Prebiotics for Frailty

Prebiotics for Frailty

The anti-inflammatory effects alone could explain why people who eat more fiber tend to live longer and healthier. A systematic review with meta-analysis of data from more than 100 million person-years found that people who consumed the most fiber had a 15 to 30 percent lower risk of overall mortality than those who consumed the least fiber, including the risks of being struck by heart disease, stroke, or cancer and dying from them. Fiber intake is also associated with a significantly higher likelihood of “successful aging,” defined as the absence of disability, cognitive impairment, depression, respiratory complaints, and chronic disease.

Prebiotics and postbiotics have been shown to extend the lives of model animals, but intervention studies in humans are largely limited to risk factors. For example, a meta-analysis of more than 50 randomized controlled trials showed: prebiotics such as fiber can regulate blood sugar, blood pressure, weight, and cholesterol significantly better. In see.nf/frailtyprebiotics I point out that a randomized, controlled, double-blind study investigating the effect of prebiotics on frailty showed significant improvements in exhaustion and muscle strength.

When we eat high-fiber foods, we get a double benefit: short-chain fatty acids are formed, and the bacteria that produce these fatty acids are selectively cultivated. The colon contents of people who eat more plants can form almost three times as many short-chain fatty acids, gram for gram. When we eat healthfully, we not only get more raw material for SCFA production, but also a more powerful microbial setup that produces even more of them. In contrast, a low-carbohydrate diet can throttle short-chain fatty acid production by up to 75 percent.

Promoting Prevotella

In the chapter “Microbiome-Friendly” in my book How Not to Diet, I describe that humanity essentially splits into two enterotypes: people who eat more healthfully and primarily promote Prevotella bacteria, and those who eat a Western diet and primarily bring forth Bacteroidetes. If that sounds strange to you—thousands of bacterial species, but only two gut types—then imagine the gut as an ecosystem. On our planet there are several million animal species, but they are not randomly distributed. Jungle animals live in the jungle and desert animals in the desert. Each ecosystem exerts specific selection pressure through its conditions, such as temperature, humidity, and amount of rainfall. Apparently, there are two kinds of ecosystems in the colon, by which we can be divided into groups: in the guts of one group, mainly bacteria of the Prevotella type grow, and in those of the other group, Bacteroidetes species.

Since Prevotella are fiber-eaters, they produce more short-chain fatty acids, which may explain why African Americans (who typically have a Bacteroidetes enterotype) develop colon cancer 50 times more often than Africans (who typically harbor Prevotella). But you can switch your gut flora from one type to the other within a few days; to do that, you only need to switch between plant-based and animal-based diets.

In addition, Prevotella have anti-inflammatory effects, which is why a lower abundance of these bacteria is also observed in autoimmune diseases such as Hashimoto’s thyroiditis, multiple sclerosis, and type 1 diabetes. Presumably for that reason as well, autoimmune diseases were rare or nearly unknown among people in rural regions of sub-Saharan Africa who ate an almost exclusively plant-based diet. Most studies report that vegetarians have higher Prevotella counts, but when researchers switched them to meat, eggs, and dairy products, their Prevotella levels plummeted within four days.

For a beneficial microbiome that lets you age healthfully, a predominantly plant-based diet is recommended. Vegetarians tend to harbor more potentially probiotic (good) bacteria, while omnivores brim with potential pathobionts (bad bacteria). Intake of plant protein is associated with a greater prevalence of bifidobacteria and Lactobacillus, higher production of short-chain fatty acids, less inflammation, and an improved gut barrier, whereas consuming animal protein promotes the growth of bacteria such as Bilophila and leads to a decline in short-chain fatty acid production and an increase in toxic metabolic products such as TMAO.

A comparison of stool samples from vegans, vegetarians, and omnivores found a continuum of inflammatory markers, with a clear rise the lower the plant-based share of the diet became—inflammation that can be stopped by switching to a purely plant-based diet. This is probably more due to the protective effects of plants than to the harmful effects of animal products. A thorough study of the microbiome and eating habits of more than 1000 people found that the dietary factor that most strongly shapes the gut flora is the amount and variety of healthy plant foods. The microbiomes of people who consumed fiber-stripped industrial foods such as soft drinks and refined-grain products lined up with those of people who ate predominantly animal-based diets. So junk-food vegans aren’t doing their good bacilli much of a favor.

It doesn’t have to be black and white, all or nothing. People who ate a Mediterranean diet, with lots of beans, fruits, and vegetables, and didn’t eat meat (or fish), eggs, and dairy products every day, had similar amounts of short-chain fatty acids as vegans, even though they did not eat an exclusively plant-based diet.

Fiber Is the Be-All and End-All

The benefit of short-chain fatty acids depends on whether we eat fiber and have fiber-eating microbes, just as for the harmful effects of TMAO we not only have to eat eggs, dairy, or meat, but also have to carry within us the bacteria that themselves eat eggs, dairy, and meat. Remember the steak-eating vegan? He had no TMAO-generating harmful bacilli in his gut, and it could take months of steak eating to ramp up their production. Correspondingly, for people who eat less healthfully, it can take several months to fully tap the potential of increased fiber intake, since their microbiome first has to build up from fiber-eating organisms.

In see.nf/cultivate I describe in detail that the benefit of higher fiber intake levels off once the available stock of fiber-eaters is saturated, but for people who have habitually cultivated the growth of fiber-eaters like Prevotella, there is no limit. In the United States, the recommendation for daily fiber intake is at least 14 grams per 1000 calories, which means about 25 grams for women and 38 grams for men. And although that is still far from the 100 grams our body is built for (based on the diets of hunter-gatherer tribes still living in isolation today, as well as analysis of coprolites, fossilized human feces), not even 3 percent of Americans reach the minimum recommended minimum.

We know that fiber, plant fiber, logically occurs only in plants—hardly at all in industrial foods and not at all in animal foods. Since fruits and vegetables consist largely of water, the fiber superstars of the plant kingdom are the grains and legumes. A cup of fruit may contain only 3 grams of fiber and a cup of vegetables 5 grams, but a cup of beans or a cup of grains such as barley groats can contain 15 grams of fiber.