If you count exits instead of splits, or pulled to the side of a course with cramps that have nothing to do with your legs, you already know that what you eat during a race can be as decisive as how you train for it. GI problems don't just cost you comfort. They cost you output.

The good news: most race-day GI distress is not random. There are well-understood physiological reasons it happens, and equally well-understood nutritional strategies that reduce the risk substantially. Here's what the research shows.

Why your digestion struggles during hard efforts

Three categories of causes account for the overwhelming majority of exercise-induced GI symptoms. Understanding them makes the practical fixes obvious.

The osmotic load problem — and why carb source matters

When you ingest a carbohydrate solution, the gut adjusts fluid to balance the osmotic concentration across the intestinal wall. A solution with a very high osmotic load draws water into the intestinal lumen. The result: bloating, nausea, and discomfort at exactly the wrong time.

Ultra-processed carbohydrates like maltodextrin, dextrose, and corn syrup are common in conventional sports nutrition because they are cheap and shelf-stable. But their extreme speed of absorption is also their problem: they create a rapid, high-osmolality bolus in the small intestine at the moment when gut perfusion is already reduced by exercise.

Whole-food carbohydrate sources — like the basmati rice, honey, and fruit used in Spring Energy gels — have a lower glycemic index, a gentler osmotic profile, and carry naturally occurring compounds that support steady, sustained energy delivery. The result is carbohydrate that fuels hard efforts without overwhelming a gut that is already under circulatory stress.

Lower GI does not mean slower energy delivery. It means the energy arrives more steadily, with a lower osmotic load and without the blood glucose spike-and-crash that leaves you reaching for your next gel ahead of schedule. The whole-food matrix also provides naturally occurring organic acids and bioactive compounds that support absorption — not hinder it.

What the exercise physiology research adds

High-intensity exercise creates measurable increases in intestinal permeability — the so-called "leaky gut" effect. A systematic review in the International Journal of Environmental Research and Public Health found that vigorous endurance exercise triggers upregulation of inflammation markers and increased permeability in athletes, with more consistent effects seen in competitive athletes than in recreational exercisers.³

A separate review in Frontiers in Nutrition found that just 60 minutes of vigorous endurance training at 70 percent of maximum work capacity was sufficient to produce characteristic leaky gut responses, as measured by the lactulose/rhamnose ratio — a standard marker of intestinal permeability.⁴

Practical checklist for a GI-problem-free race

• 1
  Train your gut before race day. Your intestinal transporters adapt to repeated carbohydrate exposure. Practising your race-day fueling strategy in training conditions increases absorption capacity and reduces novelty-driven symptoms on the day.
• 2
  Avoid high-concentration synthetic gel solutions in the 30 minutes before intense efforts. Pre-race loading is best done 2 to 3 hours out. Close-to-start intake of highly processed, concentrated carbohydrate can trigger reactive hypoglycaemia and spike osmotic load right as intensity rises.
• 3
  Take fuel with water, not in isolation. Osmolality is a function of both carbohydrate concentration and fluid volume. A gel taken with 150–200 ml of water is more gut-friendly than the same gel chased with nothing — especially true for high-GI, synthetic products.
• 4
  Time your larger meals carefully. In the 2 to 3 hours before a hard effort, heavy meals high in fibre and fat slow gastric emptying and can increase GI transit time. The small amounts of natural fat found in real-food gels are well tolerated during exercise — it's the large pre-race meal that creates the risk, not the gel on the course.
• 5
  Moderate total carbohydrate dose per feeding. The gut has a ceiling for how much carbohydrate it can absorb per hour — roughly 60 g for single-transporter sources like glucose alone, up to 90 g with multiple transportable carbohydrates. Exceeding this doesn't add more fuel. It adds more osmotic load.
• 6
  Watch your pre-race NSAIDs. Ibuprofen and similar drugs are associated with increased intestinal permeability and GI bleeding risk in endurance athletes. If you rely on them for race-day pain management, it's worth discussing alternatives with a sports medicine professional.
• 7
  Consider carbohydrate source as part of your fueling selection, not just calorie count. Two gels with identical calories can have very different gut outcomes depending on whether the carbohydrate comes from maltodextrin and corn syrup or from whole-food sources like rice, honey, and fruit.

Summary

GI problems during races are not an inevitability. They are largely a function of what happens to the intestinal lining under physiological stress and what you ask it to absorb at that moment. The research on exercise-induced gut permeability, osmotic load, and splanchnic hypoperfusion gives a consistent picture: the gut under exercise stress is more vulnerable, not less.

Fueling strategies built around whole-food carbohydrate sources — lower osmotic load, lower GI, and ingredients the body recognises — reduce that risk meaningfully. Calories in, watts out is still the framework. The source of those calories is what determines whether the system holds.