Do You Burn More Calories in the Heat? Here's the Science.

Technically, you do burn more calories in the heat. However, it comes with a major drawback.

During exercise, your body temperature increases to support increased physical demands. To prevent overheating, your body has a tightly controlled heat regulation system, which causes your body to sweat and dissipate heat into the air (1, 2).

If you’re exercising in an already hot environment, your body needs to work even harder to cool your body, which requires more calories. Yet, it’s important to distinguish between a slight increase in calorie expenditure and rapid weight loss (1, 2).

When exercising in hot weather or deliberately overheating your body, such as by wearing heavy clothing, you’ll naturally sweat more to cool your body. Though you may see a drop in body weight after a workout, it’s almost all due to a loss of water weight (2).

Furthermore, your body can easily acclimatize to new environments. While you may initially burn more calories if you’re not used to working in the heat, your body will adapt and gradually require less effort and calories to cool your body (1, 2).

Also, consider your tolerance to exercising in the heat. If you don’t enjoy it or can only sustain it for short periods, you may be better off exercising in a cooler environment you enjoy so you can exercise for longer periods at a greater intensity (3).

All in all, though you may burn a few more calories in the heat, you’re best off choosing exercise you enjoy and can sustain in the long term.

Summary

Though you burn more calories in the heat, its role in weight loss is minimal and decreases as you acclimate to exercising in warmer climates.

Exercising in the heat increases your risk of heat exhaustion, heat stroke, and dehydration.

Signs of heat exhaustion include excessive sweating, clammy skin, weakness, a weak pulse, dizziness, and headache. If you experience any of these symptoms, stop exercising, move to a cool location, and drink plenty of fluids (4, 5).

If left untreated, this can lead to heat stroke, which is characterized by a body temperature of 104°F (40°C) or higher, hot and dry skin, disorientation, and in rare cases, seizures. Heat stroke is a medical emergency and requires immediate medical attention (4, 5).

While you can certainly exercise outside in the heat, there are important considerations to ensure your safety (1, 2):

• Temperature. Always check the current and forecasted temperature before exercising outdoors. The higher the temperature, the greater risk of dehydration and heat stroke.
• Humidity. As humidity increases, there are more water droplets in the air. This makes it more difficult for your body to dissipate heat and sweat.
• Hydration. Drinking water during any exercise is important, but it’s crucial when exercising in hot weather due to increased sweating. Be sure to sip water regularly to replace any lost fluids.
• Experience. If you’re new to exercising in the heat, start slowly and reduce your normal intensity until your body adjusts. This usually takes up to 2 weeks.

As mentioned, knowing the temperature and humidity levels outside will ensure you’re exercising in a safe environment. You’ll need to be more cautious when exercising strenuously outdoors in temperatures above 85°F (about 29°C) (6).

As the temperature and humidity increase, your risk of heat disorders like heat exhaustion and heat stroke increases. Additionally, look out for high relative humidity percentages, which increase your risk despite lower outdoor temperatures.

Using the chart below prior to exercising can help you decide whether it’s safe to exercise outside and if you need to make general adjustments to your regimen, such as wearing lighter clothing, increasing hydration, or lowering your intensity.

Summary

While exercising in the heat is generally safe, always stay hydrated and pay attention to your local heat index warning and signs and symptoms of heat illness.

Ensuring proper fluid intake before, during, and after exercise will help reduce your risk of dehydration. While individual needs vary, here are general guidelines to follow (2, 7, 8):

• Before exercise. Ensure you’re adequately hydrated prior to exercise. For prolonged, intense exercise, drink 2.3–4.5 ounces per pound (5–10 mL per kg) of body weight at least 2–4 hours before exercising.
• During exercise. Replenish any fluids lost during exercise. A good rule of thumb is to drink a few sips of water every 10–20 minutes of exercise. If you’re excessively sweating, you may opt for a sports beverage to replenish lost electrolytes.
• After exercise. For most people, it’s fine to drink and eat as you normally would. If you lost a significant amount of body weight (2% or greater) from sweating, drink 23 ounces per pound (1.5 liters per kg) of body weight lost.

Pre- and post-workout nutrition will largely depend on the type of exercise you perform.

Since exercising in the heat requires more physical effort, ensure you eat a nourishing meal comprising healthy carbs, protein, and fat 1–3 hours before exercising.

Summary

Since exercising in the heat involves increased sweating, it’s crucial to stay hydrated before, during, and after exercising in the heat.

To exercise safely in hot weather, be sure to consider the following (2, 9):

• Wear light, breathable fabrics.
• Stay hydrated with water or a sports beverage.
• Look at your local heat index report. Avoid going out if it’s advised not to.
• Start slowly and lower your intensity as needed.
• Stop if you notice any symptoms of heat exhaustion or heat stroke.
• Wear a hat, sunglasses, and sunscreen (SPF 30 or more).
• Exercise in the early morning or late evening when the temperature is cooler, if possible.

While exercising in the heat may give you an additional challenge, preparing ahead of time can save you from unwanted injury and illness.

If you have a chronic condition, such as diabetes, high blood pressure, or heart disease, always consult a healthcare professional before starting a new exercise regimen.

Summary

By preparing in advance, you can reduce your risk of dehydration and heat illness. However, if weather advisories suggest avoiding outdoor exercise, it’s best to heed this advice.

Exercising in the heat can add challenge to your workout regimen. Though many believe it also helps burn more calories, the effects are minimal.

That said, if you wish to exercise in the heat, there are important safety concerns you’ll need to consider. As the temperature and humidity increase, so do your risks of heat illness and dehydration.

To ensure your safety, be sure to drink plenty of fluids, wear light and breathable fabrics, and always check the heat index report before exercising outdoors. If you’re new to exercising in the heat, start slowly at lower than normal intensities.

While you may burn a few extra calories exercising in the heat, only do so if you enjoy it and can safely tolerate it. Otherwise, exercising in cooler environments is as effective for weight loss.