A lot of people looking to lose weight are trying low-carb diets such as Keto or Atkins, but in doing so they may be shaving years off their lifespan. According to a 25-year-long study, individuals whose diets were either low or high in carbohydrates had a higher risk of death than those who consumed a moderate amount of carbs. Another important finding was that switching meat for plant-based protein led to healthier outcomes, in people with low-carb diets.

Pasta is a high-carb dish. Credit: Pixabay.

For their study, researchers followed 15,428 American adults aged 45-64 years from 1987 until 2012. The participants had to self-report their diets, based on which the researchers estimated the proportion of calories they got from carbohydrates, fats, and protein.

After correlating health outcomes with diet, researchers found that, over a 25-year period, people who had a moderate carbohydrate intake (50-55% of daily calories) had an average life expectancy of 83 years — that’s four years longer than those with low carb intake (40%), who lived only 79 years on average. Participants with a high carb intake (more than 70% of daily calories) had an average life expectancy of 82 years, slightly lower than the moderate carbs intake group.

Carbohydrates include foods such as fruit, vegetables, and sugar but most often people ingest the most carbs from starchy foods such as potatoes, rice, and pasta.

The researchers at the Brigham and Women’s Hospital, Boston, then compared low-carb diets rich in animal protein and fats with those that contained lots of plant-based protein and fat. They found that the latter diet slightly reduced the risk of death.

Low-carb diets that replace carbohydrates with protein or fat are becoming increasingly popular. The new study published in The Lancet, however, suggests that people ought to be more careful and shouldn’t jump on the latest diet fad before doing proper research.

Although previous randomized trials have shown low carbohydrate diets are beneficial for short-term weight loss and improve cardiometabolic risk, this study shows that low-carb dieting may shorten lifespan if done for many years.

“We need to look really carefully at what are the healthy compounds in diets that provide protection”, says Dr. Sara Seidelmann, Clinical and Research Fellow in Cardiovascular Medicine from Brigham and Women’s Hospital, Boston, USA who led the research.

“Our data suggests that animal-based low carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall lifespan and should be discouraged. Instead, if one chooses to follow a low carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy aging in the long term.”

In the same study, the authors also performed a meta-analysis of data from eight prospective cohorts involving 432,179 people in North American, European, and Asian countries. The analysis revealed similar trends — participants whose diet consisted of high and low in carbohydrates had shorter life expectancy than those with moderate consumption.

“These findings bring together several strands that have been controversial. Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate,” says Walter Willett, Professor of Epidemiology and Nutrition at Harvard T. H. Chan School of Public Health and co-author of the study.

As a caveat, there are some limitations to this study. The conclusions are associations not causal relationships and the researchers had to rely on the participants to remember what they had eaten in order to determine their diets. The food questionnaire in the study may have also led some people to underestimate the calories and fat they had eaten. More research will likely follow but, in the meantime, it may be a good idea to stay away from low-carb diets.