Counting Quality, Not Carbs, May Be Key to Weight Management

The key to maintaining a low-carbohydrate diet without gaining weight over the long term may be the quality of protein, fat, and carbohydrates consumed, according to an analysis of three ongoing studies of female nurses and male health professionals.

Compared with people who ate primarily animal-sourced proteins and fats or refined carbohydrates, those who relied on high-quality macronutrients from plant-based sources saw slower weight gain over a 4-year period.

“This was an observational study and participants were not on any specific diet,” said Binkai Liu, MS (Harvard T.H. Chan School of Public Health, Boston, MA), the study’s lead author.

“What it is demonstrating is that eating a low carb diet in general may or may not be a benefit in your weight management, but focusing on the macronutrients, the foods that you are choosing within the diet, is more important than the quantity of the carbs,” she added.

The study, published last week in JAMA Network Open, is consistent with several other studies, including the PREDIMED trial, which concluded that a low-carb Mediterranean-style diet emphasizing extra-virgin olive oil, fruits, vegetables, whole grains, and legumes is not only better for weight control than a low-carb, low-fat diet, but also may increase the function of HDL cholesterol in people at high risk for CVD.

Liu and colleagues examined data from the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study, which enrolled initially healthy participants in the 1970s and 1980s. Diet was assessed every 4 years with a food frequency questionnaire, and participants self-reported their weight.

Focusing on the macronutrients, the foods that you are choosing within the diet, is more important than the quantity of the carbs. Binkai Liu

Among the 123,332 participants (mean age 45 years; 83.8% female), the median daily carbohydrate intake as a percentage of calories, ranged from 38.3% to 40.9%. Those most adherent to a low-carb diet at baseline were often current smokers, and had lower physical activity levels, lower daily calorie intake, higher BMI, and a family history of diabetes compared with those who were less adherent to low-carb diets.

Scoring Healthy

The investigators categorized participants into five low-carb groups: total low-carb diet (TLCD) emphasizing overall lower carbohydrate intake; animal-based (ALCD) further emphasizing animal sources of protein and fat; vegetable-based (VLCD) further emphasizing plant sources of protein and fat; healthy (HLCD) with less refined carbohydrates, more plant protein, and healthy fat; and unhealthy (ULCD) with less carbohydrates from healthful sources, such as whole grains, more animal protein, and unhealthy fat.

Scores were calculated based on consumption of carbohydrates, fat, and protein, which were ranked into 11 categories based on their percentage contributions to total energy intake. High-quality carbohydrates included fruit carbohydrate excluding juice sugar, vegetable carbohydrate excluding potato, and sum of carbohydrate from whole grains. Low-quality carbohydrates included sum of carbohydrate from potato, added sugar in foods, and refined grains.

A total quality score was calculated for each diet group using this algorithm, which deviations based on the protein source, and the baseline scores were compared with those over the 4-year period.

The mean weight gain ranged from 0.8 kg to 1.8 kg.

Among the five low-carb groups, each 1-SD quality increase in score over 4 years was associated with 0.06 kg weight gain in the TLCD group, 0.13 kg weight gain in the ALCD group, and 0.39 kg weight gain in the ULCD group. Conversely, each 1-SD increase in score was associated with 0.03 kg less weight gain in the VLCD group and 0.36 kg less weight gain in the HLCD group.

The researchers say the findings highlight the importance of incorporating healthier food groups into low-carb eating as an effective approach for weight management.

The study does have its limitations, however. In addition to being predominately female health professionals, it is limited in that participants were primarily white, Liu noted. “We hope future research can look into a more diverse demographic and replicate these results,” she told TCTMD.