Gut Flora & Obesity

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Only one in ten of the cells in your body is human. The other 90% are bacteria; we have about 100 trillion of them on us, and in us. The human colon is considered the most biodense ecosystem in the world. We’re just like along for the ride. We exist as one big superorganism, in a mutually beneficial symbiotic relationship—usually.

Collectively, our gut bacteria weigh as much as one of our kidneys, and are as metabolically active as our liver. They affect our immune system; we just found out that if you give probiotics to kids, they don’t get sick as much. Our gut bacteria affect our hormonal balance, and they can affect our energy balance, as well. Is obesity linked to our gut flora?

There are some species of bacteria better at extracting calories from our feces than others. Pooped calories end up in the toilet, rather than on our hips. But there are certain obesity-associated bacteria with an increased capacity for energy harvest. Our bodies are trying to get rid of fecal matter, but certain bacteria in our colon can take our waste, break it down further, and release calories that are then absorbed back into our bloodstream. So here our body is trying to get rid of it all, and the calories are bouncing right back.

Now, this was originally all based on mouse studies, so we really didn’t know what to think. But finally, this year, we have some human data. And indeed, the type of bacteria in our guts is related to body weight, and weight gain.

That got some researchers in Austria thinking. Maybe one of the reasons vegetarians are so much slimmer, on average, is because their diets foster more of the lean-type bacteria, rather than the obese-type. And that’s exactly what they found.

They took a bunch of fecal samples from vegetarians, did some DNA fingerprinting, compared it to omnivore feces, and found significantly more of the lean-type bacteria—suggesting a smaller capacity for energy gain from food in vegetarians. How much smaller? Perhaps 2% of daily caloric intake.

That doesn’t sound like a lot, but it just happens automatically—while we sleep, even, and adds up over time. Over a year, that may come out to about five pounds of fat. And that may not sound like a lot, either, but that’s exactly how much people tend to put on annually during the midlife years.

So that could explain why, as we’ve gone over before, those eating vegetarian don’t seem to get that age-related weight gain that afflicts the rest of the population.

Please consider volunteering to help out on the site.

• G. J. Leyer, S. Li, M. E. Mubasher, C. Reifer, and A. C. Ouwehand. Probiotic effects on cold and influenza-like symptom incidence and duration in children. Pediatrics, 124(2):e172-9, 2009.
• F. Tsai and W. J. Coyle. The microbiome and obesity: is obesity linked to our gut flora? Current gastroenterology reports, 11(4):307-313, 2009.
• An obesity-associated gut microbiome with increased capacity for energy harvest. Turnbaugh PJ, Ley RE, Mahowald MA, Magrini V, Mardis ER, Gordon JI. Nature. 2006 Dec 21;444(7122):1027-31.
• Gut microbiota composition is associated with body weight, weight gain and biochemical parameters in pregnant women. Santacruz A, Collado MC, García-Valdés L, Segura MT, Martín-Lagos JA, Anjos T, Martí-Romero M, Lopez RM, Florido J, Campoy C, Sanz Y. Br J Nutr. 2010 Jul;104(1):83-92. Epub 2010 Mar 8.
• K. Liszt, J. Zwielehner, M. Handschur, B. Hippe, R. Thaler, and A. G. Haslberger. Characterization of bacteria, clostridia and Bacteroides in faeces of vegetarians using qPCR and PCR-DGGE fingerprinting. Ann. Nutr. Metab., 54(4):253-257, 2009.

• bile acids
• bowel movements
• calories
• children
• colon health
• gut flora
• immune function
• metabolism
• microbiome
• obesity
• omnivores
• Plant-Based Diets
• probiotics
• vegetarians
• weight loss