If a lactating mother consumes a diet lacking dietary fiber, her young offspring will lack microbial diversity in their gut and have low-grade inflammation, making them highly prone to developing obesity, according to a new study in mice. 

The findings published in the journal Cell Host & Microbe could help explain why obesity is increasing, especially in children. However, because the experiment was conducted in mice, the researchers can only speculate how much the results translate to humans. 

“As long as young mice were maintained on a standard diet, there was no difference in their weight or other metabolic parameters, regardless of whether or not their mother ate fiber,” said the senior author of the study. “But striking differences occurred when they were exposed to a Western style diet. The mice from the fiber-deprived mothers gained striking amounts of weight. The mice from the mothers who had the fiber diet gained only small amounts of weight on this diet.”

A Western style diet, also known as a fast food diet or obesogenic diet, is high in fat and low in fiber. The standard diet that young mice are raised on is a relatively healthy, mostly plant-based diet with a small amount of animal products. 

If these results translate to humans, it could help explain cases in which adolescents have very easy access to fast food diets, but some exhibit large increases in adiposity while others remain fit and lean. 

The study also found that if mothers were not consuming fiber, then the offspring didn’t get particular bacteria. If offspring don’t have those bacteria, or unless the bacteria are deliberately administered, the fiber by itself doesn’t provide a health benefit. The fiber is only beneficial if bacteria are there to metabolize it, the author explained.

The researchers studied the fecal matter of the offspring to determine the bacteria they were missing. 

“They’re missing beneficial bacteria that help keep out inflammatory bacteria,” said the lead author of the study. “The beneficial bacteria do two particular things. They can metabolize the fibers to produce beneficial products such as short-chain fatty acids and exclude bacteria that are pro-inflammatory.” 

One limitation of the study was the way the experiments were performed. The mice were kept in cages in a research facility, so they didn’t have other ways of acquiring these beneficial bacteria, unless they were deliberately administered to them. This differs from human experience. Even if a child’s mother didn’t eat fiber, that child might be able to play with other children at daycare and acquire these bacteria. 

“That’s one reason that our findings might not apply to humans, but we just don’t know,” the author said. 

Next, the researchers want to understand the mechanism behind why some mice are so prone to gain weight when exposed to obesogenic diets and then develop simple approaches to prevent passing along an unhealthy microbiome. For instance, perhaps a pregnant woman could be given dietary supplements of fiber, probiotics or a combination of the two.

https://www.cell.com/cell-host-microbe/fulltext/S1931-3128(22)00527-3