metabolism is optimized for food intake in the morning”. Fortunately eTRF lowers the desire to eat in the evening!

Meal Times Crucial For Weight Loss

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A few months ago Lopez-Minguez et al. reviewed studies looking at the effect of meal times on obesity and metabolic risk. Their findings are summed up in the following points:

  • skipping breakfast is linked to obesity
  • eating a large breakfast (within 2hrs of waking) decreases the probability of being obese by 50%
  • a late lunch (after 3pm) hampers weight loss and has a negative effect on the diversity and composition of our microbiota
  • a late dinner (less than 2hrs before bedtime) decreases glucose tolerance
  • eating a large, late dinner (less than 2hrs before bedtime) leads to a 5-fold increase in the risk of becoming obese
  • the timing of breakfast seems to be hereditary whereas the timing of dinner is mainly cultural

There may be some truth in the following quote by Adelle Davis.

Eat breakfast like a king, lunch like a prince and dinner like a pauper

As well as getting the timing right obviously!

Excess Dietary Salt Leads To Cognitive Impairment

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Faraco et al. recently discovered mechanisms by which salt-rich diets can lead to cognitive dysfunction in mice. An increase in dietary salt led to a deficiency of nitric oxide in cerebral blood vessels. As nitric oxide is a vasodilator, the reduced levels resulted in decreased cerebral blood flow. In addition, nitric oxide deficiency causes the distortion of a brain protein (tau) which affects the structure and function of nerve cells. The authors conclude that the “avoidance of excessive salt intake and maintenance of vascular health may help stave off the vascular and neurodegenerative pathologies that underlie dementia in the elderly.”

Paleo Diet May Be Bad For Cardiovascular Health

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Research published earlier this month in the European Journal of Nutrition questions the health benefits of the Paleolithic diet. The Paleo diet claims to mimic the diet of our ancestors. It’s high in meat, fruits, vegetables, nuts and seeds but avoids dairy, legumes and grains.

Genoni et al. studied a group of about 100 people over a year. Half the group followed a Paleo diet and the rest followed a diet typical of national recommendations. The authors found that there was a significant difference in the gut bacteria between groups, with an increased presence of Hungatella in the paleo group. Hungatella produces trimethylamine-N-oxide (TMAO), a gut-derived metabolite associated with cardiovascular disease. Consequently the levels of TMAO were higher in the Paleo group and this was inversely associated with whole grain intake.

The authors conclude that “although the Paleo diet is promoted for improved gut health, results indicate long-term adherence is associated with different gut microbiota and increased TMAO. A variety of fiber components, including whole grain sources may be required to maintain gut and cardiovascular health.”

Higher Fibre Intake Improves Health

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Last month Reynolds et al. published an article in The Lancet that looked into the relationship between carbohydrate quality and health. They carried out a series of systematic reviews and meta-analyses that evaluated around 135 million person-years of data from 185 prospective studies as well as 58 clinical trials with 4635 adults. They found that those with higher intakes of fibre had lower body weight, lower systolic blood pressure and lower total cholesterol. Those with higher fibre intakes also had a decreased incidence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer, which may explain the 15-30% decrease in all-cause mortality between the groups with high and low fibre intake. Daily intake of fibre between 25g-30g seemed to confer the greatest risk reduction, although they note that “higher intakes of dietary fibre could confer even greater benefit“.

Low Carbohydrate Diets Are Bad For Health

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Yesterday professor Banach, from the Medical University of Lodz in Poland, released the findings of his research at the European Society of Cardiology. The prospective study looked at the relationship between low carbohydrate diets, all-cause mortality and deaths specifically from coronary heart disease, stroke and cancer. The study group consisted of almost 25,000 adults from the US National Health and Nutrition Examination Survey (NHANES) from 1999 to 2010. Over an average 6.4-year follow-up, compared to the group with the highest consumption of carbohydrates, the group with the lowest consumption had an increased risk of all-cause mortality (32%) and an increased risk of death from coronary heart disease (51%), stroke (50%) and cancer (35%). These results were backed up by the findings of a meta-analysis of several studies involving close to 450,000 people.

Professor Banach said: “Low carbohydrate diets might be useful in the short term to lose weight, lower blood pressure, and improve blood glucose control, but our study suggests that in the long-term they are linked with an increased risk of death from any cause, and deaths due to cardiovascular disease, cerebrovascular disease, and cancerThe reduced intake of fibre and fruits and increased intake of animal protein, cholesterol, and saturated fat with these diets may play a role. Differences in minerals, vitamins and phytochemicals might also be involved. Our study highlights an unfavourable association between low carbohydrate diets and total and cause-specific death, based on individual data and pooled results of previous studies. The findings suggest that low carbohydrate diets are unsafe and should not be recommended.

Plant-Based Diets Improve Health

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Last month “Nutrition 2018” was held in Boston. It was the inaugural flagship meeting of the American Society for Nutrition. Evidence from several studies was presented showing that a primarily plant-based diet is linked to numerous health benefits. Obviously, the quality of the food was important as well. Here is a summary of 5 papers that were presented:

  • A 13 year study of 6000 people in the Netherlands found that a higher proportion of dietary plant protein to animal protein was linked to lower risks of developing heart disease.
  • A study of 4500 Brazilians showed that those eating more plant-based protein were 60% less likely to have coronary artery plaque than those consuming more animal-based protein.
  • South Asians living in the US that followed a vegetarian diet had a lower number of risk factors for heart disease and diabetes (lower body mass index, smaller waist circumference, less abdominal fat, lower cholesterol levels, lower blood sugar levels) than those that ate meat.
  • A 4-year American study of over 125,000 adults showed that a whole food plant-based diet (whole grains, fruits, vegetables, nuts, etc.) led to less weight gain than a processed plant-based diet (sweets, refined grains, fries, etc.).
  • A study on 30,000 American adults demonstrated that improving the quality of the plant-based component of diet decreased mortality by 30% whereas improving the quality of the animal-based components had little effect. Among people with chronic health problems these beneficial effects were even more pronounced.

These recent research findings add to the mounting body of evidence supporting the health benefits of a whole food plant-based diet.

Plant-Based Diets Prevent Obesity

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Zhangling Chen et al., from Erasmus Medical Centre in the Netherlands, presented new research on diet at this year’s European Congress on Obesity. Their findings were based on a long-term study observing around 10,000 middle-aged and elderly adults from the Rotterdam Study. The results showed that people eating a higher proportion of plant-based foods have lower waist circumferences and BMIs, mainly due to lower body fat mass.

As we already know, obesity is associated with elevated levels of inflammation and greater risks of getting “diseases of affluence” such as diabetes, heart disease, stroke, cancer and osteoarthritis.

According to the authors: “a more plant-based and less animal-based diet beyond strict adherence to vegan or vegetarian diets may be beneficial for preventing overweight/obesity in middle-aged and elderly populations. In other words, eating to protect against obesity does not require a radical change in diet or a total elimination of meat or animal products. Instead, it can be achieved in various ways, such as moderate reduction of red meat consumption or eating a few more vegetables. This supports current recommendations to shift to diets rich in plant foods, with low consumption of animal foods.” This conclusion is reassuring and encouraging for all those that would like to make some dietary changes but are intimidated by the effort and motivation required to completely overhaul their diets. We have to start our journey somewhere…and just a few steps in the right direction can start to make a difference!

Fibre Helps Treat Osteoarthritis By Decreasing Inflammation

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It’s well-known that obesity can cause or exacerbate osteoarthritis (OA) through excessive mechanical loading. But another mechanism through which obesity can affect joint health is via inflammation and we now know that our gut microbes play a crucial role.

Recent research by Schott et al. has looked into the link between obesity, gut microbes and OA. They found a difference between the types of gut bacteria in obese mice compared to lean mice. The obese mice had more pro-inflammatory and fewer anti-inflammatory species than lean mice. The imbalance led to accelerated knee OA due to systemic inflammation and macrophage migration to the synovium. Interestingly, they found that oligofructose, a non-digestible prebiotic fibre, can help restore a normal lean gut microbiota in obese mice. The restoration of lean gut microbes was “associated with reduced inflammation in the colon, circulation and knee and protection from OA”.

Obviously one could wonder whether these findings apply to humans. About a year ago Dai et al. published the results of long-term studies on around 6000 people. Their findings consistently showed that higher total fibre intake was related to a lower risk of getting symptoms of knee OA!