Coffee and tea both contain methylxanthine compounds such as caffeine, theobromine and theophylline, that have been identified as potentially beneficial for weight loss. In addition, green tea contains a number of flavan-3-ol compounds that have been shown to aid weight loss. Coffee beans also contain a form of indigestible polysaccharide called mannooligosacharides (MOS) that are known to be a prebiotic agent in humans. Studies show that MOS are resistant to α-amylase, and remains undigested as they passes through the upper gut. Fermentation of MOS begins in the large intestine, where they are converted into short chain fatty acids by colonic bacteria. These short chain fatty acids can be absorbed and used as an energy source. In this way MOS are similar to fructooligosaccharides (FOS) found in other food sources. Animal and humans studies indicate that consumption of MOS may decrease total body fat.
To test the weight loss effects of MOS on humans, researchers1 fed 50 men and women with a body mass index of between 27 and 33 km/m2 either a beverage containing 4 grams of MOS or a placebo containing no MOS. Magnetic resonance imaging was used to assess body fat at baseline and endpoint, and blood pressure and feelings of appetite and satiety were taken weekly. Men consuming MOS in their beverage had a significant reduction in total body volume (-3.0%) compared to the placebo (0.0%). Total reductions in adipose tissue also tended to be lower in the men consuming MOS (-3.0%) compared to the placebo (-2.1%). Men consuming MOS also tended to have larger reductions in subcutaneous adipose tissue (-3.0%) compared to the placebo (-2.0%). Women did not show any significant changes between the treatment and placebo groups.
These results suggest that some of the weight loss effects of coffee might be accounted for by the presence of MOS. It is not clear why consumption of MOS might cause weight loss in humans, but some evidence suggests that short chain fatty acids produced by bacterial fermentation may have appetite suppressing effects. Short chain fatty acids are readily used as energy, and this may have a regulatory effect on further energy intake. However, in this study no differences in appetite were reported by the study participants between the treatment and placebo groups. Alternatively, increased production of short chain fatty acids may decrease de novo lipogenesis in the liver, thus interfering with normal fat metabolism. Interestingly the MOS had no significant effect on women, which suggests gender differences in the metabolism of fat, which may be accounted for by hormonal physiology.
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