Cultivate the thinner inner-you

Research indicates that you can lose weight by cultivating greater diversity of bacteria in your gut says Claudia Wells in Scientific American.

“New evidence indicates that gut bacteria alter the way we store fat, how we balance levels of glucose in the blood, and how we respond to hormones that make us feel hungry or full. The wrong mix of microbes, it seems, can help set the stage for obesity and diabetes from the moment of birth,” explains Wells.


Studies of identical human twins, one obese and the other lean, reveal that the gut bacteria of lean twins is more diverse. These Bacteroidetes specialize in breaking down bulky plant starches and fibres into shorter molecules that we can use as energy.

Studies in mice back this up. First, genetically identical mice were raised in a germ-free environment and separated into two cages. Then one group was populated with gut bacteria from an obese human twin and the other half with gut bacteria from the lean twin. Both groups were fed exactly the same. The mice with gut bacteria from the obese human twin became fatter while their siblings with lean human bacteria did not.

Then researchers, whose findings were published in the journal Science last September, moved the two groups into the same cage. The fat mice became thin because, unappealing as it may seem, mice consume each other’s feces.

Why didn’t the lean mice become fat rather than the other way around? In a word: diversity.

The researchers theorize that a diverse population of gut bacteria perform specific functions. One is to help regulate hunger so that lean people will feel full after eating. Another eliminates certain amino acids that are elevated in obese people and lead to type 2 diabetes.

While a diverse gut populations contribute to thinness, food still matters.  When mice who had become lean were fed a typical “Western diet,” they grew fat. Their siblings who were fed a diet low in fat and high in fruit, vegetables and fibre remained thin.

Growing a diverse garden of gut bacteria takes care. It starts on the day we are born when mothers give newborns a “bacterial baptism” through vaginal birth. Breast milk nurtures useful bacteria and inhibits harmful ones.

Antibiotics kill not just the weeds in this biological garden but also valuable species. “Antibiotics are like a fire in the forest,” says one researcher. They wipe out entire swathes of microbes and leave fewer to populate the gut.

Diets that are high in fat and antibiotics cause weight gain in mice and that appears to be true in humans. For ethical reasons, the design of human experiments proving the connection would be difficult.  However, circumstantial evidence exists. Maps showing obesity in the Southern U.S. line up with maps of high fat diet and high antibiotic use.

The research requires a re-thinking of who “we” are since the microbes that live in our intestines, mouth, nose, skin and genital tract outnumber “us” by a factor of ten. More realistically, what we euphemistically refer to ourselves is simply baggage that carries our vital microbial community.