Long-Term Weight Loss: Harvard Reveals the Diet That Truly Works

Long-term weight management isn’t just about cutting calories—it’s about choosing the right types of foods. A Harvard study highlights that not all low-carb diets are equally effective. Diets focusing on plant-based proteins and fats, along with “healthy” carbohydrates, show the best results for preventing weight gain over the years.

The Study

Led by Binkai Liu at Harvard T.H. Chan School of Public Health, researchers analyzed data from 123,332 healthy adults between 1986 and 2018. Data came from three major U.S. epidemiological studies: the Nurses’ Health Study I & II and the Health Professionals Follow-up Study. Participants reported their diet and weight every four years. The study compared five types of low-carb diets, differentiated by protein and fat sources (animal vs. plant), to assess long-term effects on weight gain.

Greater Effectiveness in Adults Under 55

The benefits of plant-based low-carb diets were especially noticeable in adults under 55, particularly those overweight or obese. Lower levels of physical activity further amplified the differences between diet types.

Foods to Prioritize for Effective Weight Loss

Published in JAMA Network Open, the study concludes that diets rich in plant-based proteins and fats—like legumes, whole grains, vegetables, fruits, and vegetable oils—combined with unrefined carbohydrates, are most effective for long-term weight management. Diets high in animal proteins and fats were associated with greater weight gain.

Recommended foods for a healthy low-carb diet include:

• Legumes: lentils, chickpeas, beans, fava beans

• Whole grains: quinoa, brown rice, whole-grain bread

• Fresh fruits and vegetables: high in fiber and antioxidants

• Soy products: tofu, tempeh

• Vegetable oils: olive, rapeseed, walnut

• Nuts: almonds, walnuts, hazelnuts

• Low-fat dairy

These align with France’s National Nutrition Health Program (PNNS), which emphasizes natural foods and regular physical activity.

Caution and Limitations

While results are promising, the study notes some limitations. Only participants in the Nurses’ Health Study II showed a significant decrease in weight gain with plant-based proteins. Further research is needed to refine conclusions.

Key takeaway: Not all low-carb diets are equal. Promoting whole grains, fruits, and vegetables should remain a public health priority.

Conclusion

For sustainable long-term weight management, focus on plant-based proteins and fats and healthy carbohydrates rather than eliminating entire food groups. A balanced, nutrient-rich diet combined with lifestyle choices like regular activity ensures healthier outcomes and reduces long-term weight gain.

References

• ETX Studio, Harvard T.H. Chan School of Public Health

• JAMA Network Open, Liu B. et al., 2025