Legume Consumption Within a Mediterranean Diet Framework and Its Effects on Cellular Hydration, Autonomic Regulation, and Functional Performance in Competitive Swimmers: A Five-Month Intervention Study

This interventional study was conducted in competitive swimmers to evaluate the impact of higher legume consumption, within a Mediterranean diet framework, on markers of cellular health, body water distribution, autonomic regulation, and functional performance. Thirty-nine competitive swimmers (mean age approximately 20 years; both males and females) were enrolled and followed for five months during the first half of the competitive season. All athletes trained under similar standardized conditions, completing six weekly sessions that combined dry-land pre-activation, in-water training, and, in some sessions, gym-based strength work.

At baseline, participants completed an online dietary assessment using the validated MEDI-LITE questionnaire to quantify adherence to the Mediterranean diet and habitual legume intake. Based on baseline legume consumption, swimmers were assigned to one of three groups: a control group (<1 serving/week, no change in diet), a moderate-intake group (≈2 servings/week increased to 3 servings/week), and a high-intake group (≈3-4 servings/week increased to 6 servings/week). A qualified nutrition professional provided counseling to adjust only legume intake, while other aspects of diet were kept stable. Dietary adherence and legume consumption were monitored regularly throughout the study, and the MEDI-LITE questionnaire was repeated at the end of the intervention.

The primary endpoints are phase angle and hydration indices derived from bioelectrical impedance analysis, including extracellular water (ECW), intracellular water (ICW), and the ECW/ICW ratio, which are considered integrated markers of cellular integrity, cell mass, and fluid compartmentalization. Secondary endpoints include measures of autonomic function-heart rate variability and cardiac coherence-assessed with a standardized device, and a critical swim speed test performed in an indoor pool as a functional performance indicator. Anthropometric data and basic clinical information were also collected.

The study was approved by the Lazio Area 5 Territorial Ethics Committee (Approval Code: N.57/SR/23) and conducted in accordance with the Declaration of Helsinki; all participants provided written informed consent before enrollment. By focusing on a feasible dietary modification (greater legume intake) within an otherwise stable Mediterranean-style eating pattern and unchanged training load, the study is designed to generate sport-specific evidence on whether plant-based protein sources such as legumes can enhance cellular hydration, autonomic regulation, and performance-related parameters in competitive athletes.