There was the first high carb. Then came low carb. Now there is… medium carb.

According to a large, new study, although it may not sound like much, eating carbohydrates in moderation might be the best way to increase longevity.

More than 15,000 Americans were included in the study. They were followed for 25 years. The study found that people who ate a low carb diet (with less than 40 percent of their daily calories coming from carbs) and those who ate high-carb meals (with more than 70% of their daily calories coming through carbs) were more likely to die during the period.

Researchers found that people who eat moderate amounts of carbs have an approximately four-year life expectancy based on their findings. This is compared to those who eat very low-carb.

However, it wasn’t all bad news for those who eat low-carb diets. The second part of The Study was published today (Aug. 16). It examined the effects of replacing carbs with either animal-based proteins or fats. Low-carb diets involving animal-based fats and proteins were associated with higher early death rates. However, low-carb diets containing plant-based protein and fats had a lower risk.

Carbohydrates and long-term health

Numerous studies have shown that low-carb diets can temporarily help people lose weight, but their long-term effects on health are less clear.

The researchers analyzed data from almost 15,500 people aged 45-64 from four North Carolina, Mississippi and Minnesota communities. Participants completed questionnaires about what foods they ate, how often, and when they did it, both at the beginning of the study in the late 1980s and six years later.

Participants were tracked for approximately 25 years. During that time, 6,283 people died.

Researchers found that the relationship between carb intake and life expectancy was U-shaped. This means that low- and high-carb diets were associated with higher death rates, while moderate-carb diets had a lower death rate.

To perform an additional analysis that included more than 432,000 participants in 20 countries, the researchers drew data from seven other studies and their own. This analysis confirmed the earlier findings of the researchers: A 20% increase in death risk was found for low- and high-carb diets compared to moderate-carb diets.

The analysis found that low-carb diets were more important than the source of fats and proteins. A higher risk of death was associated with diets that replace carbs with protein and fats from animals, such as beef, lamb and pork, chicken, and cheese. However, diets that substitute carbs for proteins and fats from plants, such as vegetables and legumes, have a lower death rate.

Study caveats

Researchers noted that the study did not find a causal link and that it didn’t prove that high-carb or low-carb diets caused the rise in early mortality. The study only examined people’s diets two times over 25 years. Participants’ diets may have changed, which could have affected their results.

These limitations aside, a U-shaped relationship between diet and health outcomes is possible. Dr. Andrew Mente of McMaster University and Dr. Salim Yasuf from the Population Health Research Institute, Hamilton, Canada, wrote in a commentary to accompany the study. This is referred to as a “sweet spot”. (Mente, Yusuf and Yusuf weren’t involved in the new research.