NEW YORK (Reuters Health) - Higher-fat diets have unfavorable effects on gut microbiota, fecal metabolites and plasma proinflammatory factors, researchers from China report.
"The higher-fat diet was associated with significant and potentially detrimental changes in long-chain fatty acid metabolism, resulting in higher levels of chemicals that are thought to trigger inflammation," Dr. Duo Li from Qingdao University told Reuters Health by email. "These effects may sow the seeds for the development of metabolic disorders and cardiovascular disease, such as diabetes, heart disease, and stroke, over the longer term."
In China, the recent transition from the traditional low-fat, high-carbohydrate diet to one higher in fat and lower in carbohydrate has been associated with a dramatic increase in the risk of obesity, type 2 diabetes, and cardiovascular diseases.
Previous research has linked high-fat diets with reductions in human gut microbiota diversity and richness, changes that have been postulated as a major trigger of metabolic impairments associated with obesity.
Dr. Li's team compared gut microbiota and fecal metabolomic profiles as well as markers of inflammation in 217 healthy adults who had been randomized to one of three diets for six months: a lower-fat diet (20% fat, 66% carbohydrate), a moderate-fat diet (30% fat, 56% carbohydrate), or a higher-fat diet (40% fat, 46% carbohydrate).
All three groups lost weight during the intervention, and the weight reduction was significantly greater in the lower-fat group than in the higher-fat group, as were reductions in waist circumference, total cholesterol, HDL-cholesterol, LDL-cholesterol and non-HDL-cholesterol.
The lower-fat diet was associated with significantly increased microbial community diversity relative to the higher-fat diet. The higher-fat diet decreased the abundance of Faecalibacterium and increased the abundance of Alistipes and Bacteroides, whereas the lower-fat diet increased the abundance of Faecalibacterium and Blautia.
The higher-fat diet was associated with significant decreases in the concentration of short-chain fatty acids, compared with the other diets, while the lower-fat diet was associated with decreases in two cometabolites (p-cresol and indole) that have been linked to host metabolic disorders.
Plasma concentrations of several inflammatory markers were increased during the higher-fat diet and decreased during the lower-fat diet, the team reports in Gut, online February 19, 2019.
"These findings provide confirmatory evidence that nutritional guidelines in countries in a state of nutrition transition should advise against increasing intakes of dietary fat," the researchers conclude. "The results might also have relevance in developed countries in which fat intake is already high."
"We suggest that fat intake for the general healthy population should not be more than 30% of total energy," Dr. Li said. "We also suggest that the general healthy population should use polyunsaturated or monounsaturated plant fat, such as soybean oil, rape seed oil, peanut oil, olive oil, etc. for cooking."
Dr. Stefano Menini from Sapienza University of Rome, who recently sought to differentiate metabolically healthy from metabolically unhealthy obesity, told Reuters Health by email, "These findings indicate that increasing the dietary content of fat induces microbiome changes similar to that observed in human obesity and type 2 diabetes, even without increasing calorie intake and body weight. A Western-style diet, that is typically enriched in fats and deprived of fibers, may alter the gut microbiota structure and activity regardless of its obesogenic action, with ensuing adverse effects on intestinal permeability, systemic inflammation, and metabolism dysregulation."
"These findings might even be undervalued relative to real-world conditions," explained Dr. Menini, who was not involved in the work. "In this study, soybean oil was added to reach the desired amount of dietary fat. Whether saturated fats of animal origin led to the same changes in gut microbiota and fecal metabolites needs to be studied further. It could be that the type of fat, in addition to the quantity, can influence the composition and activity of the gut microbiota, and that a Western-style diet, which is particularly rich in saturated fats, can induce even more unfavorable alterations than those induced by a diet reach in soybean oil."
Dr. Debby P. Y. Koonen of University Medical Center Groningen, in the Netherlands, who studies various aspects of the gut microbiota and was not involved in the new work, told Reuters Health by email, "Of particular interest are the results on the short-chain fatty acids (SCFAs) in the study. They are in line with the increasing number of publications that highlight a protective role of SCFAs in numerous diseases."