It is one of the great injustices of life: some people have to pay attention to everything they put in their mouths to maintain their weight, while others can eat donuts to the content of their heart and achieve the same result. So what’s the secret? How do some people never get fat?
There is no simple answer to this question, said Kathleen Melanson, professor of food science and nutrition at the University of Rhode Island. “There are genetic, nutritional and even behavioral factors,” Melanson told Live Science, “and the extent to which each of these factors will come into play in a given individual will vary.”
One of the most important factors has nothing to do with the body type, the metabolism or the execution of a spell on a full moon: it is perception. Many people who seem to eat what they want without getting fat are not actually eating more of all of us, said Melanson. For example, your friend who eats ice cream on a daily basis could of course compensate for these extras calories eating less at another meal or having less snacks during the rest of the day. Or maybe, when they eat pizza, they eat slowly, fill up, then stop after a few slices.
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Physical activity can also make a difference, but it doesn’t have to be a gym workout. “Some people move more, even if they aren’t necessarily athletes,” said Melanson. For example, they could get upset or leave, have an active job, or spend the whole day chasing their children. There is also test that some people are genetically predisposed to wanting to move their bodies, Melanson said. This extra movement can also increase the body’s metabolism or how much energy your body spends during the day, excluding exercise. The more you move, the more “the mitochondria inside the muscle cells it will increase in number and in their activity. And those are the power plants that are creating energy, using energy for movement, “said Melanson. More mitochondria means more calories burned.
There is little evidence to suggest that – without exercise – some people were born burning significantly more calories than others, said Dr. Ines Barroso, a researcher from the University of Cambridge in England who studies the genetics of obesity. But there may be physiological differences that allow some people to naturally moderate the number of calories they consume without exercising great self-control, Melanson said. Cascades of nervous system the signals and hormones that circulate in our blood interact to tell us when we are hungry or full. This is called the appetite regulation system and may be more sensitive in some people than others, Melanson said.
An important hormone involved in this system is leptin. It helps regulate the amount of food we want to eat for longer periods of time, not just for our next meal. So a person with a more sensitive system could go back for seconds and thirds to a party, then feel full for the next few days and eat less. “They are able to automatically recalibrate their energy balance because their appetite signaling system can say,” Okay, we have enough energy, “said Melanson.
Genetics can play a role in a person’s tendency to gain or lose weight. The researchers identified over 250 different regions of DNA associated with obesity, according to a 2019 study published in PLOS Genetics. For this study, the researchers compared 1,622 healthy people with low body mass index (BMI) against 1,985 people with severe obesity and 10,433 normal weight control people. They found that lean participants had fewer genes associated with obesity. But according to Barroso, co-author of the study, genes alone do not determine your weight. “We didn’t find genes that protected exclusively from obesity or predisposed someone to obesity. It seemed like a continuum,” said Barroso, “You also have people who have the genetic determinants for obesity, but they are not. [obese]”Barroso said.
In the end, the answer is complex: our tendency to gain weight or maintain our weight is not predetermined, but neither is it entirely under our control. There is no genetic on-off switch that allows some people to eat anything they want without gaining weight; at the same time, the tendency to gain weight isn’t necessarily due to a lack of self-control, Melanson said.
“It’s not the same from one person to another.”
Originally published in Live Science.