A groundbreaking study from Harvard, published on December 27, 2023, in JAMA Network Open, challenges conventional wisdom on low-carb diets by highlighting the significance of food quality over sheer macronutrient quantity in sustaining weight loss.
Lead author Binkai Liu, PhD, a research assistant in the nutrition department at Harvard T.H. Chan School of Public Health, stresses the study’s pivotal finding: “Not all low-carbohydrate diets are created equal when it comes to managing weight in the long-term — the quality of the food is crucial.”
The research, spanning decades, delved into the impact of five different low-carb diet types on weight among participants. Dr. Liu emphasizes that low-carb diets rich in quality proteins, healthy fats, and a small portion of carbs from plant-based sources demonstrated slower weight gain. Conversely, low-carb diets high in animal proteins, fats, or refined carbs led to faster weight gain.
Renowned nutrition researcher Christopher Gardner, MD, not involved in the study, applauds its clarity on the oversimplified term “low-carb.” Gardner underscores that the study’s findings advocate for a plant-based, healthy approach as the most beneficial for long-term weight maintenance.
Decades-Long Observational Study on 120,000 Participants
While numerous studies have extolled the short-term benefits of low-carb diets, this Harvard study sought to fill a knowledge gap regarding their long-term efficacy and the impact of nutrient quality. Drawing data from the Nurses’ Health Studies and the Health Professionals Follow-Up Study, the research followed over 120,000 healthy adults from 1986 to 2018.
Participants provided self-reports of their diets and weights every four years via detailed surveys, resulting in a comprehensive dataset that underwent meticulous analysis.
Categories of Low-Carb Diets and Weight Impact
The study categorized low-carb diets into five types, all maintaining 30 to 40 percent carbohydrate intake:
Total Low-Carbohydrate Diet: Focused on overall lower carbohydrate intake.
Animal-Based Low-Carbohydrate Diet: Emphasizing animal-based proteins and fats.
Vegetable-Based Low-Carbohydrate Diet: Emphasizing plant-based proteins and fats, including sugar and refined white flour.
Healthy Low-Carbohydrate Diet: Emphasizing plant-based proteins, healthy fats, and fewer refined grains and added sugars.
Unhealthy Low-Carbohydrate Diet: Emphasizing animal-based proteins, unhealthy fats, and carbohydrates from processed sources.
Quality Matters: Healthy Low-Carb Diet Prevails
The study revealed that diets emphasizing plant-based proteins, healthy fats, and quality carbohydrates were associated with significantly slower long-term weight gain. In contrast, individuals adhering to unhealthy low-carb diets gained approximately 5.1 pounds over four years, while those following healthy low-carb diets lost roughly 4.9 pounds on average, marking a substantial 10-pound difference.
This association was most pronounced in participants under 55, overweight or obese, less physically active, or a combination of these factors.
Observational Nature and Complementary Findings
Although observational, the study’s unique strength lies in its extensive follow-up over 30 to 40 years. While it cannot establish causation, the findings complement existing randomized controlled trials (RCTs) emphasizing the importance of diet quality in addition to macronutrient composition.
Christopher Gardner, MD, coauthor of a recent RCT emphasizing diet quality, commends the study’s focus on long-term weight maintenance. He underscores that this aspect cannot be replicated in interventional RCTs and adds that the findings align with existing RCTs concluding that diet quality matters.
Expert Insights on a Healthy Low-Carb Diet
Registered Dietitian Julia Zumpano from Cleveland Clinic hails the study’s validation of the need to focus on diet quality. She emphasizes the importance of minimizing processed foods and prioritizing whole foods and lean protein sources from both plants and animals.
Zumpano recommends seeking guidance from a registered dietitian to develop a personalized plan for healthy low-carb living. Her suggested foods for a healthy low-carb diet include nonstarchy vegetables, protein sources like beans and lean animal proteins, and limited red meat, accompanied by small portions of whole grains and plant-based fats.
In a landscape where low-carb diets abound, this Harvard study reshapes the narrative by highlighting the paramount importance of choosing high-quality, plant-based options for sustained weight management.