If you're in a hurry, it's the sort of study you could easily overlook. I know I almost did. In late August, the journal Nature released research online that linked eating a low-fat diet to improving the quality of bacteria in your gut.

So what?So this study was just one of the three recently released to suggest that the type and amount of microbacteria inside your gut determines to some degree how readily you gain weight. In fact, one study with mice given bad human gut bacteria found the type of human bacteria given to the mice affected the rate at which they burned calories especially when combined with a bad diet.In other words, the quality and amount of gut bacteria may very well be one of the reasons why you gain weight even when you're watching what you eat. And if that's the case, gut bacteria or lack or quality of it could also be a cause of the obesity epidemic that's not only adversely affecting health but also shortening life span.But you don't need to reach the point at which most doctors deem you to be obese generally seen as more than 20 percent over your suggested weight to lessen your life span. Statistics complied over 38 years on nearly 46,000 men from Sweden determined that just being slightly overweight will do that.The study published in what used to be called the British Medical Journal used body mass index to determine whether the subjects whose average age was just under 19 at the start of the study were considered normal weight (18.5 to 24.9 on the BMI), overweight (25.0 to 29.9), or obese (over 30).The researchers factored out such variables as economic status, strength, and cigarette smoking. The data revealed that those who were obese at the study's start were 114 percent more likely to die than those of normal weight.And those men considered overweight sometimes by just a few pounds were 33 percent more likely to die during the study than those of normal weight.It's percentages like these that make a study published in the journal Nature so significant. Researchers looked at the gut bacteria of nearly 200 Danish men and women and discovered about 25 percent of them were lacking about 40 percent of the bacteria genes that people generally possess.That 25 percent were more likely to have gained weight in the last nine years and were also more likely to be obese. Some critical health indicators were also problematic, too.The 25 percent also had an increase in the markers that lead to insulin resistance, increasing the likelihood of diabetes, as well as an increase in the type of inflammation that often leads to heart disease.Other research performed at Washington University's School of Medicine and published in the September issue of Science made the correlation between gut bacteria and weight gain even more apparent.In this study, gut bacteria was taken from human beings and given to mice that were bred and raised in such a way that they had no gut bacteria of their own. All the human samples came from twins, one of whom was lean and one of whom was fat.All mice ate a standard diet, but the mice given the gut bacteria from the fat twins gained more weight than the mice given gut bacteria from the lean twin. That's because the "fat" gut bacteria actually altered their metabolisms.Up to this point in the study, the mice given the "lean" gut bacteria were kept separate from the the ones given the "fat" gut bacteria. When they were allowed to commingle for 10 days, something odd occurred: the mice who had received the gut bacteria from the fat twins lost some weight and experienced another change in their metabolisms.How did this happen?Mice eat feces.The mice given the gut bacteria from the fat twins were now eating the feces of the mice given the gut bacteria of the lean twins, and the good gut bacteria in it was undoing the damage done by the bad gut bacteria.Fortunately, the reverse did not occur. The lean mice eating the feces of the fat mice did not gain weight or experience a change in metabolism. For some reason, the bad gut bacteria did not take hold once the good gut bacteria had established a stronghold.In the final element to this research, however, the researchers formulated a mix of food for the mice that represented the typical American diet one low in fiber and high in saturated fat. Now the lean mice who had been unaffected by eating the feces of the fat mice gained weight. Now the bad gut bacteria overtook the good.As has been written in this column on many occasions in the past, nutritional science is still in its infancy. It's humbling how much we don't understand about how the body handles food.One thing is becoming more and more apparent as research continues, though. While the body may be tremendously resilient, it still gets adversely affected by processing unhealthy food.These three studies show just how far ranging the damage done by eating the typical American diet can be.