Japanese schoolchildren are some of the healthiest in the world

Across the developed world, waistlines are expanding. Created by a combination of too much (and the wrong) food and a lack of physical activity, the global obesity epidemic affects children as well as adults.

One developed nation bucks this trend: Japan.

Among 41 developed countries in the European Union and the OECD, Japan is the only country where fewer than one in five children are overweight.

The Japanese diet has long been held up as an example of one of the world’s healthiest. Traditionally, it has contained a variety of fresh ingredients that are sometimes eaten raw, or just lightly cooked. Cooking methods have tended to rely on steaming or simmering.

Another significant reason could be the school meals served to Japanese children. The provision of food to schoolchildren dates back to 1889; rice balls and grilled fish were given to children living in poverty in remote communities in Japan's north. The programme was expanded to cover all of Japan in the aftermath of World War II.

School lunches are an integral part of everyday life for Japanese schoolchildren – not just eating them, but preparing and serving them, too.

Meals are made from local, fresh ingredients – such as baked cod with sweet corn and bok choy, served with minestrone soup and a carton of milk.

The traditional Japanese diet may be falling out of favour due to Western cultural influences. Lifestyle diseases such as atherosclerosis (hardened or congested arteries) and diabetes are on the rise in parts of the country.

UNICEF has highlighted how changes in lifestyle and diet can lead to problems – even changes that seem positive at first.

China is one example of how positive changes to diets can lead to long-term problems. In 1985, 16% of children in China were so malnourished their growth had been stunted. This number fell to just 2% by 2014. This change was due in no small part to the country’s rapid economic transformation and increased urbanization. Eating habits have changed, too, and now include more meat, sugar and fried foods.

This increase in affluence and city-living may have put an end to extreme levels of malnutrition, but not without a cost. Over the same time span, obesity rates in China have increased from 1% to 20%.

The Chinese Center for Disease Control and Prevention has estimated there were 120 million overweight and obese people in the country in 2012. There may be as many as 15 million obese children in China, making it home to one of the world’s largest concentrations of worryingly overweight young people.

Research from the Graduate School of Agricultural Science, Tohoku University, examined the changing Japanese diet and evaluated its nutritional content. A typical Japanese diet in 1975 was less likely to cause diabetes and a build-up of visceral fat among lab rats.

The 1975 diet was identified as being better for promoting a longer and healthier life, too.