Can you lose weight by taking prebiotics?

Picture of Dr. Jen Kerns

Dr. Jen Kerns

Last Tuesday, my horrified dad called me and told me to take down my “poop transplant” post because he thought it was disgusting and not a funny joke. I told him I wasn’t joking. I really wasn’t!

But, for those of us who prefer not to put other people’s poop into our bodies just yet, is there another way to change our own bowel flora to create a microbiome that could help promote weight loss?

The research is still in it’s infancy, really, but several studies have shown that diets with a high amount of fiber (mostly from fruits, vegetables, legumes, and whole grains) are associated with gut flora that do a better job of wasting calories. Prebiotics, which are fiber substances that are indigestible (ultimately reaching the colon where they are fermented by the gut bacteria there), help stimulate the beneficial bacteria. They are found naturally in foods like wheat, asparagus, Jerusalem artichokes, garlic, onions, leeks, and chicory root, and also come in supplements (e.g., the fiber contained in Metamucil Clear & Natural is inulin, which is the fiber derived from chicory root). They can stimulate the “good” bacteria, but can they help abolish the calorie-hoarding bacteria that are found in the colons of obese people, and actually help with weight loss?

As I mentioned last week, there have been studies that have demonstrated that obese people have higher Firmicutes (which have been shown in mice to be better at energy-harvesting — or keeping calories in the body and increasing fat [1]) and fewer Bacteroidetes in their systems than lean people. What is notable is that these alterations can be abolished after a year of diet-induced weight loss, with the degree of change in microbes being proportionate to the amount of body fat lost [2].

Now the question for future research in humans is whether giving obese people prebiotics that will help people lose more weight than they would lose otherwise just from calorie restriction or increased exercise. It’s hard to separate the effect, because many of the foods that people eat when they are trying to lose weight are vegetables that naturally contain prebiotics, so researchers might need to provide one group of dieters a prebiotic in a supplement form while the other dieters get a placebo to see whether there is a difference in weight loss. A promising preliminary study just published in Gut found that obese women who were given a prebiotic supplement containing inulin and oligofructose for 3 months (vs. placebo) had subtle changes in their gut bacteria that could impact obesity and/or diabetes [3]. Now, longer-term studies are needed to evaluate whether prebiotic supplements could actually lead to long-term weight loss and perhaps help prevent the development of diabetes.


1. Turnbaugh, P.J., Ley, R.E., Mahowald, M.A., Magrini, V., Mardis, E.R., and Gordon, J.I. (2006). An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 444, 1027–1031.

2. Ley, R.E.; Turnbaugh, P.J.; Klein, S.; Gordon, J. Microbial ecology: Human gut microbes associated with obesity. Nature 2006, 444, 1027–1031.

3. Dewulf, E. M., Cani, P. D., Claus, S. P., Fuentes, S., Puylaert, P. G., Neyrinck, A. M., . . . Delzenne, N. M. (2013). Insight into the prebiotic concept: Lessons from an exploratory, double blind intervention study with inulin-type fructans in obese women. Gut, 62(8), 1112-1121. doi:10.1136/gutjnl-2012-303304; 10.1136/gutjnl-2012-303304




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