Summer is an ideal time to build up cycling mileage, run in the mountains, or prepare for the major events of the new season. But when the thermometer exceeds 30 °C, physiological demands change considerably. The body must not only provide energy to support the effort, but also mobilize significant resources to maintain its internal temperature.

This increase in heat stress leads to heavier sweating, greater water and electrolyte loss, reduced appetite, and, for some athletes, a higher risk of digestive problems or decreased performance.

The good news is that by adapting your diet and hydration before, during, and after exercise, it is possible to limit these effects and continue to perform, even when conditions are particularly hot.

Why does heat change your nutritional needs?

During exercise in hot weather, more blood flow is directed toward the skin to release heat through sweating. This adaptation is essential for maintaining body temperature, but it temporarily reduces blood flow to the digestive system.

Consequences:

• slower digestion;
• an increased risk of nausea or digestive problems;
• an increase in fluid losses;
• a significant loss of sodium and other electrolytes;
• an earlier feeling of fatigue.

For some athletes, sweat losses can exceed 1 to 2 liters per hour, or even more depending on the environmental conditions and training level.

Before exercise: prepare your body

When temperatures are high, preparation begins several hours before the start.

Focus on good hydration

The goal is not to drink large quantities just before setting off, but to arrive at the start already well hydrated.

A few tips:

• drink regularly throughout the day or the day before the race;
• prioritize water and low-sugar drinks;
• check the color of your urine: pale yellow is generally a sign of good hydration.

Choose an easy-to-digest meal

Before a long outing or competition, prioritize:

• easily digestible carbohydrates (rice, pasta, potatoes, bread);
• a source of lean protein;
• little fat;
• little fiber if the exercise is intense.

Conversely, meals that are very rich, spicy, or particularly high in fat can increase the risk of digestive discomfort.

During exercise: adjust intake

Heat changes the way the body uses nutrients.

Drink regularly

Waiting until you feel thirsty is often too late.

One strategy is to drink small amounts every 10 to 20 minutes, adjusting the volume to your sweat rate. You can perform sweat tests, or a simpler solution is to weigh yourself before and after training to determine how much water you have lost.

General recommendations place needs between 400 to 800 mL per hour, but some athletes will need more.

Don't forget sodium

Sweating mainly eliminates:

• sodium;
• chloride;
• smaller amounts of potassium, magnesium, and calcium.

When exercise lasts longer than an hour, especially in hot conditions, a drink containing sodium generally helps compensate for losses better than water alone.

Adjust carbohydrate intake

Heat can sometimes slow gastric emptying and reduce digestive tolerance.

Under these conditions, it may be worth prioritizing:

• sports drinks;
• gels accompanied by water;
• energy purées or fruit compotes;
• more frequent but smaller servings.

Current recommendations generally suggest:

• 30 to 60 g of carbohydrates per hour for efforts lasting 1 to 2 hours 30 minutes;
• 60 to 90 g/h for prolonged efforts, or even up to 120 g/h in some trained athletes using glucose-fructose mixtures who have trained their digestive system.

After exercise: recover effectively

Recovery is particularly important after exercise performed in intense heat.

Replenish fluid stores

The best strategy is to gradually replace water losses. A drink containing some sodium also facilitates fluid retention.

Replenish glycogen stores

In the hours following exertion, prioritize:

• quality carbohydrates;
• fruit;
• starchy foods;
• recovery drinks if necessary.

Promote muscle repair

Combine 20 to 30 g of high-quality protein within the two hours following exercise promotes muscle recovery and protein synthesis.

Adapt your strategy according to the temperature

The most common mistakes

When temperatures exceed 30 °C, certain mistakes recur regularly:

• wait until you are thirsty to drink;
• drink only water during several hours of exertion;
• eat meals that are too rich before the start;
• test a new gel on competition day;
• neglect recovery after the session.

In summary

When the temperature exceeds 30 °C, the priority is no longer just to provide enough energy: you must also help the body maintain its fluid and thermal balance. Regular hydration, an appropriate sodium intake, well-tolerated carbohydrates, and careful recovery help limit the effects of heat on performance.

As with training, the nutrition strategy must be personalized. Testing your nutrition during training, knowing your sweat rate, and gradually adjusting your intake are the best ways to approach summer outings and competitions with peace of mind.