As reported by FoodNavigator, in findings suggesting that people should follow a balanced long-term diet rather than severely restricting their carbohydrate or fat intake, researchers in Japan have discovered that low carbohydrate intake in men and high carbohydrate intake in women are associated with a higher risk of mortality.

Cancer-Related Mortality

The cause and cancer-related mortality, as well as the fact that women with a higher fat intake may have a lower risk of mortality, were revealed by a study conducted by Japanese researchers.

While low-carb and low-fat diets have become popular as a way to promote weight loss and improve blood glucose levels, their long-term effects on life expectancy are less clear.

Researchers from Nagoya University Graduate School of Medicine in Japan conducted a 9-year follow-up survey with 81,333 Japanese individuals (34,893 men and 46,440 women) to evaluate the association between carbohydrate and fat intake and the risk of mortality.

Daily carbohydrate, fat, and total energy intake were estimated using a food frequency questionnaire and calculated as a percentage of total energy intake for carbohydrates and fats.

The quality of carbohydrate intake (i.e., refined versus minimally processed carbohydrate intake) and the quality of fat intake (i.e., saturated versus unsaturated fat intake) were also assessed to examine the impact of food quality on the association with mortality.

Higher fat intake means a lower risk of mortality

Researchers found that men who consumed less than 40% of their total energy from carbohydrates had significantly higher risks of cancer-related mortality and all-cause mortality. This trend was observed regardless of whether refined or minimally processed carbohydrates were considered.

On the other hand, among women with 5 or more years of follow-up, those with a high carbohydrate intake of over 65% had a higher risk of all-cause mortality. No clear association was observed between the intake of refined or minimally processed carbohydrates and mortality risk in women.

For fats, men with a high fat intake of over 35% of their total energy from fats had a higher risk of cancer-related mortality.

They also found that low intake of unsaturated fats in men was associated with a higher risk of all-cause mortality and cancer-related mortality. In contrast, total fat intake and saturated fat intake in women showed an inverse association with the risk of all-cause mortality and cancer-related mortality.

They concluded that this finding does not support the idea that high fat intake is detrimental to women's longevity.

"The finding that saturated fat intake was inversely associated with mortality risk only in women may partially explain the sex-specific differences in associations," said Dr. Takashi Tamura, who led the study.

"Alternatively, factors other than dietary fat from fat sources may be responsible for the inverse association observed between fat intake and mortality in women."

An especially important study

This study is highly important, Tamura emphasizes. Recent studies in Western countries suggest that extreme carbohydrate and fat eating habits are associated with a higher risk of mortality.

Moreover, carbohydrate and fat restriction, such as very low-carb and low-fat diets, are now popular dietary strategies aimed at improving health, including managing metabolic syndrome.

However, this study suggests that low-carb and low-fat diets may not be the healthiest longevity-promoting strategy, as their short-term benefits may be outweighed by long-term risks.

"In general, an unfavorable association with mortality was observed for low carbohydrate intake in men and high carbohydrate intake in women, while high fat intake may be associated with a lower risk of mortality in women," the researchers wrote.

"The findings suggest that individuals should carefully consider how to balance their diet and ensure that they consume energy from a variety of food sources while avoiding extremes."

(Source: Journal of Nutrition - Extreme dietary habits for carbohydrates and fats affect life expectancy: findings from a large-scale cohort study in Japan/DOI: 10.1016/j.tjnut.2023.05.027)