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 of an 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 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 tells TODAY.com 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 included plant-based proteins, high-quality carbohydrates, such as whole grains, whole fruit, legumes and non-starchy vegetables, and limited saturated fat, 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, Linda Van Horn, Ph.D., chief of nutrition at Northwestern University’s Feinberg School of Medicine, who wasn't involved in the research, tells TODAY.com. She points out that the data used is 20 years old and from when "people had a very different understanding of diet and nutrition.”
She also believes the results are lacking important context around participants' overall health. “My major concern is that nowhere do they talk about obesity or what condition these people were in,” Van Horn says. “We don’t know what their physical activity level was. We don’t know what their BMI was."
Replacing carbs and fats
Dr. Matthew Tomey, cardiologist and assistant professor at the Icahn School of Medicine at Mount Sinai in New York, agrees, telling TODAY.com the researchers did “an admirable job with the data.”
But 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. He points to the period of time where fat was demonized, and people replaced it with lots of carbs, often unhealthy ones.
"The reality is that we don’t always compensate in calorie-neutral ways for the deprivation of particular nutrients in different diets," he explains via email.
While "dietary strategies emphasizing low-carbohydrate or low-fat intake may be effective in the short term for adults pursuing specific health goals," he says, it's important to consider how you'll replace the calories from carbs or fat with other macronutrients, how you're going to keep your calorie intake balanced and at the right amount, and the longer-term health consequences of your new diet.
"For adults considering a low-carbohydrate diet, be careful to avoid excessive increase in saturated-fat intake," because it may be lead to a higher risk of overall mortality, as well as mortality from cancer and cardiovascular disease, Tomey advises. "For adults considering a low-fat diet, be careful to avoid excessive increase in carbohydrate intake, and in particular refined grains and sugars."
"Beyond deciding to cut out a given nutrient, reflect on how to structure a meal plan for the day which is satiating, provides energy needs, ensures sufficient intake of lean protein, and achieves goals for calorie balance and weight management. A consultation with a nutritionist can be very helpful," he adds.
He also stresses that other factors can play a big role in people’s overall health, such as sleep patterns, weight, blood sugar, blood pressure and cholesterol.