Gut Bacteria Linked to Weight Gain

Jacob Collyer-Smith Lifestyle Writer

A new study1 has highlighted how gut microbiota may influence body weight through its harvesting of nutrients from the food we eat. Changes in diet may have rapid effects on the composition of the guts microbiota, as was found from the analysis of nine obese people and 12 lean people when their diets were changed in terms of the calories they consumed. A previous study, carried out in 2006 by Jeffrey Gordon and his team at the University of Washington, found that gut microbiota populations differed between obese and lean people. He observed that when obese people lost weight the composition of their gut microbiota reverted back to that typically found in lean people, indicating that obesity and microbiota are linked.

Person on weighing scales

Could your gut microbiota influence your weight?

The new study, also involving Jeffery Gordon, offers further insight into the relationship between a persons diet and the composition of their gut microbiota. Lead researcher, Reiner Jumpertz MD, from the National Institutes of Health stated, "Our findings raise the possibility that the gut senses alterations in nutrient availability and subsequently modulated the nutrient absorption... and calorie absorption." Dr Jumpertz and his team observed how the consumption of diets containing 2,400 or 3,400 calories a day affected gut microbiota. The results showed that the changes in nutrient load had rapid consequences on the composition of the bacteria in the gut. The most notable changes were recorded in the two dominant bacteria families in the gut - Firmicutes and Bacteroidetes. Previous studies have shown that weight loss is linked with increased levels of Bacteroidetes and decreased levels of Firmicutes. Dr Jumpertz commented on his findings, "We showed that a high degree of overfeeding in lean individuals was associated with a greater fractional decrease in stool energy loss, which indicated that the degree of overnutrition... may have played a role in the determination of the efficiency of nutrient absorption, and may potentially explain the observation of clearer associations in lean compared with obese subjects enrolled in this study."

Future studies will attempt to alter the make-up of the microbiota in the gut and evaluate how this affects functioning and health of the human host.

See our more recent write-up on a similar topic:

Is your gut bacteria the reason you can't lose weight?


  1. Jumpertz, R. et al (2011) Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humans. American Journal of Clinical Nutrition. Vol. 94, pp. 58-65