Carbohydrates often get a bad rap due to the association of their excessive consumption with weight gain, obesity, metabolic syndrome, and diabetes. This phenomenon, which some researchers call “carbotoxicity” promotes the idea that the excessive consumption of all types of carbohydrates favors the development of chronic diseases. For this reason, many low carbohydrate diets have become popular among people interested in losing weight or managing blood sugar levels. They are even in favor among seasoned athletes. However, several other studies have demonstrated that the quality of carbohydrates that people consume is as important as the quantity. This finding suggests that rather than all carbs being “created equal” some options are better than others for health.
A new study from Nagoya University Graduate School of Medicine in Japan finds that going to extremes with carbohydrates and fats can shorten one’s lifespan. However, the hazard differed for men and women. All the study participants were in fit condition at recruitment. The study found that men who ate too few carbohydrates significantly increased their risk of all-cause mortality. At the same time, women who consumed too little fat had a marginally higher risk of all-cause and cancer-related mortality. The authors of the study paint a complex picture of healthy eating in terms of carbohydrates and fats, overall suggesting that going to any extreme may negatively affect longevity.
The study involved 34,893 men and 46,440 women, ranging in age from 35 to 69 years. The average body mass index (BMI) for men was 23.7, and for women 22.2, within the healthy range. When it came to carbohydrate consumption, the researchers found that, in the study cohort, men who got fewer than 40% of their daily calories from carbohydrates were at a significantly higher risk of all-cause mortality. For women, by contrast, those who got more than 65% of their calories from carbohydrates were at a higher all-cause mortality risk. The researchers found no appreciable difference between the effect of consuming minimally processed carbohydrates versus refined carbohydrates.
Regarding dietary fat, men who got more than 35% of their calories from any kind of fat were at a higher risk of cancer and cardiovascular mortality. In men, when the quality of fat intake was examined, no clear association was observed for saturated fat intake. However, consuming less unsaturated fat was associated with a higher risk of all-cause and cancer-related mortality. For women, consuming more fats — particularly saturated fats — decreased their risk of all-cause and cancer mortality. Some sources of saturated fat include red meat, coconut oil, butter, palm oil and full-fat dairy; other saturated fats are derived from animal sourceslike bacon and processed meats.
Some sources of unsaturated fats, instead, include avocados, olives, pecans and pumpkin seeds. If men require at least 40% of their calories from carbohydrates to avoid reducing their longevity, why might that be, and why might they struggle to obtain the necessary carbs? Scientists suggested that in this study, this is likely due to poor dietary quality, poverty-related lack of adequate healthy care, smoking and alcohol abuse. Beside, diets low in carbohydrates, lack dietary fiber and nutrients such as magnesium, potassium, vitamin C and B vitamins, which are essential for our bodies to thrive. When we lack these protective nutrients, it can increase the risk of some cancers.
The study suggests a shortfall in bioactive dietary components may be at play. Specifically, the authors mention fiber, heme iron, vitamins, minerals, branched-chain amino acids, fatty acids, and phytochemicals as being in short supply. The authors of the study also mention that a diet lacking in plant sources — particularly when animal products make up the difference — has been seen to encourage inflammatory pathways, cause more rapid biological aging, and produce oxidative stress. They suggested that given female participants’ low BMI, it may be likely that they eat less sugar and drink less alcohol, and thus consume higher percent fat compared to the men.
Experts noted the need in women for a certain amount of fat in order to produce adequate hormones like estrogen, which are cardioprotective. Paradoxically, we are taliing about cholesterol, which is the precursor for all the known steroid hormones, and is so feared when it comes with cardiovascular risk and diseases.The authors themselves do not speculate on this, but note that the intake of saturated fat was inversely linked to mortality risk only among women. The study supports the need for further research. For people in the United States and other Western countries, a similar study done with a more locally representative population may provide more actionable findings that consider the local dietary and health landscape.
- Edited by Dr Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Tamura T, Wakai K et al. J Nutr 2023 Aug; 153(8):2352.
Nutrients. 2022; 14(3):554.
J Nutr 2012; 142(9):1713.