JAMA Network Open · 6 authors, 4 centres
This summary was generated by AI from a single paper. It has not been reviewed by a clinician and is not clinical advice. Verify against the source before acting on it.
This large cohort study found that the quality of macronutrients in low-carbohydrate diets (LCDs) is critical for long-term weight management. A healthy LCD emphasizing plant-based proteins, healthy fats, and whole grains was associated with slower weight gain, while an unhealthy LCD focused on animal proteins and refined carbohydrates was linked to faster weight gain. These findings highlight that diet quality, not just carbohydrate quantity, is key for weight control.
**Background:** Low-carbohydrate diets (LCDs) are popular for weight loss, but long-term effects and the role of macronutrient quality are unclear. This study aimed to assess associations between changes in five LCD indices—differing in macronutrient source and quality—and 4-year weight change in three large US cohorts.
**Methods:** Data were from the Nurses’ Health Study (NHS, 1986-2010), NHSII (1991-2015), and Health Professionals Follow-up Study (HPFS, 1986-2018), including 123,332 participants (mean age 45.0 years, 83.8% female). Diet was assessed every 4 years via validated food frequency questionnaires. Five LCD scores (0-30) were derived: total LCD (TLCD), animal-based LCD (ALCD), vegetable-based LCD (VLCD), healthy LCD (HLCD, emphasizing plant protein, healthy fats, and less refined carbs), and unhealthy LCD (ULCD, emphasizing animal protein, unhealthy fats, and refined carbs). The primary exposure was 4-year change in each score, categorized into quintiles (Q1=largest decrease, Q3=no change, Q5=largest increase). The outcome was 4-year weight change. Multivariable generalized linear regression models adjusted for age, race, family history, baseline BMI, smoking, physical activity, alcohol, and other confounders.
**Key Results:** Over 4-year intervals, participants gained a mean of 1.3 kg. Compared with stable adherence (Q3), the largest increase in HLCD (Q5) was associated with 0.64 kg less weight gain (95% CI, 0.60 to 0.69 kg), while the largest decrease (Q1) was associated with 0.32 kg more weight gain (95% CI, 0.28 to 0.37 kg). Conversely, the largest increase in ULCD (Q5) was associated with 0.42 kg more weight gain (95% CI, 0.38 to 0.47 kg), and the largest decrease (Q1) with 0.60 kg less weight gain (95% CI, 0.55 to 0.65 kg). Per 1-SD increase, HLCD was associated with -0.36 kg (95% CI, -0.38 to -0.35 kg) and ULCD with +0.39 kg (95% CI, 0.37 to 0.40 kg). ALCD was associated with more weight gain (+0.13 kg per 1-SD, 95% CI 0.11 to 0.14 kg), while VLCD showed modest benefit (-0.03 kg per 1-SD, 95% CI -0.04 to -0.01 kg). TLCD showed no significant association (0.06 kg per 1-SD, 95% CI 0.04 to 0.08 kg). Nonlinear associations were observed (P for curvature <0.001 for all). Stratified analyses revealed stronger effects among younger (<55 years), less active, and overweight/obese individuals. For example, among those with BMI ≥30, Q5 of HLCD was associated with 1.63 kg less weight gain (95% CI, 1.40 to 1.86 kg), while Q5 of ULCD was associated with 0.67 kg more weight gain (95% CI, 0.44 to 0.90 kg).
**Clinical Implications:** This study demonstrates that the quality of macronutrients in LCDs is a critical determinant of long-term weight change. A healthy LCD rich in plant-based proteins, unsaturated fats, and whole grains is associated with slower weight gain, whereas an unhealthy LCD high in animal proteins, saturated fats, and refined carbohydrates is linked to faster weight gain. These findings argue against a sole focus on carbohydrate quantity and emphasize the importance of nutrient quality for weight management. Clinicians should guide patients toward high-quality LCD patterns, particularly those who are younger, less active, or have higher BMI, as they may derive greater benefit.