When we eat, our blood glucose levels rise temporarily. Our blood glucose receptors perceive this change and signal the brain that the body has consumed enough food. It takes about 20 minutes for this signal to reach the brain. Therefore, it's easy to pass the point of satiation without realizing it.
This problem is especially acute for fast eaters. Within the 20-minute duration, they can consume a lot of food, many more calories than they really need, leaving them with an uncomfortable, bloated feeling. If they had chewed and eaten slowly, they wouldn't have ingested as much food by the time the brain transmitted the "full" signal.
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