The amount of calories you burn per day is determined by a variety of factors -- some genetic and out of your control, and some that you can alter. Your total energy expenditure is the sum of your resting energy expenditure, digestion of food and physical activity. Your resting energy expenditure accounts for the greatest amount of calories burned, while physical activity is the most varied aspect. REE is influenced by age, sex, hormones, body size and body composition. Hot and cold environments also impact your REE and can increase the amount of calories you burn, because of greater demands on your body to maintain a steady temperature.
Factors Influencing Daily Calories Burned
If you were to do nothing but lie in bed all day, your body would still need energy to preserve basic life functions, such as heart rate, temperature, circulation, nerve functioning and breathing. The amount of energy needed to maintain these functions is known as resting energy expenditure, or REE. It's measured in calories, and accounts for 60 to 80 percent of your daily calories burned.
To get a rough estimate of your REE, you can attribute 1 calorie per kilogram of body weight per hour. To determine your weight in kilograms, divide your weight in pounds by 2.2. The REE of a 154-pound male is approximately 1,680 calories a day, while the REE for a 121-pound female is approximately 1,320 calories. You then need to factor in your activity level. If you're sedentary, with a desk job and no exercise, multiply your REE by 1.2. Multiply by 1.375 and 1.55 for exercise one to three days and six to seven days a week, respectively. Very active individuals who exercise twice a day should multiply their REE by 1.725, and if you are training for an endurance event, multiply by 1.9.
You also use energy to digest the food you eat. Five to 10 percent of the calories you ingest are used to digest your food, depending upon the mixture of fat, protein and carbohydrates. The 154-pound male would burn between 84 and 168 calories through digestion.
Hot Versus Cold Temperatures
When it's hot outside, your body works hard to keep you cool so you maintain a steady body temperature. You lose most of the energy manufactured by your muscles during exercise as heat. The more your muscles work, the hotter they become. Your body needs to kick it into overdrive to keep you cool. Your cardiovascular system increases blood flow to your skin so you start to sweat. Exercise inherently raises your body temperature, meaning your body doesn't need to work harder to warm you up. It's already doing that. You burn more fat and calories and can exercise longer when you do so in warm temperatures, according to the American Council on Exercise. Don't go overboard, though. If you experience dizziness, muscle cramps, weakness and headache, stop exercising. These are signs of heat exhaustion, which can be treated by getting to a cooler place and drinking cold fluids.
Calories and Perceived Exertion
Working out in an extremely hot environment may cause you to perceive you're working out harder and burning more calories than you actually are. A study published in 2013 and funded by the American Council on Exercise examined the difference between hot yoga -- which is typically conducted in rooms ranging in temperature from 90 to 105 degrees Fahrenheit -- and regular yoga on core body temperature and heart rate. For the study, subjects participated in 60-minute sessions of both hot yoga and regular yoga, and their core temperatures and heart rates were measured before, during and after the workout. Even though participants were drenched in sweat by the end of the hot yoga session, the results yielded no significant difference in heart rate or body temperature between the two yoga classes. Participants did, however, perceive themselves to be working harder in the hot yoga class compared to the standard yoga class, based on a ratings of perceived exertion scale. Researchers speculated participants may have scaled back on how hard they were pushing themselves due to the warm temperatures, indicating excessive sweating may cause you to believe you're burning more calories than you actually are.
Shivering to Burn Calories
You may feel like your body is working harder to keep you warm when it's cold outside, but you don't start to burn additional calories until you shiver. Shivering is a sign that your body is trying to keep a steady temperature. The calories you burn will vary depending on the outside temperature, how long you've been outside and what type of clothing you're wearing. Be wary of hypothermia, which occurs when your core temperature drops and blood starts to pump away from your arms and legs and to your core to keep you warm. Mild shivering, goose bumps and cold hands are signs of hypothermia. More severe hypothermia can cause uncontrollable shivering, stumbling and difficulty speaking.
Since a study came out in the journal "Cell Metabolism" in 2014, shivering is now being examined as a potential weight loss therapy. Shivering, like exercise, activates the hormone irisin. Irisin prompts brown fat cells to use energy to produce additional heat, which burns extra calories. In the study, participants relaxed in thermoblankets in which the temperature was progressively lowered. The subjects increased the amount of calories they burned under cooler temperatures, and the harder participants shivered, the higher their irisin levels rose. The researchers concluded that shivering rouses your brown fat tissue to keep your core temperature in a healthy range, even if your skin temperature falls. The study was small, however, and more research is needed before shivering should be recommended to remedy overweight and obesity.
- Nutrition for Health, Fitness and Sport: Human Energy
- American Council on Exercise: Daily Caloric Needs Estimator
- American Council on Exercise: Do I Burn More Calories When It's Hot or Cold Outside?
- University of Maryland Medical Center: Heat Exhaustion
- U.S. Center for Sports Medicine: How Cold is too Cold to Exercise in the Winter?
- National Institutes of Health Shivering Triggers Brown Fat to Produce Heat and Burn Calories
- Cell Metabolism: Irisin and FGF21 Are Cold-Induced Endocrine Activators of Brown Fat Function in Humans
- Kansas State University: Physical Activity and Controlling Weight
- American Council on Exercise: Hot Yoga - Go Ahead and Turn Up the Heat