Does the body absorb carbohydrates the same in cold as in hot weather?

Those who have participated in races at different times of the year have probably found that the same nutritional strategy doesn't always work the same way.

An energy gel that was perfectly tolerated during a winter training session can be much more difficult to consume in a competition held in intense heat.

But is it just a subjective feeling? The answer is no.

Scientific evidence shows that ambient temperature directly influences various physiological processes related to digestion, nutrient absorption, and gastrointestinal tolerance during exercise.

Understanding these differences can help athletes better plan their intake of carbohydrates, fluids, and electrolytes, reducing the risk of digestive discomfort and improving performance.

 

What happens in the body during exercise in the heat?

During a prolonged race or training session, the body generates a large amount of heat. To prevent an excessive increase in body temperature, it activates different cooling mechanisms, the main one being sweating.

At the same time, there is a redistribution of blood flow. More blood is directed to the skin to facilitate heat dissipation to the environment.

This adaptation is crucial for regulating body temperature, but it has an important consequence: less blood flow is available for some internal organs, including the digestive system.

The higher the ambient temperature, the greater the competition for blood flow between muscles, skin, and the intestines.

 

The gut takes a back seat

When it's hot, the body prioritizes the most important functions to maintain performance and survival.

Muscles need oxygen to continue producing energy and the skin requires a greater blood supply to promote heat loss.

As a result, the digestive system receives less blood flow.

This phenomenon, known as splanchnic hypoperfusion, has been widely described in scientific literature. When it occurs, various physiological processes can be affected, including:

• Slower gastric emptying.
• Reduced water and nutrient absorption.
• Increased intestinal permeability.
• Higher risk of gastrointestinal discomfort.

For this reason, many athletes describe the sensation of having a "stopped stomach" during competitions held in very hot conditions.

 

Why is gastrointestinal discomfort more frequent in hot weather?

Nausea, reflux, abdominal cramps, feelings of heaviness, and even episodes of diarrhea are relatively common in endurance events. Although there are multiple factors that can cause these symptoms, high temperatures are one of the main ones.

When the intestine receives less blood flow, its function is temporarily compromised. In addition, dehydration, very common in hot environments, can further aggravate this situation.

Various studies show that heat increases the physiological stress of exercise and promotes alterations in the intestinal barrier. In some cases, this facilitates the passage of inflammatory substances into the bloodstream, increasing digestive discomfort and reducing tolerance to intake.

That's why it's not uncommon for an athlete to be able to consume large amounts of carbohydrates during training in mild temperatures, but then struggle to do so in competitions held in intense heat.

 

Does cold weather change this situation?

Generally speaking, yes.

In lower temperatures, the body needs to dedicate fewer resources to body cooling. As a result, blood flow redistribution is usually less pronounced, and the digestive system maintains more efficient functioning during exercise than in extreme heat conditions.

In addition, athletes usually present:

• Lower sweating rate.
• Lower risk of dehydration.
• Lower cardiovascular stress.
• Better gastrointestinal tolerance.

This doesn't mean that cold is automatically better for performance, but it does help explain why many people find it easier to fuel during exercise when temperatures are cool or moderate.

 

So, does heat reduce carbohydrate absorption?

That's a very interesting question.

Current scientific evidence suggests that the main problem is not that the intestine loses the ability to absorb carbohydrates, but that the set of physiological changes makes it difficult for them to reach the place where they should be absorbed adequately.

In other words, heat can make it difficult to:

• Empty the stomach.
• Transport fluids to the intestine.
• Maintain gastrointestinal comfort.
• Sustain a high carbohydrate intake during exercise.

In practice, this means that the nutritional strategy must be planned with greater care when temperatures are high.

 

What can athletes do?

The good news is that the gut can also be trained. Just as we train muscles or the cardiovascular system, it is possible to adapt the digestive system to better tolerate carbohydrate intake during exercise.

Some recommended strategies are:

Train carbohydrate intake

Don't save energy gels for race day. The gut responds better when it gets used, during training, to the amounts of carbohydrates that will be consumed during the race.

Adjust hydration

Dehydration increases gastrointestinal stress. Therefore, maintaining proper fluid and electrolyte replacement is essential, especially in hot weather.

Avoid trying new products

The greater the demands imposed by heat, the less advisable it will be to experiment with new products or nutritional strategies during competition.

Fractionate intake

Consuming small amounts of carbohydrates regularly is usually more comfortable than ingesting large doses in a few moments.

Prioritize products with high gastrointestinal tolerance

Formulations designed to facilitate gastrointestinal transit can contribute to a more comfortable experience during prolonged exercise.

 

Conclusion

Your gut doesn't function exactly the same during a race held at 12 °C as it does in one held at 32 °C.

Heat increases the physiological stress of exercise, promotes the redistribution of blood flow to the muscles and skin, and can increase the risk of gastrointestinal discomfort. Although this does not necessarily imply a reduced ability to absorb carbohydrates, it can make their intake and tolerance difficult during competition.

Therefore, understanding how the environment influences the body's response is as important as choosing the right amount of carbohydrates.

A good nutritional strategy does not only depend on what you consume, but also on the conditions in which your body has to perform.

And the better trained your gut is to cope with those conditions, the greater the chances of maintaining energy, digestive comfort, and performance until you cross the finish line.

You may also be interested in: Mental fatigue and the influence of nutrition.

References:

Jeukendrup AE. Training the Gut for Athletes. Sports Medicine. 2017;47(Suppl 1):101-110.

Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome—implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics. 2017;46(3):246-265.

van Wijck K, Lenaerts K, Grootjans J, et al. Physiological exercise induces splanchnic hypoperfusion and intestinal injury in healthy men. PLoS One. 2011;6(7):e22366.

Lambert GP. Stress-induced gastrointestinal barrier dysfunction and its inflammatory effects. Journal of Animal Science. 2009;87(14 Suppl):E101-E108.

Périard JD, Eijsvogels TMH, Daanen HAM. Exercise Under Heat Stress: Thermoregulation, Hydration, Performance Implications and Mitigation Strategies. Physiological Reviews. 2021;101(4):1873-1979.

de Oliveira EP, Burini RC. Food-dependent, exercise-induced gastrointestinal distress. Journal of the International Society of Sports Nutrition. 2014;11:12.