Is a low-carb diet or low-fat diet better for a longer life?

Consuming a low-fat diet full of healthy foods during middle age may lengthen your life, a new study suggests.

In contrast, a healthy low-carbohydrate eating pattern did not lead to much improvement in longevity, according to the analysis of dietary data from more than 370,000 middle-aged and older adults published in the Journal of Internal Medicine.

“Following a healthy low-fat diet with minimal intake of saturated fat can be an effective approach to promoting healthy aging among middle-aged and older individuals,” says lead study author Yimin Zhao, Ph.D., researcher in the department of epidemiology and biostatistics at Peking University’s School of Public Health.

“The results from our study suggest that both fat quantity and quality are important determinants of health effects in middle-aged and older people,” Zhao told via email. “We recommend that people should limit fat intake, even if they are trying to only consume healthy fat.”

The new study comes on the heels of a new evaluation of popular diets by the American Heart Association, which rated DASH, Mediterranean, vegetarian and pescatarian diets as the most heart healthy, while giving mid-range scores to low-fat and low-carb diets.

Low-carb versus low-fat diets

To take a closer look at the impact of low-fat and low-carb diets on longevity, Zhao and his colleagues analyzed data from the NIH-AARP Diet and Health Study, which in 1995 and 1996 recruited AARP members ages 50 to 71 from six states: California, Florida, Pennsylvania, New Jersey, North Carolina and Louisiana. For that study, researchers asked participants to fill out a 124-item food questionnaire.

For their analysis, Zhao and his colleagues excluded participants who reported having cancer, heart disease, stroke, diabetes, end-stage kidney disease, poor health status, needed someone to fill out the questionnaire for them, or ate an extraordinarily high number of calories , which left 371,159 participants. The researchers then categorized their food choices based on how closely they resembled a healthy low-carb or healthy low-fat diet.

A healthy low-carb diet was defined as a high intake of unsaturated fats with limited consumption of low-quality carbohydrates, such as refined grains, added sugars, fruit juice and starchy vegetables. A healthy low-fat diet includes plant-based proteins, limited saturated fat and high-quality carbohydrates, such as whole grains, whole fruit, legumes and non-starchy vegetables, Zhao said.

During a median follow-up of 23.5 years, 165,698 of the participants died. The researchers found that participants whose eating patterns most closely resembled the healthy low-fat diet had an overall mortality rate that was 18% lower than those with eating patterns that least resembled the healthy low-fat diet. Those whose eating patterns most closely resembled the healthy low-carb diet had only a slightly lower mortality rate compared to those with eating patterns that least resembled this diet.

But there are limitations to these findings, despite the strong data analysis, says Linda Van Horn, Ph.D., chief of nutrition at Northwestern University’s Feinberg School of Medicine, who wasn’t involved in the research. She points out the data used is 20 years old, when “people had a very different understanding of diet and nutrition,” she tells

What’s more, she believes the results are lacking in an important context around participants’ overall health. “My major concern is that nowhere do they talk about obesity or what conditions these people are in,” Van Horn says. “We don’t know what their physical activity level was. We don’t know what their BMI was.”

Replacing carbohydrates and fats

Dr. Matthew Tomey, cardiologist and assistant professor at the Icahn School of Medicine at Mount Sinai in New York, agreed, telling the researcher did “an admirable job with the data.”

What matters most when people choose a low-fat or low-carb diet is what they replace the fat or carbs with, explains Tomey, who wasn’t involved with the new research. People’s choices can be “adaptive or maladaptive,” he adds.

He points to the period of time where fat was demonized and people replaced it with lots of carbs, often unhealthy ones. Moreover, he notes, other factors can play a big role in people’s overall health: sleep patterns, weight, blood sugar, blood pressure and cholesterol.

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