Researchers at Duke University in North Carolina claimed that the human brain senses that such foods are high in calories and reward people by releasing hormones that make them feel happier. Ivan E de Araujo of the university's medical centre, who led the study, said they had identified a calorie-sensing system in the brain. The team studied mice that had been genetically altered to make them unable to taste the sweetness in food. It found that the animals' internal ''reward'' system was activated by sweet, high-calorie foods despite the animals' inability to taste them. Reactions in the part of the brain that controls rewards increased with the intake of more such food. The study could offer insights into the causes of obesity as understanding why high-calorie food triggers such a response in the brain could hold the secret to turning off the pleasurable feelings associated with eating sweet food.