Vaccines and antibiotics may someday join caloric restriction or bariatric surgery as a way to regulate weight gain, according to a new study focused on the interactions between diet, the bacteria that live in the bowel, and the immune system.
Bacteria in the intestine play a crucial role in digestion. They provide enzymes necessary for the uptake of many nutrients, synthesize certain vitamins and boost absorption of energy from food. Fifty years ago, farmers learned that by tweaking the microbial mix in their livestock with low-dose oral antibiotics, they could accelerate weight gain. More recently, scientists found that mice raised in a germ-free environment, and thus lacking gut microbes, do not put on extra weight, even on a high-fat diet.
In a study, published Aug. 26 in the journal Nature Immunology, a research team based at the University of Chicago was able to unravel some of the mechanisms that regulate this weight gain. They focused on the relationship between the immune system, gut bacteria, digestion and obesity. They showed how weight gain requires not just caloric overload but also a delicate, adjustable and transmissible interplay between intestinal microbes and the immune response.
"Diet-induced obesity depends not just on calories ingested but also on the host's microbiome," said the study's senior author Yang-Xin Fu, MD, PhD, professor of pathology at the University of Chicago Medicine. For most people, he said, "host digestion is not completely efficient, but changes in the gut flora can raise or lower digestive efficiency."
So the old adage "you are what you eat" needs to be modified, Fu suggested, to include, "as processed by the microbial community of the distal gut and as regulated by the immune system."
To measure the effects of microbes and immunity, the researchers compared normal mice with mice that have a genetic defect that renders them unable to produce lymphotoxin, a molecul
|Contact: John Easton|
University of Chicago Medical Center