Three recent studies look at gut microbiota, the Mediterranean diet and nuts and their effects on health and lifespan

Put your gut microbes on a diet and live longer
The types of microbes residing in our gut can have positive or negative effects on our health and lifespan depending on their type. A Nature Communications study showed that the specific types of gut microbes residing in mice change with age and diet; as mice age, some bacterial types are evicted and replaced by other types. This microbial shift is a normal part of the aging process but can be manipulated by diet. If this mouse study holds true for humans, we may be able to change our diet and take better control of our health and lifespan.
In a 4-year study, Liping Zhao and Chenhong Zhang and their research group at the Shanghai Jiao Tong University put mice on a reduced calorie, low-fat diet for their entire lives. When the researchers sampled the mouse gut microbes at several life stages, the reduced-calorie, low-fat-dieting mice contained more beneficial Lactobacillus, which inhibit pathogens sticking to the wall of the intestine, than mice on other diets. Inflammation-inducing bacteria, such as Streptococcaceae, were reduced in this group. The lean-mean group also had the lowest blood glucose and lipid levels, which, when high, contribute respectively to diabetes and arterial disease. If you haven't put your ice cream spoon down yet, the weight-watcher mus musculus weighed less, their body weights were more stable, and they lived 20-25% longer than other mice in the study.

Besides these positive effects, as the reduced-calorie, low-fat-dieters aged, the number and type of beneficial gut bacteria were found to increase throughout their lifespan, which was longer compared with other groups. The converse was also true; the harmful microbes and those negatively correlated with increased lifespan decreased. The Zhao-Zhang study illustrates how diet can modify gut microbes and affect lifespan in mice but it also suggests that improvement of gut bacteria may provide a new standard for testing dietary drugs aimed at increasing lifespan in humans.

Two recent nutritional studies recommend the consumption of nuts, especially walnuts, in order to reduce cardiovascular problems such as stroke, heart attack, or death from cardiovascular causes. A New England Journal of Medicine study conducted in Spain on subjects at high cardiovascular risk examined the effect of the Mediterranean diet supplemented with either olive oil or nuts. The Mediterranean diet consists of large amounts of olive oil, fruits, nuts, vegetables and cereals, reduced dairy products, red meat, processed meats and sweets, a moderate intake of fish and poultry, with wine accompanying meals.

The NEJM study was run by the PREDIMED doctors, including Ramon Estruch and Miguel Angel Martinez-Gonzalez. They enrolled over 7000 older (aged 55-90) men and women suffering from either diabetes or at least three other risk factors, smoking, hypertension, elevated LDL-cholesterol levels, low HDL-cholesterol levels, overweight or obesity, or a family history of premature coronary heart disease. The study subjects were randomly assigned to a Mediterranean diet supplemented with olive oil, a Mediterranean diet supplemented with nuts, or a control low-fat diet. Both types of supplementation reduced the risk of major cardiovascular events.

Sabine Rohrmann and David Fach from the Institute of Social and Preventive Medicine at the University of Zurich report a study by Marta Guasch-Ferre of the Universitat Rovira i Virgili published in BMC Medicine that used the PREDIMED nutrition study data to analyze the positive effects of nut consumption on lifespan and health. They found that people eating three or more servings of walnuts and other types of nuts a week were less likely to die of cancer or cardiovascular diseases and to live longer than nut abstainers.

Put the nut back in nutrition
Nutritional studies have shown the positive effects of eating nuts on blood vessel elasticity. Increasing blood vessel elasticity through dietary management reduces cardiovascular disease. Professor Guasch-Ferre speculates that the reason walnuts may have a more beneficial health effect than other nuts is their high content of the unsaturated fat alpha-linolenic acid, an essential fatty acid that cannot be made by the body. Chemicals, called phytochemicals, which are made in plants and protect against diseases, are also easier to absorb in walnuts than other nuts. Further studies will be done to understand the amount of walnuts an individual would need to consume to reduce his/her risk of cancer, cardiovascular or other diseases. Dietary guidelines already recommend replacing one of the five recommended servings of fruits or vegetables a day with a serving of nuts.