Every Singapore endurance athlete knows the feeling: a fuel that sits perfectly well on a cool-weather run becomes difficult to stomach on a humid morning when the temperature is already climbing toward 30°C before sunrise. This is not a coincidence, and it is not a failure of willpower. It is physiology.

Heat and humidity can measurably affect gut comfort and fuel tolerance during exercise. Understanding why is the key to fuelling well in Singapore's climate — and to understanding why a fuel format that works for one athlete in the tropics may not work for another, and why testing your own fuel in your own conditions is one of the most important fuelling decisions you make.

What Heat Does to the Gut During Exercise

During exercise, the body faces competing demands for blood flow. Working muscles need oxygen. The skin needs blood flow to dissipate heat through sweating. And the gastrointestinal tract needs perfusion to digest and absorb fuel. Under normal temperate conditions, the body manages these demands with some margin. Under heat stress, the margin narrows considerably.

The research on this is well-established. To dissipate heat from the body's core to the skin surface, the body triggers peripheral vasodilation and sweating — and the resulting large increase in peripheral circulation reduces blood flow to the internal organs. This effect is amplified during exercise, because the working muscles also demand additional blood supply. The consequence is that blood flow is redistributed away from the gastrointestinal system, resulting in reduced total splanchnic perfusion.^[1]

This reduced gut blood flow — splanchnic hypoperfusion — has downstream effects. Research has demonstrated that exercise-induced splanchnic hypoperfusion results in measurable gut dysfunction in healthy individuals, with the effect compounded under heat stress.^[1] A 2025 study in Physiological Reports examined moderate ambient heat stress (28–30°C) versus normal conditions (18–21°C) in trained triathletes performing a one-hour run, and found that core body temperature, heart rate, and perceived exertion were all significantly higher under heat — alongside elevated circulating markers of gastrointestinal integrity disruption.^[2]

The practical translation: in heat, the same gel is being processed under conditions where gut blood flow and absorption comfort may be compromised, leaving the gut less able to absorb and process fuel comfortably than it would be in cool conditions. This is the physiological basis for why fuelling that works in temperate training can become a problem in tropical racing.

Why Singapore's Climate Makes This Especially Relevant

Singapore exposes athletes to heat-stress conditions for a large proportion of the training year. Mean annual relative humidity is approximately 82%, and afternoon temperatures commonly exceed 32°C during inter-monsoon periods, per Meteorological Service Singapore (MSS) climate data.^[3] Humidity compounds the challenge: when ambient humidity is high, sweat evaporates less efficiently, reducing the body's primary cooling mechanism and driving even greater demand for skin blood flow to manage core temperature.

For a Singapore athlete, this means the gut is operating under heat-related perfusion stress for a far greater proportion of training sessions than for an athlete in a temperate climate. The implication is not that fuelling is impossible — Singapore has a thriving endurance community competing successfully year-round — but that gut tolerance is a more central and more constant variable in fuelling strategy here than almost anywhere else.

What Influences How Well a Fuel Is Tolerated

Several factors influence how comfortably the gut tolerates a fuel during exercise, particularly under heat stress. Understanding these helps an athlete diagnose and adjust their own fuelling:

• Carbohydrate concentration and osmolality. A highly concentrated fuel draws water into the gut to dilute it, which can contribute to discomfort. The osmolality of a fuel — its concentration of dissolved particles — influences gastric emptying and the speed at which fluid and carbohydrate move through the system.
• Carbohydrate type and transporter load. As examined in Post 01, single-transporter glucose sources saturate at approximately 60g per hour; exceeding that leaves unabsorbed carbohydrate in the gut, a common trigger for distress. A glucose-fructose combination (such as that naturally present in honey) utilises two intestinal transporters, supporting higher carbohydrate intake of up to approximately 90g per hour in many athletes when well-tolerated.
• Hydration status. Research has shown that exercise-induced dehydration compromises gut integrity independently of heat stress — and the two effects compound. Maintaining hydration is one of the most direct ways to protect gut function during exercise in heat.^[4]
• Fibre, fat, and protein load. Higher fibre and fat content slow gastric emptying, meaning fuel sits in the stomach longer — a particular consideration immediately before and during higher-intensity efforts.
• Individual variation. Gut tolerance is highly individual. Two athletes consuming the identical fuel in the identical conditions can have completely different experiences. There is no universally "best" fuel — only the fuel that works for a given athlete in their conditions.

The Gut Can Be Trained

One of the most encouraging findings in this area of sports science is that the gastrointestinal tract is highly adaptable. The gut is not a fixed-capacity system — the gut can adapt to repeated fuelling practice, improving its capacity to tolerate and absorb fuel over time.

Jeukendrup's 2017 review "Training the Gut for Athletes" in Sports Medicine summarised the substantial body of evidence that gastric emptying, stomach comfort, and carbohydrate absorption capacity can all be improved through deliberate training.^[5] Repeated exposure to carbohydrate intake during training upregulates intestinal glucose transporters and improves tolerance of multiple-transportable carbohydrates, reducing GI distress during competition. Research has indicated that even two weeks of structured gut training can measurably reduce exercise-associated gastrointestinal symptoms.^[5]

The practical methods are straightforward: practise fuelling during training rather than only on race day; train occasionally with fuel in the stomach to build tolerance; and gradually increase carbohydrate intake during longer sessions to condition the gut to higher delivery rates. For Singapore athletes, the additional and important point is that this gut training should happen in Singapore's conditions — conditioning the gut in the heat and humidity it will actually face on race day, not in an air-conditioned gym.

Why "Test Your Fuel" Is the Central Principle

Everything above leads to a practical conclusion that runs through this entire FUELCODE series: the only reliable way to know whether a fuel works for you in Singapore's heat is to test it, repeatedly, in training, under race-representative conditions.

This is not a marketing position — it is the direct implication of the physiology. Because gut tolerance is so individual, and because heat stress amplifies individual differences, no brand can honestly tell you that its fuel will agree with your gut. What it can offer is a fuel worth testing — and the honest advice to test it properly before relying on it in competition.

A practical testing approach:

• Trial any new fuel on easy training sessions first, in the heat, before using it in hard sessions.
• Test it at the intensity and duration of your target event — gut tolerance at easy pace does not always predict tolerance at race pace.
• Pay attention to timing: the same fuel may be tolerated differently 45 minutes before a session versus mid-session.
• Never introduce a new fuel for the first time on race day. This is the single most common and most avoidable fuelling mistake in endurance sport.

Where Nomad Gels Fit

Nomad honey gels are built on an organic Greek honey base, delivering naturally occurring glucose and fructose — the dual-transporter carbohydrate profile that spreads absorption across two intestinal pathways, examined in Post 01. The simpler variants — Pollen and Peanut — offer a short ingredient list that, as discussed in Post 06, gives athletes fewer formulation variables to evaluate when diagnosing their own gut tolerance. The Fir Honey, examined in Post 04, offers a more graduated carbohydrate delivery option supported by honey’s natural medium-GI profile

None of this means a Nomad gel will suit any individual athlete's gut better than another fuel — that claim could only be made with head-to-head testing in each athlete's own conditions, which does not exist. What Nomad gels offer is a whole-food honey carbohydrate fuel formulated which worth testing as part of your own gut-tolerance evaluation in Singapore's conditions.

Test your fuel in the heat — before race day. The Nomad Honey Gel Starter Kit includes all four variants so you can compare taste, timing, energy feel, and gut comfort across real training sessions in Singapore's heat and humidity. No fuel works for everyone; the goal is to find what works for your gut before competition.