A randomized controlled trial comparing a very low-calorie low-fat ketogenic diet with a standard hypocaloric diet in adults with class I obesity

Background

The global rise in obesity, driven by hypercaloric diets and sedentary lifestyles, has intensified interest in novel dietary interventions. Very low-calorie ketogenic diets (VLCKDs) induce rapid weight loss but are typically high in fat. This study assessed the efficacy and safety of a very low-calorie, low-fat, ketogenic diet (VLCLFKD), also known as the Zélé method, versus a standard low-calorie diet (LCD) in adults with class I obesity.

Methods

In this 12-week, randomized, double-blind controlled trial (NCT06275347), 88 participants were allocated to VLCLFKD (n = 56) or LCD (n = 32), with 77 completing the protocol. The primary endpoint was weight change; secondary outcomes included body composition, fasting glucose, lipid profile, blood pressure, hepatic and renal function, and acid–base balance. All participants received weekly clinical and dietary support.

Results

VLCLFKD led to significantly greater weight loss (−12.4 ± 2.8 kg) than LCD (−7.0 ± 1.9 kg; p < 0.001). Fat mass reduction accounted for 82.1 % of total weight loss in the VLCLFKD group, compared to 38.4 % in the LCD group (p < 0.001), with markedly lower lean mass loss (11.9 % vs. 51.0 %). Significant improvements were observed in fasting glucose (−12.8 mg/dL), total cholesterol (−37.4 mg/dL), triglycerides (−67.4 mg/dL), and blood pressure normalization (88.1 % vs. 71.4 %). Renal and hepatic function and acid–base balance remained stable. No serious adverse events occurred.

Conclusion

The VLCLFKD (Zélé method) is a safe, fat-targeted, and metabolically advantageous strategy for class I obesity, delivering superior weight and metabolic outcomes compared with a conventional LCD while preserving lean mass.