Summary: In a small 12-month trial in adults with obesity, a ketogenic diet produced the largest sustained reductions in BMI, fat mass, fasting glucose, and cholesterol, while 16:8 time-restricted eating showed the most consistent rise in the appetite-regulating peptide orexin-A; the orexin-A findings are exploratory.
PICO Summary
| Element | Detail |
|---|---|
| Population | 30 adults with obesity (BMI ≥30), about 10 per arm; 12-month three-arm randomised controlled trial, Italy. |
| Intervention | Hypocaloric ketogenic diet for 12 months. |
| Comparison | 16:8 time-restricted eating, or 5:2 alternate-day fasting. |
| Outcome | The ketogenic diet gave the largest sustained reductions in BMI, fat mass, fasting glucose, and total cholesterol. Time-restricted 16:8 eating produced faster early metabolic improvement and the most consistent longitudinal rise in orexin-A. All groups improved metabolic flexibility and inflammation. Orexin-A increases correlated with these effects, but mediation analyses were exploratory and non-causal. Between-group differences in fat mass, glucose, and orexin-A trajectories survived correction for multiple comparisons. |
Expert Commentary
This is a small mechanistic trial with an interesting neuroendocrine angle, and its size demands that it be read as hypothesis-generating rather than definitive. The headline metabolic comparison is plausible and consistent with other work, with the ketogenic diet delivering the largest sustained anthropometric and glycaemic improvements while time-restricted eating produced quicker early gains, useful texture for tailoring dietary advice. The novel element is orexin-A, a peptide involved in energy regulation, which rose most consistently with 16:8 eating and correlated with improved metabolic flexibility and lower inflammation. I would stress what the authors themselves stress: with only about ten participants per arm, the correlations are exploratory and explicitly non-causal, so orexin-A should be treated as a candidate biomarker of dietary response, not an established mechanism or target. A 12-month duration is a genuine strength for adherence and durability, but it cannot offset the small sample for confident between-diet claims. Can I use this with my patients? Only loosely. It modestly reinforces that both ketogenic and time-restricted approaches can work and that the best diet is often the sustainable one, while the orexin-A story is intriguing background that needs much larger trials before it informs how I counsel patients.
References
Monda A, Casillo M, Allocca S, et al. Metabolic and orexin-A responses to ketogenic diet and intermittent fasting: a 12-month randomized trial in adults with obesity. Nutrients. 2026;18(2):238. doi:10.3390/nu18020238