How Low Carbs Can Decrease Your Lifespan

Scientists uncovered the link between carbs and longevity: men who consume low amounts of carbohydrates and women with high carbohydrate intake are at a higher risk of death.

While high fat intake is associated with decreased longevity in men, women who consume more fat tend to live longer.

Researchers at Nagoya University Graduate School of Medicine in Japan examined data from 81,333 Japanese individuals (34,893 men and 46,440 women) aged between 35 to 69. The average body mass index was 23.7 for men and 22.2 for women, falling within the healthy weight range. The participants were followed up for over nine years.

Daily dietary intakes of carbohydrates, fats, and total energy were estimated using a food frequency questionnaire. Researchers also assessed the quality of carbohydrate intake, such as refined compared with minimally processed, and the quality of fat intake, with saturated fat indicating low quality compared with high-quality unsaturated fat.

The study, published in The Journal of Nutrition, found:

  • Men who consumed less than 40% of their total energy from carbohydrates were at significantly higher risks for all-cause and cancer-related mortality, regardless of the quality of carbohydrates.
  • Women with a high carbohydrate intake, with carbs making up more than 65% of their diet, had a higher risk of all-cause mortality. The quality of carbohydrates they consumed did not appear to affect the mortality risk.
  • The risk of cancer-related mortality was higher among men who got more than 35% of their total energy intake from fats. Additionally, low unsaturated fat intake in men was linked to a higher risk of all-cause and cancer-related mortality.
  • In women, higher fat intake was associated with a lower risk of all-cause mortality, suggesting that fat consumption may not have harmful effects to longevity in women.

The finding that saturated fat intake was inversely associated with the risk of mortality only in women might partially explain the differences in the associations between the sexes. Alternatively, components other than fat in the food sources of fat may be responsible for the observed inverse association between fat intake and mortality in women.

- Takashi Tamura, lead author of the study

Extremely low-carbohydrate and low-fat diets are popular dieting strategies to improve health, including managing metabolic syndrome. However, the study authors warn that long-term risks could potentially outweigh the short-term benefits of such diets.

Carbs and longevity

Scientists have previously tried to determine the link between carbs and longevity. For example, a 2019 study published in the European Heart Journal found that participants with the lowest carbohydrate intake had a 32% higher risk of overall mortality and a 36% higher risk of cancer-related mortality. The risk was highest in those not considered obese.

Another study published in the Lancet in 2018 associated a low carb intake of less than 40% of total energy and high carbohydrate intake, with carbs accounting for more than 70% of the diet, with increased mortality. A diet where carbohydrates make up 50% to 55% of total energy was found to be optimal for longevity.

The findings of both of these studies conducted in Western populations are consistent with the new study in Japanese individuals who typically have relatively low fat and high carbohydrate dietary intakes.

Carbohydrates, along with fat and protein, are macronutrients that comprise the human diet. There are three types of carbs:

  • Sugars, such as the natural sugar in fruit and milk or the added sugar in soda and processed foods.
  • Starches, including wheat, oats, and other grains, as well as starchy vegetables, lentils, and peas.
  • Fiber, the part of plant foods that isn’t digested.

Carbohydrates are often vilified, although they provide energy for the body and are an excellent source of various nutrients. For maximum health benefits, choose healthy carbs, such as whole grains, vegetables, whole fruits and 100% fruit juices with no added sugar, beans and legumes, and low-fat or non-fat dairy products.

At the same time, consider limiting the intake of unhealthy carbs, including white bread, polished rice and flour, sweets, and sugar-sweetened beverages.

The new study suggests that a balanced diet rather than heavy restriction of carbohydrate or fat intake may increase longevity.

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