Japan is often cited as a proof that a high carbohydrate diet is the solution to avoid chronic diseases. I think it is a misguided belief.
In the 1950s, Ancel Keys considered his hypothesis (dietary fat causes heart disease) confirmed by the example of Japan, where people ate a low-fat diet, had low cholesterol levels, and had very little incidence of heart disease. It is true. It is also true, that at that time, sugar consumption was also very low and carbohydrates (brown rice, millet, buckwheat, etc) were not processed. So, we could also say that the low incidence of heart disease was a result of the lack of sugar and refined carbohydrates in their diet. Of course, Keys paid no attention to sugar consumption.
In the same time, the fact that Japanese men in California still had very low cholesterol levels, but died of heart disease, was largely ignored.
"Any research that did not support [his] hypothesis was said to be misinterpreted, irrelevant, or based on untrustworthy data. Studies of Navajo Indians, Irish Immigrants to Boston, African Nomads, Swiss Alpine farmers, Benedictine or Trappist monks all suggested that dietary fat was unrelated to heart disease, These were explained away or rejected by Keys."
- Gary Taubes
Now, I do not call "science" selecting evidence only in support of a hypothesis.
The Honolulu Heart Program, where researchers followed up 7300 men of Japanese descent, concluded that those who ate less fat, had a higher incidence of heart disease than those who ate more fat. This, obviously posed a dilemma for dietary advice.
"By the mid-1990s, however, the Japanese contingent of the Seven Countries Study, led by Yoshinori Koga, reported that fat intake in Japan had increased from the 6 percent of calories they had measured in the farming village of Tanushimaru thirty-five years earlier, to 22 percent of calories. 'There have been progressive increases in consumption of meats, fish and shellfish and milk,' they reported. Mean cholesterol levels rose in the community from 150 mg/dl to nearly 190 mg/dl, which is only 6 percent lower than the average American values (202 mg/dl as of 2004). Yet this change went along with a 'remarkable reduction' in the incidence of strokes and no change in the incidence of heart disease. In fact, the chance that a Japanese man of any particular age would die of heart disease had steadily diminished since 1970. "It is suggested that dietary changes in Tanushimaru in the last thirty years have contributed to the prevention of cardiovascular disease," Koga and his colleagues concluded."
- Gary Taubes
Here again, dietary fat intake is unrelated to the incidence of heart disease, but low dietary fat intake is related to higher risk of stroke.
It is interesting to note, that in the 1980s, Japanese physicians recommended their patients to raise their cholesterol levels (quite the opposite of what is still recommended in the United States), as they have noticed that low cholesterol levels were associated with a higher incidence of stroke.
The bottom line is that dietary fat has little to do with the development of chronic diseases.
"Belief in saturated fat and cholesterol as killers achieved a kind of critical mass when anti-fat, anti-meat movements evolved independent of science."
- Gary Taubes