Dr. Shan

When It Comes to Healthy Dieting, It’s the Quality of Nutrients That Counts

MedicalResearch.com Interview with:

Dr. Shan

Dr. Shan

Zhilei Shan PhD
Postdoctoral fellow on Nutritional Epidemiology
Harvard T.H. Chan School of Public Health

MedicalResearch.com: What is the background for this study?

Response: Long-standing controversies have focused on the health consequences of dietary fat and carbohydrate. Previous evidence has shown that different types of carbohydrates and fats have varying effects on disease risk and health. For example, carbohydrates from refined grains and added sugars may contribute to insulin resistance and other metabolic problems while carbohydrates from whole grains and whole fruits appear to be beneficial. Likewise, replacing saturated fat with unsaturated fat was associated with lower risk of heart disease and mortality.

Therefore, it is crucial to incorporate quality and types of carbohydrate and fat when investigating the associations of low-fat and low-carbohydrate diets with mortality.

MedicalResearch.com: What are the main findings?

Response: Our study used data of 37,233 adults ages 20 or older participating in the U.S. National Health and Nutrition Examination Survey from 1999 to 2014. When only considering the quantity of macronutrients, the overall low-carbohydrate or low-fat diets showed no significant impact on mortality. When we incorporated the quality and food sources of the carbohydrates, protein, and fats consumed, a healthy low-carbohydrate diet (lower amounts of low-quality carbohydrates, higher amounts of plant protein and unsaturated fat) and a healthy low-fat diet (lower amounts of saturated fat, higher amounts of high-quality carbohydrates and plant protein) were associated with lower total mortality.

On the contrary, people who ate unhealthy low-carbohydrate or low-fat diets (high amounts of low-quality carbohydrates, animal protein, and saturated fat) had a higher risk of premature death.

MedicalResearch.com: What should readers take away from your report?

Response: The debate on the health consequences of low-fat or low-carbohydrate diets is largely moot unless the food sources of fats or carbohydrates are clearly defined. A healthy diet should contain relatively high amounts of healthy food sources of macronutrients, such as whole grains, non-starchy vegetables, whole fruits, and nuts, but low amounts of refined grain, red meat and processed meat, and added sugar.

MedicalResearch.com: What recommendations do you have for future research as a result of this work?

Response: Our findings show clearly that the quality rather than the quantity of macronutrients in our diet has an important impact on our health. Future research on macronutrients should also take the quality and food sources into account. 

MedicalResearch.com: Is there anything else you would like to add?

Response: Several limitations of our study should be noted. The dietary scores in this study were not designed to mimic any particular versions of diets, so the results could not be directly translated to the assessment of health benefit or risk associated with the popular versions of the diets. The dietary information was based on a single assessment at baseline and participants may change their diets during the follow-up. Additionally, we could not determine any causality.

Any disclosures? None.


Shan Z, Guo Y, Hu FB, Liu L, Qi Q. Association of Low-Carbohydrate and Low-Fat Diets With Mortality Among US Adults. JAMA Intern Med. Published online January 21, 2020. doi:10.1001/jamainternmed.2019.6980


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Last Updated on January 22, 2020 by Marie Benz MD FAAD