A new Current Opinion article published in Sports Medicine challenges the growing tendency for endurance athletes to adopt low-FODMAP diets as a default. Instead, the authors make an evidence-based case for a strategic, symptom-severity-led approach.

Exercise-associated gastrointestinal symptoms (Ex-GIS) - flatulence, lower-abdominal bloating and pain, nausea, and urge to defecate - are reported by up to 80% of ultra-endurance runners and can interrupt training and compromise race-day execution. These symptoms are an outcome of exercise-induced gastrointestinal syndrome (EIGS), the pathophysiological response of the gut to exercise. EIGS develops primarily via two pathways:

Substantial GI integrity changes are typically only seen with ≥2 hours of exertional-heat stress or ≥3 hours in temperate conditions - below this threshold, clinically relevant changes are unlikely.

The authors reviewed six experimental studies applying low-FODMAP interventions in endurance athletes. Their position rests on an apparent paradox:

1. Low-FODMAP reduces symptom severity (short-term)

In most trials, low-FODMAP diets were associated with less gut discomfort and reduced total, upper and lower GI symptom severity. Importantly, this appears to reduce symptom severity rather than incidence - athletes may still experience symptoms, but they tend to be milder.

2. High-FODMAP may protect gut integrity

FODMAPs act as prebiotics, driving short-chain fatty acid (SCFA) production that may stimulate epithelial microvascular blood flow and mitigate intestinal injury. In one trial, a high-FODMAP diet increased total faecal SCFA by ~60%. This suggests higher intakes could help protect the gut lining during prolonged strenuous exercise - though at the cost of greater malabsorption and potentially more symptoms.

3. No consistent performance benefit

Only one controlled trial examined performance. Despite greater symptom severity on the high-FODMAP trial, there was no significant difference in distance performance. The authors caution against promoting low-FODMAP diets as performance-enhancing in their own right - any gains are likely secondary to better symptom control.

The authors recommend that FODMAP manipulation be viewed as one component of a broader, individualised GI management plan, not a universal prescription:

Two practical cautions stand out for dietitians/ nutritionists:

• Adequate carbohydrate provision matters. Higher carbohydrate intake (e.g. 45 g·h⁻¹) during exercise can itself ameliorate epithelial injury, sometimes independently of FODMAP content.
• Guard against disordered eating. Low-FODMAP diets should not become a chronic default, particularly in athletes with restrictive eating patterns. Restriction should be time-limited, symptom-driven, and delivered with expert nutrition support and monitoring.