Good science starts with careful observation and the formation of hypotheses which are then tested. When we observe various phenomena, we often find things that tend to occur together. This is called correlation. Our temptation is to assume that things which naturally go together have a cause and effect relationship. For example, in the 50’s, epidemiologists found that many countries with a diet low in fat had very low rates of heart disease and made the natural mistake of assuming that low fat diets prevented heart disease. A large amount of evidence has now accumulated that this is wrong but not before millions were hurt. With this in mind, I’ll start this discussion of gut microbes and obesity/metabolic disease with some interesting correlations between disruption of the microbe population and disease. I previously mentioned the fact that babies delivered by c-section have altered gut bacteria. It turns out that these babies grow up to have a higher rate of obesity and diabetes. We know that antibiotics can kill healthy bacteria in the gut and now find that regions with high antibiotic use have higher rates of obesity. Finally, we are consistently finding that gut bacteria in obese individuals is much less diverse that in lean folks. This has been compared to a rain forest exposed to acid rain and other hazards having a reduced biodiversity and thus less able to sustain life . Also, we find certain species of bacteria with varied levels in obese verses lean folks. For example, obesity is associated with higher levels of Firmicutes and reduced Bacterioidities. Before you run out and buy the latest probiotic containing Bacterioidities which promises weight loss, remember that I am only mentioning correlations. Next time, I’ll cover some clever and fascinating studies which seem to confirm cause and effect between obesity/diabetes and disrupted gut flora.