Once, obesity was blamed on weak-willed people who tend to overeat. Today, researchers have been looking for possible genetic causes of obesity for about the past 10 years in the hope of discovering clues for defeating this rather formidable enemy.
There are approximately 40 "obesity genes" related to easy weight gain. Changing the order of just one nucleotide base in the DNA base sequence produces a change in an individual's genetic makeup.
The editorial department of The Asahi Shimbun's GLOBE decided to have two reporters test their predisposition to obesity. Cotton swabs were used to collect samples from the mucous membranes in their mouths, then sent to a research facility in Chiba Prefecture. In two weeks, results for 10 genes were returned.
It was discovered that Takaaki Nishiyama, who managed to stay thin even after visiting the so-called "obesity superpowers" of the tiny island nation of Nauru in the western Pacific and the United States, possessed a genetic makeup that made it "quite difficult to gain weight and easy to lose it." He could consume 600 kilocalories above average without needing to do anything to offset the increased intake.
Meanwhile, Akiko Suzuki, who hoped her "large build was due to genetics," was found to have a makeup that made it "somewhat difficult to gain weight." She could consume 250 kilocalories above average without any negative impact. However, it is not possible to clarify everything about a person's predisposition to weight gain/loss through partial genetic testing, and these results only reveal inclinations.
Compared to Westerners, it is said that more Japanese possess genes that tend to store slightly more of the energy received from food intake as fat. People coming to Japan and the American continent from Eurasia during the ice age with its extremely harsh environment carried so-called "thrifty genes." (The hypothesis is that these genes were advantageous to hunter-gatherers as it allowed them to more easily store dietary energy as fat during times of abundance and to burn it when food was scarce.)
It is said that these thrifty genes and a high-fat diet are "the worst possible combination." Half of the adult Pima Indians, an indigenous American population who are known to carry a lot of thrifty genes, suffer from diabetes, with 95 percent of those sufferers deemed "overweight," the result of a modern American diet high in fat.
A case of obesity resulting from genetic mutation was first reported in 1997. The appetites of two children belonging to a Pakistani couple living in Britain were unable to be controlled, causing the 8-year-old daughter to reach 85 kilograms and the 2-year-old son to weigh in at over 29 kilos. Examination revealed a particular genetic mutation that meant the two children lacked a hormone known as leptin.
Leptin is secreted from fat cells and influences the brain's satiety center to suppress appetite and also stimulates the breakdown of fat. However, leptin is a sneaky little hormone. Without it there are problems, but if there is too much, it cannot perform its intended functions. It is believed that many obese people have a high concentration of leptin, and for whatever reason, it does not allow the brain to receive the "I'm full" signal and as a result leaves appetites unsatisfied.
Be that as it may, we cannot blame everything on genes. Kazuo Hara, a physician at the University of Tokyo Hospital, said, "A combination of genes and lifestyle choices causes obesity to occur. It is necessary to comprehensively look at a variety of factors."
It is not easy to definitively state the merits and demerits of gaining weight. A research team belonging to the Ministry of Health, Labor and Welfare examined 50,000 men and women in Miyazaki Prefecture over a 12-year period. It found that life expectancy from 40 was longest for plumper persons with a Body Mass Index (BMI) from 25 to 29 and shortest for persons that were too thin.
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Notes: Weight-gain mechanism and lifestyle-related disease
People gain weight when they take in more energy through the consumption of food than they can burn off through exercise and daily activities.
What kind of foods lead to easy weight gain if overeaten? Protein, even if over consumed, does not accumulate in the body as fat. The problems lie with carbohydrates and lipids (dietary fats).
When carbohydrates such as bread, rice and sugar enter a person's body they are transformed into glucose and glycogen, which serve as sources of energy. However, if more than the required amount of carbohydrates is consumed, it changes into fatty acid and accumulates as subcutaneous and visceral fat.
Lipids, when consumed, are broken down into fatty acid after being absorbed by the intestines and carried to the liver as neutral fats within the blood. During this process, neutral fats that are not used as energy accumulate subcutaneously and in the internal organs.
When an excess of visceral fat accumulates, secretions of antiponectin, a good protein, decrease, resulting in reduced insulin action and an increased risk of diabetes.
Japanese have less subcutaneous fat than Westerners; however, it is thought that they are more likely to accumulate visceral fat. Even if the degree of visceral obesity is small, it is believed that this ectopic (not where it is supposed to be) fat is one of the factors that contributes to a higher risk of developing lifestyle-related disease.
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