New research uses a "human gut simulator" to study the effects of two different diets on the composition of gut microbiota. Its findings illuminate the harms of having no carbs in the diet.
Recently, there has been a lot of debate over the role of carbohydrates in one's diet.
On one hand, a diet low in carbs has been shown to stave off insulin resistance and metabolic syndrome.
Low-carb, high-fat diets such as the keto diet — which more and more people are adopting to lose weight — have been suggested to have several benefits.
These range from improving cardiovascular health to keeping the brain healthy.
On the other hand, recent studies have suggested that too few carbs in our diet may raise mortality risk, while other researchers have downright discouraged people from adopting low-carb diets, deeming them "unsafe."
Most studies in the latter category are observational studies, but new research helps elucidate the effects of a diet low in carbs and high in fat on gut microbiota by using an artificial intestine.
Scientists led by Richard Agans, of the Department of Biochemistry and Molecular Biology at the Wright State University in Dayton, OH, conducted the new study.
Its findings were recently published in the journal Applied and Environmental Microbiology.
The health benefits of eating carbs
Agans and colleagues designed an artificial intestine, or human gut simulator, whose main purpose was to simulate the environment found inside the human colon.
The researchers used fecal samples from donors to recreate this bacterial environment and added nutrients first from a balanced Western diet, and then from a no-carb, no-protein diet made exclusively of fats.
Then, they applied a range of cutting-edge technologies to examine and measure the composition of metabolites resulting from changing the nutrients.
The study revealed that switching from a balanced diet to a high-fat, no-carb diet increased strains of bacteria that metabolize fatty acids. The switch also lowered bacteria such as Bacteroides, Clostridium, and Roseburia, which are responsible for degrading proteins and carbs.
In turn, this reduced the production of short-chain fatty acids and antioxidants, which are chemical compounds that fight DNA damage and aging by countering the harmful effects of free radicals.
When gut bacteria metabolize carbs, say the researchers, they release short-chain fatty acids, which have positive health effects such as reducing inflammation and colon cancer risk.
"The relative beneficial and harmful effects of the high-carb and high-fat diets are a subject of many studies and debates," says corresponding study author Dr. Oleg Paliy, an associate professor at Wright State University's Boonshoft School of Medicine.
However, "One aspect rarely considered in the above debate," point out the study authors, "is how macronutrient composition of a diet impacts the environment of the colon and the gut microbiota residing in that region."
"Intestinal microbes mediate many dietary effects on human health," adds Dr. Paliy. "There, most of these compounds are fermented by gut bacteria."
"This happens," he notes, "because a significant proportion of dietary carbohydrates, proteins, and fats escapes digestion in the small intestine, and reaches the colon, a section of the gut housing a dense population of microbes."
The new study "showed that human gut microbiota can utilize dietary fatty acids to sustain growth."
Changing to a fat-only diet, the authors explain, "led to a substantial decrease in the production of [short-chain fatty acids] and antioxidants in the colonic region of the gut, which might potentially have negative health consequences on the host."