For gut bacteria, it’s the calories

There’s a certain gross out factor to a very cool new study: subjects’ poop was analyzed.  Researchers were investigating the relationship between gut bacteria, obesity and calorie intake.  Many different types of bacteria populate our intestines.  The varieties living inside you depend somewhat on your genetics, and somewhat on your diet.  They are also affected by disease states, and when you take anti-biotics, you change your bacteria population, at least temporarily.  This new study looked at the possibility that your calorie intake can affect gut bacteria.

A previous study found that, when obese people ate fewer calories and lost weight, their gut bacteria population changed to resemble that of thin people.  The researchers decided to look at what happens to intestinal microbes when people are fed excess calories.
Twelve lean and 9 obese subjects were fed two different daily calorie-levels: 2400 and 3400.  Their feces was analyzed for types of bacteria and calories, meaning available calories that hadn’t been absorbed during digestion, and were being excreted (wasted).

The results showed that, when lean people ate the high calorie diet, their bacteria population changed quickly and significantly, leading to more efficient calorie absorption.  In other words, not only were they eating more calories, but they were absorbing a higher proportion of those excess calories.  What happens with you eat excess calories: you gain weight.  In other words, eating excess calories changes gut bacteria, and actually causes more efficient absorption of calories.  A double whammy for dieters.  You’re trying to keep weight off, but you over-eat for a few days, on vacation or during holidays, and Boom – weight gain thanks to excess calories, plus bacteria that effectively push more of those calories into your body.  Interestingly, this effect was not noted in the obese subjects.

What this study did not say:

  • taking probiotic supplements will change your gut bacteria in a way that makes you lose weight
  • eating yoghurt will give you the kind of bacteria that waste calories
  • any particular kind of diet, or specific food, will affect your gut bacteria in a way that causes weight loss, or prevents weight gain
  • eating more fiber or other pre-biotic will change intestinal microbes in a way that keeps you thin.

It’s not that those interventions aren’t possibilities in the future; it’s just that this study did not address those questions.  Obviously the next steps are to figure out whether or not specific diets or foods can affect intestinal microbes in a way that helps with weight loss, or prevents weight gain.  This study just looked at sheer calorie load, keeping the proportions of protein, fats, carbs and fiber constant.  The results, combined with those of the previous study on obese dieters, seems to indicate that eating fewer calories affects bacteria in a way that’s beneficial for weight control.


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