Exercise without stomach trouble: a pre-workout checklist

Exercise is one of the better habits for your gut, right up until the moment it isn't. Heartburn halfway through a workout class, cramping on a run or a sudden search for a bathroom on the trail can make you wonder whether it's worth it.

It usually is. Researchers group exercise-related gut symptoms into three broad causes: physiological, mechanical and nutritional (de Oliveira et al., 2014). Several of those are things you can adjust. Use this checklist before your next session.

First, how common is this?

Gut symptoms during exercise are well documented, especially in endurance sports. A review estimated that 30% to 50% of athletes experience them. Most are mild and not a health risk, although rare serious problems, such as bleeding, can occur. One of the main drivers is reduced blood flow to the gut during intense exercise, especially when someone is low on fluids (de Oliveira et al., 2014).

Checklist: timing

• Leave a gap after eating. In a study of 30 conditioned athletes who got heartburn with exercise, 10 weightlifters, 10 runners and 10 cyclists exercised both fasting and after a meal. In all three groups, there was more reflux after eating (Collings et al., 2003). Many people do better with a light snack an hour or so before exercise, or a full meal a few hours before. Experiment to find your own window.
• Be extra careful with lifting after meals. In that same study, weightlifters had the most heartburn and reflux, with acid in the esophagus about 36% of the time when they exercised after eating. Runners had moderate reflux, and cyclists had the least.
• Warm up gradually. Starting with 5 to 10 minutes of easy movement gives your body time to adjust before you pick up the pace.
• Work around your bathroom rhythm. If mornings are your usual bathroom time, a workout after that window may feel better than one before it.

Checklist: intensity and type

• Know where the threshold is. A systematic review found that significant gut disturbances appear with about 2 hours or more of exercise at a steady moderate effort, around 60% of maximum aerobic capacity. Heat and running made them worse (Costa et al., 2017).
• Increase gradually. In that review, gut disturbances rose as both intensity and duration went up. Add time or effort in small steps.
• Swap impact on sensitive days. If running upsets your gut, cycling or brisk walking may be gentler options. Cyclists had the least reflux in the study above.
• Take it easier in the heat, especially if your gut is already unsettled.

Checklist: fluids

• Start well hydrated. Drink normally through the day instead of gulping a large amount right before you start.
• Sip during longer sessions. Being low on fluids during intense exercise is linked with reduced blood flow to the gut (de Oliveira et al., 2014).
• Skip fizzy drinks right before a workout if carbonation tends to make you burp or feel full.

Checklist: food

• Keep pre-workout food familiar. The day of a long hike or a new class isn't the time to try a new bar, gel or high-fiber snack.
• Watch fast-fermenting carbs before hard sessions. In a small crossover trial, 11 recreational runners with exercise-related gut symptoms ate a low-FODMAP or a high-FODMAP diet for six days each. On the low-FODMAP diet, their daily gut symptoms were lower, including gas, urgency and loose stools, though symptoms during exercise didn't differ significantly (Lis et al., 2018). Inulin is one common FODMAP in "healthy" snacks.
• Know your personal triggers. If sugar alcohols, rich foods or large portions bother you on normal days, keep them out of your pre-workout snacks.

Checklist: bathroom logistics

• Give yourself a few minutes to use the bathroom before you start.
• While you're figuring out your triggers, choose walking or running routes with restroom access.
• If urgency is a pattern, note when it happens: the time of day, what you ate and how hard you pushed.
• After a session, cool down with a few minutes of walking, drink to replace what you lost, and eat a normal meal once your stomach feels settled.
• Give changes a few weeks. One bad workout doesn't make a pattern, but three or four similar notes usually do.

When to stop and get checked

Stop exercising and get urgent medical help for chest pain, pressure or tightness, especially with shortness of breath, sweating, nausea or dizziness. Heartburn and heart symptoms can be hard to tell apart, and it's not worth guessing.

See your doctor if you notice blood in your stool after exercise, black stools, severe or worsening abdominal pain, vomiting, or gut symptoms that now show up even during easy activity. Symptoms that are new in midlife deserve a check rather than a workaround.

Sources

1. de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med. 2014;44(Suppl 1):S79-85. PMID 24791919
2. Collings KL, Pierce Pratt F, Rodriguez-Stanley S, Bemben M, Miner PB. Esophageal reflux in conditioned runners, cyclists, and weightlifters. Med Sci Sports Exerc. 2003;35(5):730-5. PMID 12750580
3. Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Aliment Pharmacol Ther. 2017;46(3):246-265. PMID 28589631
4. Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK. Low FODMAP: a preliminary strategy to reduce gastrointestinal distress in athletes. Med Sci Sports Exerc. 2018;50(1):116-123. PMID 28891824

This article is for general information and isn't medical advice. Check with your healthcare provider before starting vigorous exercise, and seek urgent care for chest pain or other worrying symptoms during activity.