A study by Stanford University School of Medicine investigators raises concerns that the lower-fiber diets typical in industrialized societies may produce internal deficiencies that get passed along to future generations.
The study, conducted in mice, indicates that low-fiber diets not only deplete the complex microbial ecosystems residing in every mammalian gut, but can cause an irreversible loss of diversity within those ecosystems in as few as three or four generations.
Once an entire population has experienced the extinction of key bacterial species, simply “eating right” may no longer be enough to restore these lost species to the guts of individuals in that population, the study suggests. Those of us who live in advanced industrial societies may already be heading down that path.
The proliferation of nearly fiber-free, processed convenience foods since the mid-20th century has resulted in average per capita fiber consumption in industrialized societies of about 15 grams per day. That’s as little as one-tenth of the intake among the world’s dwindling hunter-gatherer and rural agrarian populations, whose living conditions and dietary intake presumably most closely resemble those of our common human ancestors, said Justin Sonnenburg, PhD, associate professor of microbiology and immunology and senior author of the study, published Jan. 13 in Nature.
Virtually all health experts agree that low-fiber diets are suboptimal. Probably the chief reason for this is that fiber, which can’t be digested by human enzymes, is the main food source for the commensal bacteria that colonize our colons, Sonnenburg said.
Thousands of distinct bacterial species inhabit every healthy individual’s large intestine. “We would have difficulty living without them,” he said. “They fend off pathogens, train our immune systems and even guide the development of our tissues.” While we pick up these microscopic passengers in the course of routine exposures throughout our lifetimes, one of the most significant sources of our intestinal bacterial populations is our immediate family, especially our mothers during childbirth and infancy.
Surveys of humans’ gut-dwelling microbes have shown that the diversity of bacterial species inhabiting the intestines of individual members of hunter-gatherer and rural agrarian populations greatly exceeds that of individuals living in modern industrialized societies, Sonnenburg said. In fact, these studies indicate the complete absence, throughout industrialized populations, of numerous bacterial species that are shared among many of the hunter-gatherer and rural agrarian populations surveyed, despite those groups’ being dispersed across vast geographic expanses ranging from Africa to South America to Papua New Guinea.
High- versus low-fiber diet
“Numerous factors including widespread antibiotic use, more-frequent cesarean sections and less-frequent breastfeeding have been proposed for why we see this depletion in industrialized populations,” said the study’s lead author, Erica Sonnenburg, PhD, a senior research scientist at Stanford (she and Justin Sonnenburg are married). “We asked ourselves whether the huge difference in dietary fiber intake between traditional and modern populations could, alone, account for it.”