"Here's a crazy one you might not have heard: did you know that if you have the wrong type of gut bacteria, those bacteria can cause weight gain? In studies done with morbidly obese people, it was observed that certain strains of bacteria more efficiently extracted calories and nutrition out of food than others. , It just depends on what combination of gut flora you have — that same handful of crackers you eat may or may not have the same caloric impact on the next person. And how do we have such wildly differing gut bacteria? Well, the average child, by the time they start school, has had 20 different antibiotic prescriptions. How many have you had over your lifetime?"
Why You Are Fat: What You Can Do About It