One of the most fascinating studies that has been done in this area involves putting people into an fMRI machine that measures real-time brain activity. Subjects were shown a high-calorie food such as a donut, and the reward centers in their brains instantly lit up compared to when they were shown a low-calorie food like cucumber slices. What happens if you repeat the experiment, but this time, after secretly delivering SCFAs directly into their colons? The subjects reported the high-calorie foods seemed less appealing, and this was matched by decreased activity in some of the reward centers
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