Study Answers if a Low-Carb Diet or Low-Fat Diet Helps You Live Longer

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  • New research determines whether a low-carb or low-fat diet is better for longevity.

  • Researchers found that participants who followed one diet had an 18% lower mortality rate than those that followed the other.

  • Experts interpret the findings.

When it comes to diets, every kind of eating plan boasts different benefits, whether it’s weight loss, reducing inflammation, or boosting your brain power. Now, new research finds out if a low-carb diet or a low-fat diet promotes longevity.

The study published in the Journal of Internal Medicine looked at the effects of both low-carbohydrate diets and low-fat diets to determine which of the two helped people live a longer life—and the results may surprise you.

Researchers analyzed data from the NIH-AARP Diet and Health Study, which in 1995 and 1996 recruited AARP members ages 50 to 71. Study participants were asked to complete a food questionnaire. Participants who reported having cancer, heart disease, stroke, diabetes, end-stage kidney disease, or other health issues were excluded from the analysis—which left 371,159 participants in total.

The participants’ food choices were categorized 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, like whole grains, whole fruit, legumes, and non-starchy vegetables, and limited saturated fat.

After following up around 23.5 years later, researchers found that participants whose eating patterns were most similar to 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. On the other hand, participants whose eating patterns were most similar to the healthy low-carb diet had only a slightly lower mortality rate compared to those with eating patterns that least resembled this diet.

What is a low-carb diet?

A low-carb diet typically limits how many carbohydrates you eat in a day favoring more protein-rich or fat-rich foods on the plate, says Melissa Prest, D.C.N., R.D.N., national media spokesperson for the Academy of Nutrition and Dietetics and member of the Prevention Medical Review Board. “A low-carb diet may be considered a diet where total carbohydrate intake is less than 45% of total calories,” adds Keri Gans, M.S., R.D., author of The Small Change Diet.

What is a low-fat diet?

A low-fat diet may be considered a diet where total fat intake is less than 30% of total calories, says Gans. However, she notes that these percentages may vary depending on the specific diet protocol you are following. “A low-fat diet limits how many fat-rich foods one eats with a higher proportion of carbohydrate and protein foods on the plate,” explains Prest.

Why is a low-fat diet better for longevity than a low-carb diet?

In this study, researchers noted that those who ate a lower-fat diet and swapped out saturated fats lived longer than those who ate a low-carb diet. This may be due to more plant foods on the plate which other studies have found to be important for preventing heart disease and certain cancers, says Prest.

Still, Gans notes, a lot has to do with the food choices within each diet and what foods may actually be omitted or included. “For instance, high-fiber carbohydrates, such as oats, beans, and 100% whole grains have been linked with many health benefits, such as decreasing cholesterol levels, preventing risk for heart disease, and positive correlation with digestive health. If a person is to lower their intake of these types of foods, they miss out on the health benefits.” On the other hand, saturated fat is linked to an increase in heart disease and limiting foods, such as red meat, butter, heavy cream, and fried foods, may come with a benefit, she adds.

The bottom line

While there are limitations to this study, i.e. only measuring diet intake once, it highlights that a more balanced plate rather than severely minimizing carbohydrates reduces the risk of heart disease and contributes to longevity, says Prest. “Research has shown that dietary patterns that are rich in plant foods, lower in saturated fats, and include whole grains are strongly associated with less chronic inflammation, lower rates of heart disease and certain cancers, and are commonly consumed in people who live the longest.”

At the end of the day, it is the food choices that matter and not what you label your diet, as not all fats or carbs are created equal, says Gans. “Also, keep in mind, diet is only a part of living a healthy lifestyle—getting adequate sleep, being physically active, and reducing stress is also very important.”

The most important conclusion is that a “healthy” diet (whether it was low carbohydrate or low fat) was associated with substantial health benefits and prolongation of life, says Brett Victor, M.D., a cardiologist from Cardiology Consultants of Philadelphia. “The important takeaway here is to talk to your health professional or a registered dietitian if you want to be making the best decisions for your health and longevity, rather than following the latest internet fad diet.”

Overall, choosing more complex carbohydrates (whole grains, whole fruits, legumes, and non-starchy vegetables) as opposed to low-quality carbohydrates (refined grains, added sugar, fruit juice, and starchy vegetables) will result in a longer and healthier life, adds Dr. Victor. The same goes for increasing plant-based vs animal protein and decreasing saturated fat in one’s diet.

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