There are many factors that influence how many calories you burn, including your genes, your body composition and, yes, even the temperature outside.
But do you burn more calories in the heat or cold? And how much of an effect does the temperature really have on your metabolism? Read on to find out.
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You Burn More Calories in Hot Temperatures
Turns out, hot weather causes a greater calorie burn than cold weather.
"In general, you burn more calories when you are hot (or in hot, humid weather) because your cardiovascular system has to do more work to pump blood. Your heart works harder to pump blood to your muscles, which are using more energy," says John P. Higgins, MD, FACC, professor of cardiovascular medicine and sports cardiology at McGovern Medical School, UTHealth in Houston.
Working up a sweat is your body's way of cooling you down, according to the Cleveland Clinic. But does sweating burn calories? Well, it may be a sign that you are burning more calories because, as Dr. Higgins explains, "your cardiovascular system is working harder to send blood to your skin to cool you down."
You may also notice a slight weight loss directly after working out in heat. This is just a loss of water weight; it will return once you rehydrate, per the University of Miami.
And as your body becomes acclimated to exercising in the heat (usually after about 14 days), you may no longer get that extra calorie burn over time, per a November 2016 study in Sports Medicine.
Keep this in mind next time you're running in the heat and need to determine your desired calorie burn and/or calorie deficit for the day.
Is It Safe to Exercise in Hot Weather?
While you may burn more calories in hot weather, you also put a lot more stress on your body. This can be dangerous if you're not careful.
The combination of exercise and heat can increase your body temperature into a range where you push past your body's ability to cool itself by sweating. This puts you at risk for a heat-related illness like heat exhaustion or heatstroke, which may require you to receive immediate medical attention, according to the Mayo Clinic.
Signs of heat exhaustion include the following, per the Centers for Disease Control and Prevention (CDC):
- Heavy sweating
- Elevated body temperature
- Decreased urine output
Visit the nearest emergency room if you experience confusion, slurred speech, loss of consciousness, hot/dry skin or profuse sweating, seizures and very high temperature. These are all signs of heatstroke, which is a serious illness, per the CDC.
Does Being Cold Burn Calories?
Cold weather, on the other hand, doesn't increase calories burned unless you get really cold and start to shiver, according to the National Institutes of Health.
Shivering is a sign your body is working really hard to keep your body temperature normal, and all that extra work produces a calorie burn (although the exact amount of calories you burn shivering will depend on your individual metabolism and other factors).
As for working out in the cold?
"Sure, if you are shivering you also burn more calories, but most people exercising in the cold have proper cold-weather gear on and are not shivering, and they warm up fairly quickly," Dr. Higgins says.
Bottom line? Burning calories through shivering is possible, but it's uncomfortable and potentially dangerous — being exposed to very cold temperatures for long periods puts you at risk for hypothermia, per the CDC, which can be deadly.
Stick with burning calories through regular exercise (and remember, you're always burning calories, even when you're sitting still or sleeping).
Warning signs of hypothermia include shivering, exhaustion, confusion, memory loss and slurred speech, per the CDC. Get medical help immediately if you have these signs and/or a temperature below 95 degrees Fahrenheit.
What Is the Ideal Temperature for Exercise?
"You burn more calories when you exercise in the heat. However, the best range of temperature to burn fat and calories, and to exercise longer, is around 68 degrees, so I recommend that temperature," Dr. Higgins says.
"The more intensely you exercise, the more calories you burn. Exercising in higher temperatures, like 100 degrees, burns more calories from glycogen and less from fat," Dr. Higgins adds. But this is often not sustainable or healthy.
Exercising in the heat will likely cause you to burn more calories, as your heart works harder to pump blood to your muscles.
Ultimately, how many calories you burn under any condition, whether hot or cold, depends on your individual metabolism, size of your body, your body composition and your age, per the Mayo Clinic.
1. Why Do I Weigh More in Hot Weather?
Your weight may fluctuate up a few pounds in hot weather due to water retention. When it's hot out, your body can swell, especially in your ankles, knees and feet, as a result of fluid being stored. The swelling can also be due to a sensitivity to the heat, per Harvard Health Publishing.
While this may cause the number on the scale to go up a bit, it is very minimal and temporary. Once you return to cooler temperatures for a length of time, you'll notice swelling in your body going down, per Harvard Health Publishing.
2. Does Hot Weather Increase Metabolism?
A June 2015 study in the Journal of Experimental Biology found that as temperature increases, metabolism increases, but then rapidly declines as temperatures gets higher. This is called the thermal performance curve.
This means while hot weather can increase your metabolism at first, it eventually decreases the hotter it gets.
So try to focus more on improving your metabolism in other ways, like getting regular exercise and eating consistent balanced meals.
3. Is It Safe to Work Out in Hot or Cold Weather?
While it's safe to work out in the elements, you may need to take extra precaution in temperatures below 32 degrees Fahrenheit and above 85 degrees Fahrenheit.
There are some steps you can take to make it even more safe and effective for your workout goals and overall health.
In the heat, this could mean:
- Checking the temperature and humidity levels through a weather forecast before going outside
- Bringing along extra water (and sipping on it throughout the entire workout)
- Wearing breathable fabrics
- Starting the workout slowly
- Avoiding exercising in the middle of the day, when the sun's the strongest (between 10 a.m. and 2 p.m.)
- Staying in the shade as much as possible
- Wearing sunscreen if in the sun
- Taking plenty of breaks
Working out in the cold could mean the following, per the National Institutes of Health.
- Wearing extra layers for warmth (including waterproof jackets, vests, etc.)
- Finding proper footwear to support your feet in snow, ice and rain
- Getting warm right after exercise
- John P. Higgins, MD, MBA (Hons), MPhil, FACC, FACP, FAHA, FACSM, FASNC, FSGC, professor of cardiovascular medicine, sports cardiology, McGovern Medical School, Houston, Texas
- Cleveland Clinic: “Breaking a Sweat: Why You Sweat and What It Says About Your Health”
- American Council on Exercise: “Resting Metabolic Rate: Best Ways to Measure It—and Raise It, Too”
- Mayo Clinic: “Metabolism and Weight Loss: How You Burn Calories”
- National Institutes of Health: "Five Tips for Exercising Safely During Cold Weather"
- Harvard Health Publishing: "Ask the doctor: Could a sudden gain in weight be caused by hot weather?"
- Journal of Experimental Biology: " The effects of temperature on aerobic metabolism: towards a mechanistic understanding of the responses of ectotherms to a changing environment"
- Centers for Disease Control and Prevention: "Heat Stress-Heat Related Illness"
- University of Miami: "Sweating: Is Wetter Better for Weight Loss?"
- Sports Medicine: "The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis"
- National Institutes of Health: "Shivering Triggers Brown Fat to Produce Heat and Burn Calories"
- Centers for Disease Control and Prevention: "Hypothermia"