Can the right gut bacteria make you thin?

photo: Pacific Northwest National Laboratory via Flickr

photo: Pacific Northwest National Laboratory via Flickr

Recently, the main stream media was buzzing with the news that gut bacteria can make people thin.  Or at least they jumped to that conclusion, based on a study with this title:

“Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice”

What the heck does that even mean?  First off, it means the study was done on mice, not on humans.  So leaping to the conclusion that taking a pill with the “right” bacteria will cure obesity is not even remotely justified.

The study was rather complicated, and did involve at least a few actual humans.  They were 4 pairs of twins, eight people.  These particular twin pairs were “discordant” for obesity, meaning one twin was lean and one obese, despite being twins.  The researchers figured that meant the twins might have different bacteria populations.  They took samples from eat set of twins, and “transplanted” (don’t ask) these samples to mice.  The mice were fed different types of diets

  1. Low fat, plant based mouse chow
  2. A high saturated fat diet, low in fruits and vegetables
  3. A low saturated fat diet rich in fruits and vegetables.

What were the results?

  • The mice with the obese twins’ bacteria gained more fat tissue.
  • When lean and obese-bacteria mice were put in the same cages and fed the low fat-high fruit/vegetables diet, the obese mice reverted to a bacteria profile like the lean mice.
  • BUT when lean and obese mice in the same cage were fed the high saturated fat diet, the obese-bacteria mice were not protected from gaining weight.

What does this mean in the real world?

* Mice with bacteria from an obese person gained fat weight more easily.  This suggests that there’s something about gut bacteria that contributes to obesity.  What it doesn’t suggest is which bacteria are obesity-related, and which bacteria would reverse the effect.  It’s far too early for anyone to make recommendations about specific probiotics for weight loss.

* A low fat, plant based diet caused obese-bacteria mice to revert to a lean-bacteria profile.  Plenty of research links that type of diet to lower risk for obesity and chronic disease in humans, although the exact mechanism isn’t known.  A low fat plant based diet can encourage a different gut bacteria population compared to a high fat, low fiber diet.

Or, as one researcher noted, any effective probiotic therapies for obesity will depend on the dieter adopting a diet that encourages those bacteria to thrive: a low fat, largely plant-based diet.  Simply taking a probiotic weight loss pill while eating the same old high fat, processed, low plant food diet won’t work.  Another recent study from Denmark supports this idea.  In that study, but bacteria populations from obese and non-obese people were compared.  The lean people has a rich diversity of gut bacteria.  People with a less rich population of bacteria were more likely to be fat, have metabolic syndrome and gain weight easily.

Bottom line: if you want to lose weight and keep the weight off, the best change you can make is to permanently switch to a low fat plant-based diet.

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