Mostly based on studies like THIS (abstract only), there's a new whiff in the air around obesity researchers. Some go so far as to call gut microflora an "unsung organ". Some have picked up this ball and run with it to the point of making wild claims that microflora control how much energy we extract from our food and we have no control over "energy in".
Our results indicate that the obese microbiome has an increased capacity to harvest energy from the diet.Firstly, we have correlation here, not causation.
Furthermore, this trait is transmissible: colonization of germ-free mice with an 'obese microbiota' results in a significantly greater increase in total body fat than colonization with a 'lean microbiota'.
Many have read this and jumped all over it to say this indicates the arrow of causation goes from microflora to obesity. That seems reasonable until one considers what actually happened here. Germ-free mice are smaller because they lack a major component in extraction of energy from their diet. I discussed this in Of Mice, Men & Microflora I. Basically, rodents are hindgut fermenters who rely on fermentation for a significant amount of energy extracted from food. Their digestive systems are clearly different from the human digestive system. If you colonize their guts with more bacteria that are efficient energy extractors, is it any surprise the animal gains more weight? But this does not indicate causality because we do not know the microflora composition of the obese mice before they became obese. My gut { pun alert } reaction on all this is that a nutrient dense intestine favors the growth of certain bacteria over others, and the direction of causality goes from hypercaloric diet to microflora + obesity.
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