Scientific synthesis · Compiled by Brian Gaillard
Brian Gaillard
Hybrid athlete and applied nutrition enthusiast at Nutrition•pro
The diet market generates a constant stream of contradictory promises: keto, Mediterranean, intermittent fasting, Dukan, low-carb. This synthesis brings together 12 major meta-analyses published between 2013 and 2024 in the BMJ, JAMA, NEJM, Cochrane, and The Lancet, to answer a single question: which diets actually hold up when you cross-reference data from over 300 randomized trials and 130,000 participants?
Our approach
Executive summary
The key figures emerging from the 12 compiled meta-analyses.
At 6 months, most restrictive diets produce a weight loss of 4 to 7 kg, with a robust signal across all sources (Ge 2020, Johnston 2014, Mansoor 2016, Bueno 2013). At 12 months, the difference between diets largely disappears (Patikorn 2021, Naude 2022). Adherence then becomes the determining factor : only the Mediterranean (PREDIMED, Schwingshackl 2018) and DASH (Soltani 2016) maintain their cardiovascular benefits beyond 24 months.
1. Weight loss at 6 months: restrictive diets dominate
In the short term, diets that restrict the most (low-carb, ketogenic, high-protein) produce the fastest weight loss. The logic is mechanical: the sharper the restriction, the greater the average caloric deficit.
2. At 12 months: the differences collapse (and some weight is regained)
Cross-reference of 4 independent meta-analyses (Ge 2020, Johnston 2014, Mansoor 2016, Tobias 2015). Key point to note when reading the figures: Weight loss at 12 months is not the loss at 6 months continuing; it is the loss that remains after partial weight regain between 6 and 12 months. This is a nearly universal phenomenon in long-term studies: after the peak at 4-6 months, metabolic adaptation (decrease in resting energy expenditure), fatigue from restriction, and gradual return to old habits cause weight to rebound.
Concrete result: average weight loss across all categories stands at around 2.5 to 3.5 kg at 12 months, compared to 4 to 7 kg at 6 months. In other words, on average 30 to 45% of the weight lost is regained in the second half of the year. And this regain is not the same across all diets.
3. Effect on cardiometabolic markers
Beyond weight loss, this is where diets truly differentiate themselves. LDL cholesterol and HbA1c tell two opposite stories.
4. Adherence: the true decisive factor
No diet works if it isn't followed. 12-month dropout rates are probably the most predictive variable of actual outcomes.
The strictest diets shine at 6 months then collapse at 12 months due to dropouts. The Mediterranean diet, less dramatic initially, gains ground long-term because people stick with it. The best diet is the one you continue to follow.
5. Key takeaway: diets that stick
The composite score (12-month weight loss × metabolic markers × adherence × level of evidence) yields a stable ranking across meta-analyses.
6. How to choose in practice
The "ideal" diet doesn't exist in absolute terms, but three profiles recur in the literature:
Goal: cardiovascular health or sustainable weight loss. Mediterranean or DASH. Demonstrated cardiovascular benefits at 2 to 5 years, high adherence, moderate cost.
Goal: glycemic control (type 2 diabetes or prediabetes). Moderate low-carb or Mediterranean. Both are validated (Naude 2022, Estruch 2018), with an advantage for low-carb on short-term HbA1c.
Goal: rapid weight loss over 3 months maximum. Moderate high-protein or moderate low-carb, with transition to Mediterranean in the maintenance phase to prevent regain.
Methodology
This synthesis is an umbrella review (synthesis of existing meta-analyses). 12 major meta-analyses published in peer-reviewed journals (BMJ, JAMA, NEJM, The Lancet, Cochrane) were aggregated. The values presented are weighted averages calculated from the effect estimates of each meta-analysis, weighted by pooled sample size.
Inclusion criteria for retained meta-analyses: publication in a PubMed-indexed journal with impact factor greater than 3, at least 5 randomized controlled trials, follow-up duration ≥ 6 months for short-term analyses and ≥ 12 months for long-term analyses, adult population overweight or in good health, PRISMA method or equivalent.
The final composite score integrates 4 weighted dimensions: weight loss efficacy at 12 months (40%), effect on metabolic markers (25%), adherence at 12 months (25%), GRADE level of evidence (10%).
- Ge L et al. (2020). Comparison of dietary macronutrient patterns of 14 popular named dietary programmes for weight and cardiovascular risk factor reduction in adults. BMJ, 369:m696.
- Johnston BC et al. (2014). Comparison of weight loss among named diet programs in overweight and obese adults. JAMA, 312(9):923-933.
- Mansoor N et al. (2016). Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors. British Journal of Nutrition, 115(3):466-479.
- Bueno NB et al. (2013). Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss. British Journal of Nutrition, 110(7):1178-1187.
- Patikorn C et al. (2021). Intermittent Fasting and Obesity-Related Health Outcomes. JAMA Network Open, 4(12):e2139558.
- Allaf M et al. (2021). Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database Syst Rev, 1(1):CD013496.
- Estruch R et al. (2018). Primary Prevention of Cardiovascular Disease with a Mediterranean Diet (PREDIMED). New England Journal of Medicine, 378:e34.
- Schwingshackl L et al. (2018). Comparative Effects of Different Dietary Approaches on Blood Pressure. Advances in Nutrition, 9(2):76-103.
- Soltani S et al. (2016). The effect of the DASH diet on weight and body composition. Nutrition Journal, 15:101.
- Naude CE et al. (2022). Low-carbohydrate versus balanced-carbohydrate diets. Cochrane Database Syst Rev, 1(1):CD013334.
- Tobias DK et al. (2015). Effect of low-fat diet interventions on long-term weight change. The Lancet Diabetes & Endocrinology, 3(12):968-979.
- Viguiliouk E et al. (2019). Effect of vegetarian dietary patterns on cardiometabolic risk factors in diabetes. Clinical Nutrition, 38(3):1133-1145.
Brian Gaillard
Author Nutrition and Performance
Hybrid athlete for over 10 years: strength training, running, swimming, HIIT and muay thai. Brian selects, compiles and contextualizes recent scientific literature on sports nutrition and weight loss for Nutrition•pro's editorial content. Each synthesis is based on meta-analyses and clinical trials filtered according to their level of evidence, combined with experience accumulated through his training and exchanges with coaches and nutritionists.
