Some animal intestines perform an amazing trick. They expand and contract like accordions. This may not sound all that impressive, but its effect on weight can be profound. It allows the body to absorb varying quantities of calories from the same food, depending on the task at hand.----------------------
The mechanism is simple: a ribbon of muscle running the length of the intestine allows it contract and expand. When guts are clenched, they’re shorter, tighter and smaller. When relaxed, they’re elongated.
When intestines are in the longer, stretched-out mode, they expose more surface area to the food passing over them. This allows the cells to extract more nutrients and, therefore, energy. When the intestines shrink back to their shortened state, some of the food passes by essentially unused.
Could a similar accordion-like lengthening and shortening in human intestines underlie some unexplained weight gain in our species? ...there are intriguing clues. Our intestines are also lined with smooth muscle. And we know from autopsies that human intestines are some 50 percent longer after death, when smooth muscle control is no longer exerted. Perhaps, during life, dynamic muscle activity allows the human intestine to vary its calorie-absorbing length in response to medications, hormones, and even stress -- factors frequently pointed to when weight inexplicably increases even when a patient isn’t eating more. Many common drugs cause undesired weight gain through unclear mechanisms. It’s intriguing to consider whether smooth muscle effects of these drugs contribute to ... intestinal stretch leading to greater calorie absorption and weight gain.
Psychiatrists studying eating disorders note that bulimic binge eaters rarely overconsume protein or leafy greens. ...they focus their eating sprees -- sometimes with obsessive intensity -- on sugars and simple carbohydrates.
In the Yale study [of grasshoppers exposed to predatory spiders], the insects’ food choices were driven by external factors beyond their control, in other words, the ecology of fear. In the presence of a predatory threat, they chose foods that would accelerate a lifesaving escape. These animals provide an underexplored possible context for a human binge eater’s food choices. They suggest an evolutionary origin. A stressed person’s decision to forgo the chicken breast and vegetables in his lunch box and consume candy bars instead can seem pointless, weak and even self-destructive. But knowing that some nonhuman animals prefer high-sugar foods when they’re fearful could help a human stress eater better understand his own candy binge. While he knows it’s unhealthy for his waistline, blood sugar, and molars, the impossible-to-resist impulse may spring from a hardwired response to threats that for eons has saved animals’ lives.