# A gluten-free diet does not alter performance outcomes in nonceliac athletes undergoing sprint interval training: a pilot trial

## TL;DR

A gluten-free diet combined with sprint training slightly improves weight and performance in non-celiac athletes, but does not significantly change metabolism.

## Contribution

This pilot study is among the first to compare gluten-free and mixed diets in non-celiac athletes undergoing sprint interval training.

## Key findings

- A gluten-free diet led to greater weight and BMI reductions compared to a mixed diet.
- Both groups improved time trial performance and time to exhaustion, with no significant differences between them.
- Gluten-free diets showed mixed effects on metabolic parameters and no changes in gastrointestinal quality of life.

## Abstract

The popularity of gluten-free diets (GFD) among athletes has increased due to perceived benefits for performance, well-being, and body composition, despite limited evidence in non-celiac individuals.

This parallel-group pilot study evaluated the effects of a 6-week GFD vs. a mixed diet (MD), both combined with sprint interval training (SIT), on metabolic and performance-related parameters in 15 male endurance athletes (GFD: n = 6; MD: n = 9). Outcomes included body composition, time trial performance (distance during a 60 min run on a 400-metre track), metabolic (respiratory exchange ratio (PER), substrate oxidation rates, maximal fat oxidation [MFO], and FatMax—intensity at which MFO occurs), and performance-related (ventilatory threshold [VT], respiratory compensation point [RCP], peak oxygen uptake [V̇O2peak], and time to exhaustion [TTE]) markers during a ramp incremental running test. Gastrointestinal quality of life (GIQLI) was also assessed.

The GFD group achieved significant reductions in weight and BMI compared to the MD group (Δweight: GFD: −2.70 [−3.20 to −1.73] kg vs. MD: −0.30 [−1.75 to 1.35] kg, p = 0.018, r = 0.569; ΔBMI: GFD: −0.75 [−1.00 to −0.50] kg·m−² vs. MD: −0.10 [−0.55 to 0.35] kg·m−², p = 0.026, r = 0.549). Both groups demonstrated improved time trial distance (Δ: GFD: 0.76 [0.56 to 1.57] km vs. MD: 0.60 [0.50 to 0.90] km, p = 0.313, r = 0.328) and TTE (Δ: GFD: 1.24 [0.61 to 1.80] min vs. MD: 0.70 [0.19 to 0.92] min, p = 0.088, r = 0.442), with V̇O2peak increases appearing more pronounced in the GFD group (ΔV̇O₂peak: GFD: 9.10 [1.80 to 12.38] ml·kg−1·min−1 vs. MD: 3.20 [−1.95 to 10.40] ml·kg−1·min−1, p = 0.388, r = 0.246). Group differences in metabolic changes were mixed (ΔMFO: GFD: 0.075 [−0.070 to 0.190] g·min−1 vs. MD: 0.200 [−0.145 to 0.310] g·min−1, p = 0.607, r = 0.152; ΔFatMax: GFD: −12.90 [−23.56 to 1.79] %V̇O₂peak vs. MD: 1.00 [−10.23 to 12.11] %V̇O₂peak, p = 0.181, r = 0.365), and GIQLI scores showed no significant changes.

Although a GFD showed modest benefits for weight management and aerobic performance, its metabolic effects were variable, and challenges with nutritional deficiencies highlight the need for caution in non-celiac athletes.