Does Quality Matter with Low Carb Diets?

Researchers from Harvard’s Chan School of Public Health recently published an analysis of the association between low carbohydrate diets (LCDs) and long-term weight control, with a special focus on diet quality. The analysis included 3 well-described prospective cohorts, the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHSII), and the Health Professionals Follow-up Study (HPFS), with over 123,000 total participants with a mean age of 45. The primary outcome of interest was self-reported weight change over 4-year periods, and how this related to 5 indices of LCDs, including total carbohydrate intake, but also indices related to the proportion of diets comprised of plant versus animal protein and fat, as well as refined compared to more healthful carbohydrates.

The overall carbohydrate intake was higher in these cohorts than in previously published randomized trials. For example, the percent of calories from carbohydrates in these (pooled) cohorts was approximately 40% in the 5th quintile (and 58% in the 1st quintile), compared to 34% at the end of a 1-year trial which had demonstrated superior weight loss when compared to a low-fat diet. However, it may more closely resemble the real-world ability to maintain a low-carbohydrate diet over a longer period.

Overall, a U-shaped curve between total carbohydrate intake and weight change was observed over 4-year periods. However, the focus on diet quality indicated that LCDs that emphasized healthy plant-based foods were linked to less weight gain. In contrast, LCDs that emphasized animal-based proteins and fats, as well as those with a higher proportion of refined carbohydrates, were associated with more weight gain. While not a randomized trial, this analysis suggests that a focus on macronutrients alone may not be enough to maximize weight loss, particularly over a longer period of time, but that diet quality is an important component of healthy weight control.