Gut flora need fibre

_{Amended by the author 06/07/2016}

The activity of our gut bacteria plays an important role in supporting good health and may hold the key to combating the growing obesity crisis.

We already know from multiple studies that bacteria in the gut produce a compound called propionate when they break down dietary fibre. Some people’s gut bacteria may naturally produce less propionate than others, which may be why some people seem more naturally predisposed to weight gain.

Our research group at Imperial College London teamed up with researchers at the University of Glasgow to conduct the first study in humans to investigate the effect of propionate on areas of the brain which are known to be involved in reward and food cravings. The results of this study have just been published in the July edition of the American Journal of Clinical Nutrition.

We used a unique dietary supplement, called inulin-propionate ester, which delivers a large amount of propionate directly to the colon. We estimate that the 10 g dose of the inulin-propionate ester used in this study increases the average person’s daily propionate production by 2.5 times.

We recruited 20 healthy men and asked them to consume a milkshake with a light breakfast that either contained the inulin-propionate ester supplement, or inulin on its own as a control. The male subjects were assigned the milkshake in a random order and did not know which one they had consumed. A week later, we invited the same subjects back and repeated the study protocol with the other milkshake, so we could compare our results.

After a period of 5 hours, when we were sure that the milkshake contents had been digested, we asked each person to look at images of a range of low or high-calorie foods that included salad, fish and vegetables or chocolate, cake and pizza and rate how attractive they found them. At the same time, we measured their brain activity using functional MRI in order to assess whether certain areas of the brain associated with food cravings were more or less active.

We found that when volunteers drank the milkshake containing the inulin-propionate ester, they had less activity in two areas of their brain linked to reward. These areas, called the caudate and the nucleus accumbens, found in the centre of the brain, have previously been linked to food cravings and the motivation to want a food. In the caudate, this reduction in activity was driven specifically by a lowering of the response to the high-calorie food pictures.

When the volunteers drank the milkshake with the inulin-propionate ester supplement they also rated the high-calorie food pictures as less appealing.

Finally, the volunteers were given a bowl of pasta with tomato sauce, and asked to eat as much as they liked until they felt comfortably full. When the participants drank the inulin-propionate ester, they ate 10 per cent less pasta than when they drank the milkshake that contained inulin alone.

So, it looks like the inulin-propionate ester significantly reduces cravings for high-calorie foods and may be used as a supplement in the future to help maintain a healthy body weight. This study illustrates the important role the gut microbiota plays in appetite regulation and food choice.

_{“Increased colonic propionate reduces anticipatory reward responses in the human striatum to high-energy foods” by Byrne et al. is published in the July edition of The American Journal of Clinical Nutrition}