A review of the week’s plant-based nutrition news 8th August 2021
This week I cover foods that promote glucose regulation, dietary factors and the risk of non-alcoholic fatty liver disease, flavonoids and brain health and a study of the oral microbiome of our ancient ancestors.
HEALTH BENEFITS OF MILLETS: The global diet relies on just a handful of foods. Up to 70% of global calories come from rice, wheat, potato and maize. Yet we have thousands of edible plants, including a variety of so called ‘ancient grains’ that are under-utilised in human nutrition. Millet is a whole grain cereal grown in India, Africa and Asian with advantages such as being drought and pest resistant and having a low carbon footprint. There are 13 different varieties (including sorghum, finger millet, pearl millet, little millet, kodo, millet, barnyard millet, foxtail millet, proso millet, teff, fonio, and Job’s tears) with nutritional advantages such as higher amounts of of essential amino acids, calcium, zinc and iron compared to other cereals. Millet is rich in polyphenols and fibre, has a lower glycaemic index (GI) than other common grains such as rice and is also gluten free.
The current meta-analysis included 65 human studies and assessed the impact of a variety of types of millet on markers of glucose control and risk of type 2 diabetes. The results demonstrated that all varieties of millet have a lower GI than white rice and refined wheat and a similar GI index to legumes and whole wheat. Millet consumption was associated with a 12% lower fasting blood glucose level and 15% lower post-prandial glucose level compared to a wheat or rice. A millet-based diet for longer than 3 months was shown to significantly reduce HbA1c levels compared to a regular wheat or rice based diet, with around a 15% difference in levels and also to increase insulin sensitivity.
It’s not really that surprising that millets improve glucose control and insulin sensitivity when compared to refined wheat and polished rice. Whole grains in general have a number of health advantages and we should be aiming to consume 2–3 portions a day. Currently, most millet is used for animal feed. It seems we need to cut out the ‘middle man’ and starting directly consuming these ancient grains. Diversifying our diet is not only beneficial to personal health but has the potential to significantly improve the environmental and ecological health of the planet. This report from WWF lists 50 foods that we should be aiming to add to the diet for just these reasons.
GRAPES AND GLYCAEMIC RESPONSE: High fructose fruits such as grapes are often demonised as having too high a glycaemic index (GI) and thus best limited in the diet. The scientific literature does not support this narrative and virtually all studies have shown that higher consumption of fruit in general is associated with a number of better health outcomes including a lower risk of type 2 diabetes. Grapes, for example, are full of a variety of bioactive compounds including fibre, antioxidants and polyphenols
This meta-analysis of randomised studies investigated the effects of grapes and grape products (whole grapes, grape seed extract, grape juice, grape powder, grape extract, grape seed oil, and raisins) on glycaemic response including fasting plasma glucose, insulin level, haemoglobin A1C (HbA1c), and homeostatic model assessment of insulin resistance (HOMA-IR) in adults. 29 studies with 1,297 participants were included in the analysis.
Overall, the results showed that grapes and grape products reduced insulin resistance but did not affect fasting insulin levels or HbA1c levels. Grapes and their products did result in increased fasting blood glucose compared to the control group although there were only 2 studies examining the impact of the whole grape and the majority of studies used some type of grape extract such as juice, powder or grade seed extract with the consumption of juice having a greater effect on blood glucose.
Overall, studies support the consumption of a wide variety of fruits for improving physical and mental health. The evidence is strongest for improving cardiovascular health. It’s also best to stick with whole fruits consumption rather than fruit juices, which are devoid of fibre.
DIET AND FATTY LIVER: I have written many times about non-alcoholic fatty liver disease (NAFLD), a condition that did not even have a name prior to 1980 yet now affects 1 in 5 people in high-income countries such as UK and USA. Diet and lifestyle factors are critical in the prevention and treatment of the condition. NAFLD is really a metabolic condition associated with carrying too much fat, with associated insulin resistance and inflammation. There has been a call to change the name to MAFLD; metabolic-associated fatty liver disease.
This excellent review paper brings us up to date on the impact of diet on the risk of NAFLD. The key dietary components that are implicated in the development of NAFLD are high intakes of free sugar, particularly fructose, when in excess is converted to triglycerides and also stimulates the production of fat by the liver, which is then deposited in body organs including the liver. Of note, the fructose in fruits when consumed in its whole form does not result in excess generation of fatty acids and in fact fruit consumption is associated with a reduced risk of NAFLD. High intakes of saturated fat, particularly from processed and unprocessed red meat, is also implicated in causing NAFLD. One reason why saturated fat causes fatty liver is because these fats are converted into ceramides, which stimulate liver fat production, impairs mitochondrial function and causes insulin resistance.
Overall, a Western-style diet pattern high in free sugar, refined grains and saturated fat is strongly associated with an increased risk of NAFLD. In addition, the authors state that ‘high- fat–low- carbohydrate diets containing high saturated fat increase intrahepatic triglyceride (IHTG) content more than low- fat–high- carbohydrate diets’. In contrast, diet patterns that emphasise fibre-rich whole plant-foods, unsaturated sources of fat, limit intake of animal foods and processed foods, significantly reduce the risk of NAFLD. This includes the Mediterranean, DASH, vegetarian and vegan diets.
There are a number of studies supporting the role of a whole food plant-based diet for prevention and treatment of fatty liver disease. Maintaining a healthy weight is key to prevention and treatment of NAFLD and a healthy plant-based based diet is very effective at reducing calorie intake by emphasising nutrient-rich, low calorie foods. Plant-based diets are associated with less weight gain with aging and is more likely to keep you within a healthy body mass index range. A whole food plant-based diet is a very effective way of losing weight without having to emphasise portion control or calorie counting. Studies have also shown that a healthy low-fat vegan diet can normalise liver function tests and significantly reduce liver fat, whilst supporting weight loss and improving insulin sensitivity.
The senior author of this paper, Bernadette Moore, spoke at PBHP UK’s second plant-based nutrition conference in 2019. You can listen to her talk here.
DIETARY FLAVONOIDS AND BRAIN HEALTH: Diet and lifestyle factors are key to preventing cognitive decline and dementia with ageing. Healthy diet patterns that emphasise whole plant foods are associated with a reduced risk of dementia. The WHO recommends a Mediterranean diet pattern as part of dementia prevention strategies. Brain healthy diet patterns have in common an abundance of fruits and vegetables and low intakes of red and processed red meat, saturated fat, refined grains and free sugar.
This study reports data from the Nurse’s Health Study and the Health Professionals follow-up study. The study included 49,493 women with an average age of 48 and 27,842 men with an average age of 51 at the start of the study who were followed for more than 20 years. The impact of flavonoid consumption on cognitive function was assessed over time. Flavonoids are naturally occurring compounds found in plants with powerful antioxidants functions. These compounds can counteract the impact of oxidative stress and inflammation, a type of cellular stress that is associated with an increased risk of dementia.
The results showed that that people who eat a diet that includes at least half a serving per day of foods high in flavonoids like strawberries, oranges, peppers and apples may have a 20% lower risk of cognitive decline. Flavones, found in spices and yellow or orange fruits and vegetables, and anthocyanins, found in blueberries, blackberries and cherries, had the most protective effect. The people in the group that represented the highest 20% of flavonoid consumers, on average, had about 600 milligrams (mg) in their diets each day, compared to the people in the lowest 20% of flavonoid consumers, who had about 150 mg in their diets each day. Strawberries, for example, have about 180 mg of flavonoids per 100 gram serving, while apples have about 113. Blueberries have about 164 mg of anthocyanins per 100 gram serving. The results also showed that it’s never too late to start, because protective effects were seen whether people were consuming the flavonoids in their diet 20 years ago, or if they started incorporating them more recently.
These results are consistent with prior studies from the USA supporting higher flavonoid consumption for the prevention of Alzheimer dementia. A key part of dementia prevention strategies is also to control cardiovascular risk factors such as hypertension, high cholesterol, type 2 diabetes.
ANCIENT ANCESTORS ATE STARCHY FOODS: It is often argued by proponents of the low-carb and Paleo diet that our ancient ancestors did not eat starchy foods and this may be one reason for their better health. This new study dispels this myth. It examined the oral microbiome of Neanderthals and ancient humans and shows that humans were adapted to eating starch-rich foods as far back as 100,000 years ago, which is much earlier than previously thought.
Scientists analysed the fossilised dental plaque of both modern humans and Neanderthals and compared them to those of humanity’s closest primate relatives, chimpanzees and gorillas, as well as howler monkeys, a more distant relative. They reconstructed the oral microbiomes of Neanderthals, primates, and humans, including what’s believed to be the oldest oral microbiome ever sequenced — a 100,000-year-old Neanderthal.
The findings suggest starchy foods became important in the human diet well before the introduction of farming and even before the evolution of modern humans. And while these early humans probably didn’t realise it, the benefits of bringing the foods into their diet likely helped pave the way for the expansion of the human brain because of the glucose in starch, which is the brain’s main fuel source.
The results showed the presence of particular strains of oral bacteria that are specially adapted to breaking down starch. These strains, are members of the genus Streptococcus, have a unique ability to capture starch-digesting enzymes from human saliva, which they then use to feed themselves. The genetic machinery the bacteria uses to do this is only active when starch is part of the regular diet. Both the Neanderthals and the ancient humans that scientists studied had these starch-adapted strains in their dental plaque while most of the primates, who feast almost exclusively on non-starchy plant parts, like fruits, stems, and leaves, had almost no streptococci that could break down starch. The findings suggest that early humans did indeed consume a diet rich in starchy foods including roots and tubers and also nuts and seeds.