Proteins & Nucleic Acids

Mannose Reduces Fat Storage and Improves Energy Usage

“Our results suggest that the gut microbiota contributes to mannose-induced resistance to deleterious effects of a high-fat diet

Obesity is a major risk factor for many chronic diseases, which can be life-threatening, including diabetes, cardiovascular diseases and cancer. Despite the known detrimental health implications, the prevalence of obesity continues to rise in many countries across the world.  

As would be expected, diet is a key factor in the development of obesity, but it appears that the effects of diet may be more far-reaching than just the number of calories ingested.

Research in mice indicates that diet also plays an important role in determining the composition of the gut microbial community. This in turn can affect the functioning of the gastrointestinal tract and overall health.

The gut microbiome is the collective term for the 100 trillion microscopic organisms that thrive in the intestines and provide essential nutrients and energy and help prevent infection. Upsetting the balance of bacteria in the gut can impact gastrointestinal and immune function. Indeed, it has been shown that changes in the gut microbial composition impact a range of host pathways, including energy regulation, systemic inflammation, enteroendocrine signalling, and gut barrier function. Changes in the gut microbiome have also been shown to affect the way we process food and can determine the risk of becoming obese.

The sugar mannose has recently been implicated in obesity as patients receiving it for the treatment of the rare condition congenital disorder of glycosylation (CDG) did not put on weight. This raised the question as to whether it also has an effect on the gut bacterial population.

The effect of mannose on weight gain and the gut microbiome was recently studied in a mouse model of diet-induced obesity. Mice aged up to 8 weeks were fed a normal diet with or without added mannose or a high-fat diet with or without mannose added. The use of energy and fat storage were monitored. The mice were weighed weekly and fat mass was determined every 2 or 3 weeks using a Bruker LF90II TD-NMR spectrometer. Blood sugar levels, liver fat content and overall fitness were also determined.

The data showed that mannose supplementation prevented the mice on a high-fat diet from laying down excessive amounts of fat. Providing mannose thus prevented high-fat-diet-induced obesity in mice. The researchers also showed that glucose tolerance was improved and that the mice were able to use energy and oxygen more effectively. In addition, faecal energy content was higher among mice receiving mannose-supplemented diets, suggesting that they were absorbing fewer calories.

The beneficial effects of mannose, however, were not observed in the older mice, indicating that mannose is required early in life before the onset of obesity in order to provide its protective effects. Once mannose was removed from the diet, the mice started to gain weight again.

The ratio of Bacteroidetes to Firmicutes in the gut microbiome increased in mice receiving extra mannose. The increase was greatest in the youngest mice, reflecting the effects of mannose on weight gain. Similarly, stopping the mannose supplementation restored the original bacterial composition.

This latest study therefore confirms that there is indeed a link between obesity and the gut microbiome.

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Sharma V, et al. Mannose Alters Gut Microbiome, Prevents Diet-Induced Obesity, and Improves Host Metabolism. Cell Reports 2018;24(12):3087-3098. https://www.sciencedirect.com/science/article/pii/S2211124718313688