Dietary fat hurts microbiota and induces inflammation

A recent study by ZJU scientists showed higher-fat consumption might confer adverse consequences for long-term health outcomes to healthy young adults whose diet is in a state of nutrition transition.

In recent years, the notion that “it is more healthful to take in fat than to eat staple food” has gone viral in certain circles. Put it differently, people have been encouraged to eat fat-rich and low-carbohydrate food. Then is the carbohydrate food, represented by rice, the real culprit behind metabolic diseases among Chinese people?

The research team led by Prof. LI Duo with the College of Biosystems Engineering and Food Science carried out a 6-month random controlled-feeding trial. They discovered that the high-fat and low-carbohydrate diet produces an adverse impact on the gut microbiota and faecal metabolomics profiles as well as the plasma proinflammatory factors, thereby providing evidence regarding the potential hazard of the high-fat diet and offering guidance for the formulation of the dietary manual in developing and developed countries. The relevant findings are published in the journal of Gut.

The trial involved screening 1145 potentially eligible adults in two centers from January 2015 and a total of 307 healthy adults participated in a 6-month controlled feeding intervention scheme. 

At Zhejiang University, more than 1,000 volunteers signed up for this experiment. Because subjects had to punch in for dinner every day even during the summer vacation, a total of 154 volunteers engaged in this trial. At breakfast, the subjects ate cookies or bread while for lunch and supper, they had the classic “studyholic” packed food containing two meat dishes, one vegetable dish and rice. In the experiment, they also needed to have a physical checkup on a monthly basis.

cronutrients refer to the three basic components of every diet—carbohydrates, fat, and protein. In this trial, the subjects were divided into three sub-groups. All the foods were provided during the intervention period. The three isocaloric diets were: a lower-fat diet (fat 20% and carbohydrate 66% energy), a moderate-fat diet (fat 30% and carbohydrate 56% energy) and a higher-fat diet (fat 40% and carbohydrate 46% energy). Protein provided 14% energy in all three diets. The effects of the dietary interventions on the gut microbiota, faecal metabolomics and plasma inflammatory factors were investigated.

Heatmap of the median fold changes in faecal metabolite concentrations before and after the intervention

Researchers found out that the lower-fat diet was associated with increased α-diversity assessed by the Shannon index (p=0.03), increased abundance of Blautia (p=0.007) and Faecalibacterium (p=0.04), whereas the higher-fat diet was associated with increased Alistipes (p=0.04), Bacteroides (p<0.001) and decreased Faecalibacterium (p=0.04). The concentration of total short-chain fatty acids was significantly decreased in the higher-fat diet group in comparison with the other groups (p<0.001). The cometabolites p-cresol and indole, known to be associated with host metabolic disorders, were decreased in the lower-fat diet group. In addition, the higher-fat diet was associated with faecal enrichment in arachidonic acid and the lipopolysaccharide biosynthesis pathway as well as elevated plasma proinflammatory factors after the intervention.

Correlation between changes in faecal metabolites and changes in genus abundance

Compared with a lower-fat diet, long-term consumption of a higher-fat diet appears to be undesirable owing to changes in gut microbiota, faecal metabolomic profiles and proinflammatory factors for healthy young adults whose diet is in transition from the traditionally consumed lower-fat, higher-carbohydrate diet to one characterized by an appreciably higher fat content.