Study highlights role of gut bacteria for ‘nutrient harvest’ and weight gain
Analysis of the gut microflora from nine obese people and 12 lean people showed that the bacterial populations changed as a function of the calories consumed, and these changes occurred within a relatively short period of time.
Finding published in the American Journal of Clinical Nutrition also indicated that the absorption of nutrients was influenced by the gut bacteria.
In 2006, Jeffrey Gordon and his group at the University of Washington in St Louis reported in Nature (Vol. 444, pp. 1022-1023, 1027-1031) that microbial populations in the gut are different between obese and lean people, and that when the obese people lost weight their microflora reverted back to that observed in a lean person, suggesting that obesity may have a microbial component.
The new study – which also involved Dr Gordon – provides another tantalizing glimpse of the interactions between a person’s diet and the composition of his or her gut microflora.
“Our findings raise the possibility that the gut senses alterations in nutrient availability and subsequently modulated the nutrient absorption,” wrote the researchers, led by Reiner Jumpertz, MD, from the National Institutes of Health/ National Institute of Diabetes and Digestive and Kidney Diseases.
“Specifically, the observed association between the gut microbiota and relative stool calories indicates a possible direct role of gut bacteria in calorie absorption.”
In an accompanying editorial in the same journal, Fergus Shanahan and Eileen Murphy from University College Cork said the new study was ‘welcome’.
“There remains no doubt that the proximate cause of obesity is a surplus of energy consumption over expenditure, but the role of diet has become more complex and more intriguing by virtue of its effect on the microbiota and the role of the latter in modifying risk and protection from various metabolic and obesity-related disorders.
“Rigorous pursuit of this question in humans poses significant hurdles, but the report by Jumpertz et al represents a guide post for what may come,” they wrote.
Dr Jumpertz and his co-workers examined how the consumption of diets containing 2,400 or 3,400 calories affected gut bacteria populations.
According to the results, changing the nutrient load in the diets had a ‘rapid’ effect on the composition of bacteria in the gut.
Changes were observed in two of the dominant bacteria families in the gut – Firmicutes and Bacteroidetes. Previous studies have revealed that weight loss is associated with an increase in the latter and a decrease in the former.
The new study revealed that a 20 percent increase in Firmicutes and a decrease in Bacteroidetes (the opposite of what is observed in weight loss) were associated with an increase in the harvest of energy from the diet of about 150 kcal.
“We also 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 relative to individual weight-maintaining energy needs 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,” wrote Dr Jumpertz and his co-workers.
The way forward?
The researchers noted that their study design, which allowed for sample collection of samples in closely monitored individuals, could provide a template for future studies in this area.
The next generation of studies should attempt to deliberately alter the make-up of the microbial community in the gut, how this affects functioning, and how this affects the host human.
Source: American Journal of Clinical Nutrition
2011, Volume 94, Pages 58-65, doi: 10.3945/ajcn.110.010132
“Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humans”
Authors: R. Jumpertz, D. Son Le, P.J. Turnbaugh, C. Trinidad, C. Bogardus, J.I. Gordon, J. Krakoff
Editorial: American Journal of Clinical Nutrition
2011, Volume 94, Pages 1-2, doi: 10.3945/ajcn.111.018473
“The hybrid science of diet, microbes, and metabolic health”
Authors: F. Shanahan, E. Murphy