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Obesity on the rise as Japanese eat more Western-style food

by Rowan Hooper

When Japanese people are ordering food, how many times do you hear them asking for “oomori” (large size)? It’s the equivalent of asking for “supersize” in a U.S. fast-food joint.

My guess is that it is only relatively recently, over the last 20 years or so, that oomori has even been a common option in restaurants and food outlets in this country — perhaps someone reading this can tell me when they first heard it.

However, it’s not uncommon these days to hear people lamenting that they are “metabo” (overweight) — a Japanese word derived from the English “metabolic syndrome.”

The fact is that despite the stereotypical view of the Japanese subsisting on fish and rice and miso soup, the national diet is no longer as healthy as it was. Obesity is on the rise. Across the population, current levels are less than 5 percent, which is very low compared to Western countries — but that hides what health practitioners would characterize as an ever-expanding problem.

The Body Mass Index (BMI) — aka the Quetelet Index — is the measure used to determine whether you are overweight or not.

This rule-of-thumb proxy for a person’s percentage of body fat was devised between 1830 and 1850 by a Belgian mathematician and social scientist named Adolphe Quetelet, who was working to develop what he termed “social physics.”

The BMI is arrived at by dividing your weight in kilograms by your height in meters squared (i.e. X kg divided by Y meters × Y meters). For non-metric readers, the same index is arrived at in a rather more complicated manner, by dividing your weight in pounds by your height in inches squared — and multiplying the resulting number by 703.

Although this simply computed BMI has been criticized because it doesn’t take into account differences in body types, it is nonetheless quite probably the best simple index for the job.

In most of the world, a BMI above 30 is taken to mean the person is obese, but the Japanese Society for the Study of Obesity (JASSO) sets that tipping point at 25, because it recognizes that Asians are more susceptible to the health risks of excess fat. By this measure, a startling 20 percent of Japanese are “obese” — a threefold increase from 1962 to 2002 (according to data from the Asia Pacific Journal of Clinical Nutrition, DOI: 10.1046/j.1440-6047.11.s8.19.x).

And there’s more. A broad-based review of Japanese schoolchildren carried out by the National Institute of Health and Nutrition in Tokyo and published in 2004, showed that the prevalence of obesity was on the rise — particularly in rural areas (published in the journal Obesity Research, DOI: 10.1038/oby.2004.27).

So what’s going on? According to Gozoh Tsujimoto, director of the Drug Discovery Research Center at Kyoto University, there is a straightforward explanation for the expansion of waistlines in Japan: Westernization.

“Lifestyle factors have become Westernized,” he told me in an email interview. “Especially, food has become Westernized — and mainly high-calorie and high fat.”

Obesity is the biggest factor leading to diabetes and metabolic syndrome (the name for a group of risk factors that occur together and increase the risk for coronary artery disease, stroke, and type 2 diabetes) — and the prevalence of diabetes has increased rapidly in Japan in recent years.

However, Tsujimoto isn’t one of those Japanese traditionalists simply moaning about Westernization: he is leading efforts to find solutions to the problem.

Tsujimoto’s team at Kyoto is part of an international collaboration that has discovered how a protein called GPR120 could be key to the control of fat levels in the body. People with defects in the protein may be more prone to developing obesity and liver disease when they eat a high-fat diet. Tsujimoto’s team has also found that people with a mutation in the gene that makes GPR120 are significantly more likely to be obese.

Tsujimoto says scientists could develop a drug that mimics the effects of GPR120, and could therefore help to treat and prevent obesity. An account of his work was published last month in the journal Nature (DOI: 10.1038/nature10798).

GPR120, which is found on the surface of cells in the gut, liver and fat tissue, allows cells to detect and respond to unsaturated fatty acids in the diet — that’s the good stuff, like omega-3 fatty acids found in many fish, and which are believed to have a beneficial impact on health. People with defects in the protein can’t respond to omega-3 fatty acids, which normally stimulate fat cells to divide, and it is believed this may contribute to their weight problems.

“Being overweight is not always unhealthy if you can make more fat cells to store fat,” said Philippe Froguel of Imperial College London, who was also involved in the study. “Some people seem to be unable to do this, and instead they deposit fat around their internal organs, which is very unhealthy.

“Our study suggests that in both mice and humans, defects in GPR120 combined with a high-fat diet greatly increase the risk of this unhealthy pattern of obesity. We think GPR120 could be a useful target for new drugs to treat obesity and liver diseases.”

The researchers analyzed the gene for GPR120 in 6,942 obese people and 7,654 controls to test whether differences in the code that carries instructions for making the protein contribute to obesity in humans. They found that one mutation — which renders the protein dysfunctional — raises a person’s risk of obesity by 60 per cent. The researchers think this mutation mimics the effect of a bad diet lacking in unsaturated omega-3 fat.

Tsujimoto says they aim to study more of the variant forms of the GPR120 protein to investigate their role in metabolism.

We’ve heard about potential treatments for obesity before. After all, it’s an urgent problem. Obesity contributes to up to 400,000 deaths per year in the United States, according to some studies, and has been estimated to cost $117 billion per year in that country — which is more than the health costs associated with smoking or problem drinking.

So Tsujimoto hopes the work on GPR120 will help tackle the problem.

In the meantime, he has this advice for people with metabo: “Reduce the fat content of meals; eat meals with increased levels of fiber and plants; eat fish. Also, take moderate exercise and avoid alcohol.”

Rowan Hooper (@rowhoop on Twitter) is the News Editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).”