Remember how obese people and mice have more Firmicutes and fewer Bacteroidetes than their lean counterparts? This result, the F/B ratio, is one of the most famous in the field – and it’s a mirage. In 2014, two attempts to re-analyse past studies found that the F/B ratio is not consistently connected to obesity in humans.53 You can tell the difference between obese and lean microbiomes within any single study, but there are no consistent differences across studies. This doesn’t refute a connection between the microbiome and obesity. You can still fatten germ-free mice by loading them with
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