This prospective, single-center, crossover study aims to evaluate the metabolic and hormonal effects of a ketogenic diet compared to a Mediterranean diet in patients with active acromegaly. Twenty-six adult patients with biochemically confirmed active acromegaly will undergo a three-week ketogenic diet followed by a three-week Mediterranean diet, with a two-week transitional phase. The primary outcome is the change in serum IGF-1 levels. Secondary outcomes include changes in anthropometric, biochemical, and inflammatory parameters. The study also explores the feasibility and safety of a structured ketogenic dietary intervention in this population.

Acromegaly is a rare endocrine disorder characterized by excessive secretion of growth hormone (GH) and insulin-like growth factor 1 (IGF-1), often leading to metabolic complications including insulin resistance, diabetes mellitus, and hepatic steatosis. Nutritional status is a key regulator of the somatotropic axis, and recent evidence suggests that specific dietary patterns can modulate GH and IGF-1 secretion. The ketogenic diet (KD), characterized by high fat, moderate protein, and very low carbohydrate intake, induces nutritional ketosis, improves insulin sensitivity, and reduces circulating insulin levels. These effects may influence the hepatic expression of GH receptors and IGF-1 production. Preliminary data suggest that KD may reduce IGF-1 levels in patients with acromegaly.

This study is designed as a single-arm crossover trial involving 26 patients with active acromegaly. All participants will follow a structured ketogenic diet for three weeks (~1200 kcal/day, carbohydrates <30 g/day), followed by a two-week transition phase, and then a Mediterranean diet for three weeks (~1200 kcal/day, plant-based, rich in olive oil and fish). Baseline, post-KD, and post-Mediterranean assessments will include serum IGF-1 and GH levels, anthropometric measurements, body composition (via bioelectrical impedance analysis), liver enzymes, lipid profile, insulin resistance indices (HOMA-IR), and inflammatory markers (c-reactive protein, neutrophil to lymphocyte ratio, platelet to lymphocyte ratio).

The primary endpoint is the within-subject change in serum IGF-1 concentration. Secondary endpoints include changes in metabolic and inflammatory markers. Antidiabetic medications will be temporarily discontinued during the ketogenic phase under clinical supervision in patients not requiring insulin. The study is expected to provide novel insights into the impact of dietary modulation on the somatotropic axis in acromegaly and may inform future integrative therapeutic strategies.

Inclusion Criteria:

• Age ≥ 18 years
• Confirmed diagnosis of active acromegaly (elevated IGF-1, GH non-suppressible at OGTT)
• Stable medical therapy for ≥ 3 months
• BMI 25-40 kg/m²
• Informed consent signed

Exclusion Criteria:

• Type 1 diabetes or insulin-treated type 2 diabetes mellitus
• History of ketoacidosis
• Active malignancy, decompensated liver/kidney disease
• Severe psychiatric disorders or eating disorders
• Pregnancy or breastfeeding

Individual participant data (IPD) will not be shared. This decision is based on institutional policy and ethical considerations, as the study involves a relatively small and identifiable patient population with a rare endocrine disorder. Data sharing may compromise patient confidentiality despite de-identification procedures.