Many people in Japan, especially young women, are keen to diet.

Every time the mass media introduce a new way of losing weight, they quickly embrace it as a craze, but also quickly lose interest. Recent diet fads have focused on eating bananas and apples and “kanten” (agar). But are people already slender enough?

Following are questions and answers about diet trends in Japan:

Who should diet?

Overweight people should.

According to a 2008 report compiled by the Ministry of Health, Labor and Welfare, 28.6 percent of men in Japan are considered obese, particularly those in their 40s and 50s whose body mass index exceeds 25, the level Japan considers obese.

Women have a lower level of obesity, at 20.6 percent. Women in their 20s and 30s are generally trim, and their BMI is usually lower than 18.5.

But the report showed that 12.6 percent of slender women still try to lose weight, and 52.6 percent of women consider themselves fat.

What about men?

Those who are 40 years old or over might be more keen on dieting since 2008, when the health ministry started including waistline measurements as part of health checks in a bid to curb risks stemming from metabolic syndrome, which can include abdominal obesity, high blood pressure and blood fat disorders.

Men aged 40 and above with an 85 cm waistline or larger and women with 90 cm waistlines or more are deemed at high risk of having abdominal obesity.

But at the same time, 29.8 percent of men categorized as obese are doing little if anything to lose weight, according to the ministry report.

What diets have been popular?

Many people in Japan will focus on a specific food item, especially if it gets heavy media play.

Take bananas. The fruit was first pitched on the popular social networking Web site Mixi in 2006, but when TV shows heaped praise on the fruit’s dietary merits, people cleared the store shelves.

The official Web site by Hitoshi Watanabe, considered the founder of the banana diet, suggests eating the fruit for breakfast with room-temperature water for a chaser. The diet leaves open lunch and dinner for any food item, but says eat dinner before 8 p.m.

Then there’s the cabbage diet, which calls for eating the vegetable in bulk before a regular meal in order to feel full from the start.

Or how about adding some powdered agar into rice, curry or other foods. Agar is low in calories, high in fiber, and helps one feel full quickly, thus offering a weight-loss detox effect.

Apple diets became popular in the 1990s. Eat apples in every meal for three days.

What about exercise?

Exercise is never out of fashion but not necessarily popular.

Recently, however, stretching regimens that help straighten the pelvis have been popular with women and the topic of many books.

By the stretching exercise, experts claim unnecessary fat can be shed.

“Ka-atsu” training is also becoming increasingly popular, especially with men who want to be fit and muscular. Literally meaning “to add pressure,” ka-atsu exercise entails restricting blood flow, reportedly strengthening muscles to a higher degree than can be accomplished in a training gym.

Ka-atsu, however, requires a certified trainer because it can be dangerous, according to the Ka-atsu Training Head Office in Tokyo.

Do popular diets have their critics?

Yes. Junko Abe wrote in “Kiken na Daietto” (“Dangerous Diet”) that although bananas have a detoxifying effect and are rich in potassium, just eating that fruit every morning is not healthy. “You can lose weight by a banana diet, but considering health, you should avoid any type of diet that solely relies on one kind of food,” she wrote.

Erica Angyal, an official nutritionist for Miss Universe Japan, agrees with Abe. “It is important to judge whether the diet (introduced on TV) will be suitable before jumping onto the information. But what I want you to know most is that eating one kind of food is never effective,” she wrote in her book “Sekai Ichi no Bijo ni Naru Daietto” (“The Beauty Diet: Transform Your Life From Inside Out”).

What accelerates diet trends?

In many cases, TV shows have a great impact, particularly “Omoikkiri Ii Terebi” hosted by Monta Mino and “Hakkutsu! Aru Aru Daijiten” broadcast by Fuji TV Network.

After Mino, who is particularly popular with housewives, and “Aru Aru Daijiten” introduced the agar diet, the powder quickly disappeared from supermarkets, but was back after a few months.

There was also a run on bananas after the Tokyo Broadcasting System TV show “Dream Press-sha” related how former opera singer Kumiko Mori, who weighed over 100 kg, lost 7 kg via the banana diet.

The “natto” (fermented soybean) diet was plugged in 2007 by “Aru Aru Daijiten.” Like agar and bananas, supermarkets ran out of natto — at least until it was later revealed that the TV program cooked up false data to sway the audience.

The Weekly FYI appears Tuesdays (Wednesday in some areas). Readers are encouraged to send ideas, questions and opinions to National News Desk