Controversy has been growing about the safety and effectiveness of diets that limit the intake of carbohydrates, which have become popular treatments for diabetes and weight loss.
While such diets have proven highly effective, medical experts have voiced concern about the potential adverse health effects in the long term.
As a result, the Japan Diabetes Society has started working on a set of guidelines.
The term "carbohydrates" mainly refers to foods with a high sugar or starch content, such as rice, bread and potatoes. People who are following a carbohydrate-restricted diet try to limit their intake of carbohydrate-rich foods or avoid them altogether.
Though artificial sweeteners are also a type of sugar, dietary experts say people limiting their intake of carbohydrates can consume them because they do not raise blood sugar levels.
According to the theory, zero or reduced intake of carbohydrates prevents blood sugar levels from rising rapidly after eating. Thus the levels are stabilized, which helps control diabetes symptoms.
Insulin, a hormone that lowers blood sugar, also causes the body to store fat. If the body secretes less insulin, it can result in weight loss.
The concept of limiting one's intake of carbohydrates has existed since long ago.
However, the leading dietary theory among medical societies had been that total calorie intake should be restricted. The theory of limiting the intake of carbohydrates was viewed with skepticism.
But in the 2000s, many reports began appearing overseas that the method was effective for weight loss and stabilizing blood sugar levels, which attracted the attention of health experts.
In 2008, the American Diabetes Association recognised the method as a legitimate dietary treatment.
The problem is there are no standards on the degree to which carbohydrates should be limited or how the treatment should be carried out.
Koji Ebe, the director of Takao Hospital in Kyoto, is Japan's pioneer of the method, and has written many books on the subject. He advocates the strictest option.
Usually one meal contains 80 to 100 grams of carbohydrates. The treatment proposed by Ebe reduces carbohydrates to 10 to 20 grams.
Because carbohydrates are also found in leafy vegetables and beans in addition to potatoes, most practitioners of this option eat little to no grains.
In 2006, many reports surfaced overseas that practitioners of the method had become dangerously ill because their extreme limits on carbohydrates had resulted in a surplus of ketone bodies, which are by-products of fat decomposition.
Recently, medical experts have reported that continuing the method over a long period of time increases the risk of strokes and heart attacks.
The American Diabetes Association recommends the method be followed for up to two years. Some doctors specialising in diabetes treatment in Japan recommend dieters consume a small amount of grains, or about 20 to 40 grams of carbohydrates per meal.
Medical experts agree the method should never be applied to patients with weak kidney functions, and that it can cause increased risk of hypoglycemia in patients taking medicine to lower blood sugar levels.
However, experts' opinions are divided over whether the method can be applied to pregnant women and type-1 diabetes patients who are unable to secrete insulin.
There is also an option that allows unrestricted consumption of meat and fat, and another risky way in which people stop taking medications based on their own judgment of their health.
Given the potential adverse health effects, Takashi Kadowaki, chairman of the Japan Diabetes Society and director of the University of Tokyo Hospital, in July issued a rare statement warning about the dietary method.
The statement said, "Extreme limits on the intake of carbohydrates may even result in death, and we don't recommend [following such methods]."
At the same time, the society said the method does not damage health if it is applied moderately based on clinical studies in other countries. It plans to create guidelines detailing safe ways of applying the method.
But doctors who are now recommending the method had doubts. One of them said, "Is it effective to limit the intake by only a small quantity of carbohydrates?"
In fact, there are only a few studies about the effectiveness and safety of the method on Japanese.
The society said it will consider implementing such studies in Japan and will listen to the opinions of outside experts and ordinary citizens.