Low-carb diets may shorten lifespan, new study says
Low carbohydrate diets are popular in the diet industry, though a new study published in The Lancet Public Health suggests diets restricting carbohydrate intake may shorten a person’s life by up to four years.
In what authors are calling "the most comprehensive study of carbohydrate intake,” the observational study looked at 15,428 adults aged 45–64 years old in four U.S. communities from the Atherosclerosis Risk in Communities Study (ARIC). Researchers found that diets both low in carbohydrates, less than 40 percent, and high in carbohydrates, less than 70 percent, were linked to an increase in mortality. Moderate carbohydrate consumption, 50-55 percent, had the lowest risk of mortality, according to the study.
The primary findings, confirmed in a meta-analysis of studies on carbohydrate intake including more than 432,000 people from over 20 countries, also suggest that not all low-carbohydrate diets appear equal: eating more animal-based proteins and fats from foods like beef, lamb, pork, chicken and cheese instead of carbohydrate was associated with a greater risk of mortality. Alternatively, eating more plant-based proteins and fats from foods such as vegetables, legumes, and nuts was linked to lower mortality.
"We need to look really carefully at what are the healthy compounds in diets that provide protection,” says Sara Seidelmann, PhD, lead researcher and a clinical and research fellow in cardiovascular medicine from Brigham and Women's Hospital, Boston, Massachusetts.
Previous randomized trials have shown low carbohydrate diets are beneficial for short-term weight loss and improve cardiometabolic risk. However, the long-term impact of carbohydrate restriction on mortality is controversial with prospective research, so far producing conflicting results. Further, earlier studies have not addressed the source or quality of proteins and fats consumed in low-carb diets.
The findings show observational associations rather than cause and effect. Considering evidence from other studies, the authors speculate that Western-type diets that heavily restrict carbohydrates often result in lower intake of vegetables, fruit, and grains and lead to greater consumption of animal proteins and fats—some of which have been implicated in stimulating inflammatory pathways, biological ageing, and oxidative stress—and could be a contributing factor to the increased risk of mortality. High carbohydrate diets, common in Asian and less economically advantaged nations, tend to be high in refined carbohydrates such as white rice, may also contribute to a chronically high glycemic load and worse metabolic outcomes.
The authors note some limitations, including that dietary patterns were based on self-reported data, which might not accurately represent participants' food consumption; and that their conclusions about animal-based sources of fat and protein might have less generalizability to Asian populations, which tend to have diets high in carbohydrates, but often consume fish rather than meat. Finally, given the relatively small number of individuals following plant-based low-carb diets, further research is needed.