The ability to regulate appetite may decline with age if we overdo the carbohydrates, a recent study suggests.
A team led by Dr. Zane Andrews of Monash University in Victoria, Australia, says that appetite-suppressing cells are attacked by “free radicals” after eating. This degeneration is more significant after meals high in carbohydrates and sugars, and the type of carbohydrate simple or complex seems not to matter.
Dr. Andrews, a neuroendocrinologist previously based at Yale, conducted the study to investigate how the brain responds to ghrelin, a hormone produced in the stomach which induces appetite and operates through a brain region that controls food cravings.
“When the stomach is empty, it triggers the ghrelin hormone that notifies the brain that we are hungry,” he says. “When we are full, a set of neurons known as POMC’s kick in.” He reports that in his research on mice, damage to the POMC neurons from free radicals creates a cellular imbalance between the need to eat and the brain’s signals to stop eating. The same process may occur in humans. So people who consume more carbohydrates and sugars could be experiencing more damage to their appetite- suppressing cells, which could result in overeating and weight gain. People in the age group 25 to 50 are most at risk, according to Andrews, who said that neurons that tell people in the crucial age range not to overeat are being killed off.
This process could play an important role in adult-onset obesity. “A diet rich in carbohydrate and sugar has become more prevalent in modern societies over the last 20 to 30 years,” Andrews said. “This has placed so much strain on our bodies that it’s leading to premature cell deterioration.”
Co-author Dr. Tamas Horvath said the study showed that minute-by-minute control of appetite is regulated by free radicals, implying that if you interfere with free radicals, you may affect eating and satiety.” The free radicals also try to attack neurons triggering hunger, but these are protected by a protein called uncoupling protein 2 (UCP2).
Although the participants in his study were not highly active, Andrews said that exercise, especially aerobic exercise, is important even for people who have highly physical jobs. This research may help explain why athletes tend to put on weight after they retire. It might be more difficult for ex-athletes to feel full due to their high lifetime carbohydrate intake, and so they may overeat. Combined with a more sedentary lifestyle, this pattern could upset the balance of calories consumed versus calories burned.
The team also studied the best time to take antioxidant supplements to control appetite. Research is continuing.
Andrews, Z.B. et al. UCP2 mediates ghrelin’s action on NPY/AgRP neurons by lowering free radicals. Nature, Vol. 454, p. 7204, published online July 30, 2008.