Low-carb diet emphasizing healthful plant-based foods linked to slower weight gain

Key takeaways:

• The quality of foods in low-carb diets play a crucial role in weight management, researchers said.
• Associations between diet quality and weight changes were stronger among participants with obesity.

A low-carbohydrate diet that emphasized high-quality protein, fat and carbohydrates from healthful plant-based sources was linked to less weight gain over a 4-year period, according to a recent study.

Meanwhile, a low-carbohydrate diet (LCD) high in animal protein and fat as well as refined carbohydrates was associated with faster weight gain, researchers reported.

“The key takeaway from our study is that not all LCDs are created equal when it comes to managing weight in the long term,” Binkai Liu, MS, a research assistant in the department of nutrition at Harvard T.H. Chan School of Public Health, told Healio. “The quality of food is crucial.”

Although previous clinical trials on LCDs have shown positive weight changes over short-term periods, how they impact weight in the long-term is uncertain, Liu and colleagues wrote in JAMA Network Open.

Furthermore, “few studies have considered the role of food group quality in the associations between LCDs and weight outcomes in free-living individuals with a range of carbohydrate intake typical for the general U.S. population,” they wrote.

The researchers examined the impact of five types of LCDs on 4-year weight changes using data from the Nurses’ Health Study, Nurses’ Health Study II and Health Professionals Follow-up Study.

The diets included:

• a total LCD (TLCD) centered around overall lower carbohydrate intake;
• an animal-based LCD (ALCD) centered around animal-sourced protein and fat;
• a vegetable-based LCD (VLCD) centered around plant-sourced protein and fat;
• a healthy LCD (HLCD) centered around less refined carbohydrates and more plant protein; and
• an unhealthy LCD (ULCD) centered around less healthy carbohydrates and more animal protein and unhealthy fat.

The overall cohort consisted of 123,332 (median age, 45 years; 83.8% women) participants.

Liu and colleagues found that, over the 4-year period, participants gained:

• 0.6 (95% CI, 0.04-0.08) kg per one standard deviation (SD) increase in TLCD score;
• 0.13 (95% CI, 0.11-0.14) kg per one SD increase in ALCD score;
• 0.39 (95% CI, 0.37-0.4) kg per one SD change in ULCD score.

“These findings align with existing evidence that excess consumption of red meats or processed animal products may lead to excess weight gain,” Liu said.

Meanwhile, one SD increase in VLCD score was associated with 0.03 kg (95% CI, 0.01-0.04) less weight gain, and one SD increase in HLCD score was associated with 0.36 kg (95% CI, 0.35-0.38) less weight gain.

Liu said the “clear differences in the impact of various LCDs on weight over time were surprising.”

“Notably, the contrast between the outcomes of the healthy plant-based low-carb diets and the less healthy ones was particularly compelling and highlights the importance of dietary quality in weight management strategies,” she said.

The study further showed that the associations were stronger among those with obesity. For example, individuals with a BMI greater than or equal to 30 kg/m² had 0.88 (95% CI, 0.8-0.97) kg less weight per one SD change in HLCD score.

According to Liu, more research is needed to better understand the association between LCDs, lean body mass and adiposity in a more diverse population. Still, the implications of the current study for public health and clinical practice “are significant,” she said.

"We found that following a healthy, plant-based, low-carb diet was associated with more favorable long-term weight management outcomes,” she said. “Therefore, opting for a diet rich in fresh fruits and nonstarchy vegetables, whole grains, nuts, legumes, olive oil, etc., is advisable for maintaining or improving overall health.”