What is already known
About 30% of the world’s population suffers from nonalcoholic fatty liver disease (NAFLD) — a condition in which excess fat builds up in the liver. There is currently no approved medicine available for NAFLD. However, previous studies have linked NAFLD to alterations in gut bacteria: for example, at the onset of the disease, people with NAFLD already show an altered gut microbiota.
What this research adds
Researchers conducted a clinical trial in 200 people with NAFLD. Half of the participants received a dietary supplement containing resistant starch, a type of carbohydrates that pass through most of the digestive system unchanged. The other half of the participants received a type of non-resistant starch as a control. After 4 months, participants who consumed resistant starch showed a reduction of about 40% in the levels of fatty molecules in their livers as well as proteins associated with liver injury and inflammation. Transferring gut microbes from people who consumed resistant starch to mice fed with a high-fat diet resulted in a reduction in the buildup of fat in the liver.
Conclusions
The findings suggest that resistant-starch supplements can alter the gut microbiota in ways that alleviate NAFLD.
About 30% of the world’s population suffers from nonalcoholic fatty liver disease (NAFLD) — a condition in which excess fat builds up in the liver. Now, findings from a clinical trial show that when consumed by people with NAFLD, specific carbohydrates found in legumes and other foods can alter gut bacteria composition in ways that reduce the levels of proteins associated with liver injury and inflammation.
The findings, published in Cell Metabolism, may inform the treatment of NAFLD, for which there is no approved medicine available.
“We think it would be very meaningful if we can find an effective approach, maybe through identifying new therapeutic targets, to manage NAFLD,” says study co-author Huating Li at Shanghai Sixth People’s Hospital in China.
Previous studies have linked NAFLD to alterations in gut bacteria. For example, at the onset of the disease, people with NAFLD already show an altered gut microbiota. To find potential approaches to treat NAFLD, Li and her colleagues set out to investigate the effects of resistant starch, a type of carbohydrates that pass through most of the digestive system unchanged. These carbohydrates, which are found in foods including bread, pasta and legumes, are known to boost the growth of beneficial gut bacteria.
Starch supplement
The researchers conducted a clinical trial in 200 people with NAFLD. At the beginning of the trial, all participants received a balanced dietary plan designed by a nutritionist. Half of the participants also received a resistant starch supplement derived from maize, while the other half received a type of non-resistant starch as a control. Each participant had to take the starch supplement before meals twice a day for 4 months.
After 4 months, participants who consumed resistant starch showed a reduction of about 40% in the levels of fatty molecules called triglycerides in their livers compared with controls. High triglycerides are known to lead to fatty liver disease. Participants on the resistant-starch supplement also showed reductions in the levels of proteins associated with liver injury and inflammation.
These benefits on the liver were independent of body weight changes, the researchers found.
Alleviating disease
Compared with controls, people who consumed the resistant-starch supplement had a different microbiota composition. In particular, they had lower levels of Bacteroides stercoris, a bacterial species that can influence fat metabolism in the liver. Indeed, the reduction in B. stercoris was associated with a decrease in liver triglyceride levels, the researchers found.
Transferring gut microbes from people who consumed resistant starch to mice fed with a high-fat diet resulted in a reduction in liver triglyceride content. Mice that received gut bacteria from people on the resistant-starch supplement also showed a decreased buildup of fat in the liver compared with mice that received gut microbes from controls.
“We are able to identify a new intervention for NAFLD, and the approach is effective, affordable and sustainable,” Li says. “Compared with strenuous exercise or weight loss treatment, adding resistant starch to a normal and balanced diet is much easier for people to follow through.”
