There is a view that certain nutrients, such as fats, carbohydrates, etc. are the main causes of the obesity epidemic. But Kevin Hall, director of the Integrated Physiology Department at the Center for Diabetes, Digestive and Kidney Diseases in the United States, has tested other causes for the obesity epidemic.
Experiments do not support fat and carbohydrate cause obesity
Kevin Hall once agreed that certain nutrients can lead to obesity, especially carbohydrates. “Carbohydrate intake increases insulin in the blood, and insulin levels affect fat storage and fat cells. “But the truth is not true, so I decided to study it. “
As a result, Hall conducted two rigorous small-scale studies that did not support the traditional view that fat and carbohydrates lead to obesity. In both studies, volunteers were hospitalized for several weeks and strictly controlled for food. The goal was to avoid multiple deviations in a typical dietstudy, where volunteers reported their own diets that were not consistent with what they actually ate.
His first study found that reducing carbohydrate intake actually slows down body fat consumption, a result that is quite different from previous predictions. In a second study, he found new causes of weight gain. When volunteers ate their favorite foods according to their wishes, Hall found that volunteers who ate over-processed foods consumed more than 100 calories. In just two weeks, the former will gain about a kilogram of weight.
Hall said the studies strongly prove that the main reason for the increase in obesity is that producers over-process food and have little to do with nutrients.
Over-processed foods can disrupt intestinal and brain signals
Why do most people love over-processed foods? Dana Small, a neuroscientist and professor of psychiatry at Yale University, believes she has found some clues by studying the effects of overprocessed foods on brain circuits.
She notes that nerve cells in the gut send signals to the brain through vagus nerves. These signals contain information about how much energy the stomach and intestines consume. If the signal is disturbed, the chaotic signal can cause people to overeat.
After studying the brain through imaging techniques, Small and other scientists found that high-calorie foods contain smells, colors and tastes that activate the striatum in the brain, and that decisions related to the striatum include how much food to eat.
That’s the problem with over-processed foods, Says Small. When eating these foods, the body consumes energy that is inconsistent with the energy it perceives, which causes confusion in the brain’s signals and leads to more food intake. For example, natural sweeteners such as honey, maple syrup and edible sugar all contain certain calories. They prompt the brain to expect sweetness and signal how many calories it needs to eat. However, artificial sweeteners such as saccharin, without adding energy, can cause the brain to expect and experience sweetness. When you don’t consume the expected calories, the brain feels a little less, prompting people to keep eating.
“Hall has proven that eating over-processed foods eats more,” Small stressed. My point is that overprocessed foods don’t give the brain metabolic signals when it eats low-processed foods, so they don’t record total calories, which leads people to eat more. “
Animal trials confirm the theory that eating over-processed foods blocks intestinal signals, which affect the brain’s perception of food and total intake as a whole, Smol said. “In nature, for example, carbohydrates are always with fiber,” she says. In overprocessed foods, fiber may not exist, or the fiber steam is entirely man-made. “Natural foods rarely have both carbohydrates and fats, and they often coexist in overprocessed foods. We make countless delicious foods out of fat, sugar, salt and additives, and we love them. But they don’t necessarily have a feeling of satiety, but they can provoke an appetite.
Eating large amounts of overprocessed foods can alter brain circuits and increase the brain’s sensitivity to food signals, said Kent Berich, a professor of psychology and neuroscience at the University of Michigan. He demonstrated this effect through rodent experiments. “When junk food is fed to rats, some rats gain weight, while others don’t. The dopamine system in mice that gained weight changed, became more sensitive to food signals, and was particularly fond of junk food. They don’t show more pleasure, but they do have more cravings, which drives them to more foraging behavior. “
But not all of the researchers agree with Hall that over-processed foods are the leading cause of obesity. “Over-processed foods can lead to overeating, but there’s not enough evidence to support that conclusion,” said Rick Mattis, a professor of nutritional scienceate at Purdue University and the new director of the American Academy of Nutrition. I think that the way food is made may not be the main reason the brain reacts to it, but the nutritional content of food is a more relevant driving force. “
Written by Ellen Rapper Schell
Translation: Zhai Dawei
Source: Global Science