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Jan 26, 2020

Quality Comes First in Carbs vs. Fats Debate

Healthy low-carbohydrate diet and healthy low-fat diet are linked to decreased mortality, study shows.

By CardioSmart News

Quality counts. And this may be especially true when it comes to what you eat.

When talking about diets these days, a lot of discussion seems to come down to carbohydrates vs. fats. Is eating fewer carbohydrates or less fat better for your health? To help shed light on this debate, a study recently published in JAMA Internal Medicine focused on how low-carbohydrate diets and low-fat diets are linked to deaths.

Study authors found that healthy low-carb diets and healthy low-fat diets were associated with decreased mortality. A healthy low-carb diet limited low-quality carbs—refined and added sugars—while incorporating more plant protein and unsaturated fat. A healthy low-fat diet had limited saturated fat and included plant protein and more high-quality carbs—whole grains, non-starchy vegetables, whole fruits.

"Our study extended the previous evidence and suggests that the health benefits of [a low-carbohydrate diet] or [low-fat diet] may depend not only on the types of protein and fat or carbohydrate but also on the quality of carbohydrate or fat remaining in the diet," the authors state.

In a similar way, unhealthy low-carb and unhealthy low-fat diets were linked to increased mortality. Low-carb and low-fat diets overall were not associated with total mortality, according to the study.  

Researchers examined information about the dietary intake of 37,233 adults (20 years old or older) reported to the U.S. National Health and Nutrition Examination Survey from 1999 to 2014. The average age of the group was 50, and more than half were women. When conducting the analysis, they adjusted for factors including age, sex, race or ethnicity, as well as educational level, family income, smoking, and family history of diabetes, heart disease or cancer.

What is at work with low-quality diets and mortality? The authors suggest that diets high in saturated fat lead to overeating and obesity. Saturated fats are tasty to many people but have a low-satiety effect. In terms of low-quality carbs, refined grains and added sugars have limited nutritional value but can lead to high blood sugar and insulin in the body after eating, and in turn this can cause inflammation, insulin resistance, and dyslipidemia.  

It’s important to note that the diets in this study don’t correspond to any specific popular diet. The study broke down a day’s worth of dietary intake in terms of percentage of energy from fat, protein and carbohydrates. Interestingly, a moderate low-carb diet still has about 40% of energy coming from carbs, and a low-fat diet still has about 30% energy from fat (20% for a very low-fat diet), according to authors.

Participants reported what they ate based on their memory, which could mean food intake was underreported or overreported. Another significant limitation: People were designated as eating a low-carb or low-fat diet based on an initial assessment. However, over time people may change the way they eat, so information about dietary intake may have been misclassified. Finally, as with other nutritional studies, this was based on observations, and therefore no conclusions about causes could be determined.

Low-fat diets have been recommended since the late 1970s to prevent chronic diseases. But recent research about the links between total fat intake and health outcomes have been inconsistent, the authors write. Meanwhile, low-carb diets have become a popular way to lose weight, but the long-term health effects of those diets remain unclear. This issue is more complex than looking just at fats or carbohydrates or proteins. More research is needed into the types of food as well as the quality of each component in a healthy diet.

This study strengthens the idea that the quality of food you eat matters to your overall health. Whatever eating pattern you follow, it’s a good idea to eat quality carbs and fats. That means avoiding refined carbohydrates, added sugars, and saturated fats. Instead, focus on whole grains, non-starchy vegetables, whole fruits, and unsaturated fats.


Read the full text: "Association of Low-Carbohydrate and Low-Fat Diets With Mortality Among U.S. Adults," Journal of the American Medical Association (JAMA) Internal Medicine, Jan. 21, 2020.


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