By Lisa Rapaport
(Reuters Health) – People who cut back on carbohydrates may end up increasing their risk of premature death if they load their plates with meat and cheese instead of vegetables and nuts, a U.S. study suggests.
While previous research has linked low-carbohydrate diets to better success with short-term weight loss and improvements in risk factors for premature death like diabetes, less is known about the long-term outcomes of cutting carbs, or what types of foods people should eat instead for optimal health.
For the current study, researchers followed more than 15,000 adults ages 45 to 65 for about 25 years. During this period, 6,283 died.
Participants who got 50 to 55 percent of their calories from carbohydrates had a lower risk of death from all causes during the study period than people who had much lower or higher carbohydrate intake, researchers report in The Lancet Public Health.
With lower carb intake, the types of foods people ate instead of carbs were associated with very different types of outcomes.
“Low carbohydrate dietary patterns that replaced carbohydrate with animal-derived protein or fat were associated with greater mortality risk, whereas this association was reversed when energy from carbohydrate was replaced with plant-derived protein or fat,” said lead study author Dr. Sara Seidelmann of Brigham and Women’s Hospital and Harvard Medical School in Boston.
“The key message from this study is that it is not enough to focus on cutting carbohydrates alone, but instead to focus on the types of food replacing them,” Seidelmann said by email.
The study wasn’t designed to prove whether or how eating fewer carbohydrates or more vegetables might directly impact longevity.
But it’s possible plant-based proteins help people live longer by reducing inflammation and so-called oxidative stress, Seidelmann said. As the body uses oxygen, it produces by-products called free radicals that can damage cells and tissues. The damage by oxygen free radicals is known as oxidative stress.
At the same-time, it’s possible the reverse may be true for meats, and especially for processed meats. Animal proteins and fats might have negative health effects because they cause inflammation and oxidative stress, Seidelmann said.
Researchers estimated that from age 50, the average life expectancy was an additional 33 years for people with moderate carbohydrate intake, meaning carbs accounted for 50 to 55 percent of their calories.
High carbohydrate intake – representing more than 70 percent of calories – was associated with average life expectancy of about 32 years. Low carbohydrate intake – representing less than 40 percent of calories – was associated with life expectancy of 29 years.
One limitation of the study is that researchers only assessed eating habits twice, at the start of the study and again six years later, and participants’ diets may have shifted over time.
Even so, the results add to a large and growing body of evidence suggesting that a balanced diet is best, said Andrew Mente, coauthor of an accompanying editorial and a researcher at McMaster University in Hamilton, Ontario.
“The new study shows that a moderate amount of carbohydrates is optimal, while too low or too high was related to mortality,” Mente said by email.
“This is not really surprising given that most nutrients or foods have a sweet spot,” Mente added. “A moderate amount of carbohydrates generally translates into a balanced diet that includes fruit, vegetables, nuts, legumes, fish, dairy and unprocessed meats, all in moderate amounts.”