The roles played by genes in obesity and the potential of effective intervention were discussed at a seminar in Taipei yesterday.
The seminar noted that more than 300 different genes and regions in human chromosomes are linked to obesity, but that the mechanism through which the obesity genes contribute to obesity has not yet been fully explained.
Three protein hormones
secreted under the direction of obesity genes have been found to be associated with obesity in humans in their roles in food intake and body weight regulation, Taiwan Medical University professor of nutrition and health sciences Jane Chao (趙振瑞) said.
Leptin, a protein hormone secreted by fat cells, has an active role in appetite suppression and energy expenditure, Chao said, so the absence or a decreased level of leptin — often caused by aging — leads to increased food intake and thereby weight gain or obesity.
There are also those who are resistant to the effects of leptin, having a high concentration of the hormone, but are still obese.
Adiponectin, another obesity-related protein hormone produced and secreted exclusively by fatty tissue cells, is involved in various metabolic processes such as glucose regulation and the metabolism of lipids.
Ghrelin, on the other hand, is a hunger-stimulating hormone that increases the incentive for humans to eat high-calorie, energy-dense foods.
People found to have a higher level of ghrelin are also more likely to overeat, since they might lack the ability to feel full.
The hormone has thus been an anti-obesity target for obesity therapies, Chao said.
Chao emphasized that while particular gene variations can predispose certain people to obesity, “in most cases, developed after puberty, the contribution made by behavioral and environmental factors is much greater than genetic factors.”
National Chiao Tung University professor of biological science and technology Huang Hsien-da (黃憲達) said the inherited genes contained in DNA cannot be changed.
However, the cells can develop “cellular memory” that can change the gene expression, known as a “epigenetic” change.
In a figurative sense, “obesity has memory, and it takes time to shake it off,” Huang told the seminar.
Huang said that the memory can be twisted through exercise and an improved, healthier lifestyle and diet.
The event was hosted by the Chinese Taipei Association for the Study of Obesity.