TOPLINE

Women with obesity who completed a very low-calorie ketogenic diet (VLCKD) for 1 month maintained clinically meaningful weight loss over 12 months, driven predominantly by fat mass reduction. The initial metabolic adaptation, characterized by reduced energy expenditure during the ketogenic phase, was reversed and not sustained at 6 or 12 months.

METHODOLOGY

• A VLCKD is an effective weight-loss strategy that may better preserve lean body mass. However, prior studies have reported a marked decline in 24-hour energy expenditure (24hEE) and sleeping metabolic rate (24hSMR) after 1 month — highlighting the need to examine how body composition and energy metabolism change once the VLCKD phase ends.
• Researchers conducted a prospective follow-up study of 17 adult women with obesity (BMI > 30) who completed a 1-month VLCKD (700-800 kcal/d; 11% carbohydrate, 46% fat, and 43% protein).
• After completing the VLCKD, participants underwent a 4-week structured dietary reintroduction phase with progressive carbohydrate increases (energy intake rising from 800 to 1400 kcal/d), followed by a hypocaloric Mediterranean diet (30% fat, 45% carbohydrate, and 25% protein) at about 25 kcal/kg of ideal body weight.
• Body composition (measured by DEXA) and 24hEE (measured using whole-room indirect calorimetry) were assessed at baseline, after 1 month of VLCKD, and at 6 and 12 months of follow-up; changes in body weight, fat mass, lean soft tissue, 24hEE, 24hSMR, and respiratory exchange ratio (RER) were evaluated.
• Metabolic adaptation was assessed by comparing observed 24hSMR with predicted values derived from an independent cohort of 22 healthy women.

TAKEAWAY

• Fourteen participants returned for the 6-month follow-up and 11 for the 12-month follow-up; after the initial 7% weight loss during VLCKD, body weight dropped by an additional 3.9% at 6 months (P < .05), primarily driven by a 10% reduction in fat mass (P < .05); at the 12-month follow-up, three participants lost additional weight, while the others remained stable or partially regained weight.
• Between the end of VLCKD and the 12-month follow-up, both 24hEE and 24hSMR trended upward, though these increases were not statistically significant. Minute-by-minute analysis showed a significant rise in EE at 6 months compared with the end of VLCKD, with a nighttime-specific increase of 0.239 kcal/min.
• The metabolic adaptation seen after 1 month of VLCKD, characterized by an observed 24hSMR being significantly lower than predicted (mean difference, -108 kcal/d; P = .022), was no longer detectable at 6 or 12 months.
• RER increased markedly from the end of VLCKD to 6 months and remained elevated at 12 months, driven by increased carbohydrate oxidation and reduced fat oxidation (P < .001 for all).

IN PRACTICE

“The present study provides novel insight into the time course of metabolic adaptation following VLCKD, demonstrating that the early reduction in energy expenditure is not sustained after dietary reintroduction. These findings have important implications for understanding the physiological determinants of weight-loss maintenance and support the beneficial role of VLCKD in the control of body weight when implemented within a structured follow-up program,” the authors of the study wrote.

SOURCE

The study was led by Alessio Basolo, Obesity and Lipodystrophy Center, University Hospital of Pisa, Pisa, Italy. It was published online in Obesity.

LIMITATIONS

The study had a small sample size, and some participants did not finish the 12‑month follow-up. It consisted only of women with obesity, and some degree of clinical heterogeneity was present, limiting the generalizability of the findings to broader populations. Moreover, there was no comparison group on a nonketogenic low-calorie diet.

DISCLOSURES

The study was supported by the University Hospital of Pisa. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.