Different kinds of bacteria that live inside the gut can help spur obesity or protect against it, say scientists at Washington University in St. Louis who transplanted intestinal germs from fat or lean people into mice and watched the rodents change.
When rats were given lactic acid bacteria while in utero through adulthood, they put on significantly less weight than other rats eating the same high-calorie diet. They also had lower levels of minor inflammation, which has been associated with obesity.
Similarly, in human babies gut bacteria have also been shown to impact weight. One study found babies with high numbers of bifidobacteria and low numbers of Staphylococcus aureus — which may cause low-grade inflammation in your body, contributing to obesity — appeared to be protected from excess weight gain. This may be one reason why breast-fed babies have a lower risk of obesity, as bifidobacteria flourish in the guts of breast-fed babies.
This is only the beginning of research showing that lean people tend to have higher amounts of various healthy bacteria compared to obese people.
In 2006, Stanford University researchers found that obese people had different gut bacteria than normal-weighted people — a first indication that gut flora plays a role in overall weight.
We all develop with an essentially sterile digestive tract. Bacteria rapidly move in starting at birth – bugs that we pick up from mom and dad, the environment, first foods. Ultimately, the intestine teems with hundreds of species, populations that differ in people with varying health. Overweight people harbor different types and amounts of gut bacteria than lean people, for example. The gut bacteria we pick up as children can stick with us for decades, although their makeup changes when people lose weight, previous studies have shown. Clearly, what you eat and how much you move are key to how much you weigh.