Maintaining your body temperature is a function of your metabolism -- specifically your basal metabolic rate, or BMR. Your BMR is the amount of calories you burn at rest and can account for between 50 and 80 percent of all the energy you use. Individual caloric requirements will vary based on age, activity level, gender and body composition -- muscle requires more energy than fat.
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A calorie is a unit of energy, it measures heat -- specifically it's a measurement of the amount of energy required to raise the temperature of 1 gram of water by 1 degree C. Nutritionists use the word calorie to describe the potential food has to give your body energy. The more calories in food, the greater the amount of energy you will have to use. Excess energy that you can't use immediately is stored for later use -- as a form of fat known as triglycerides.
There are three parts to your metabolism. Your BMR, which maintains body temperature and keeps you alive is the energy used to circulate blood, keep your heart beating and the many other involuntary chemical processes happening constantly in your body. Then there is the energy used for movement and the energy used for digestion -- called thermogenisis. Up to 80 percent of the calories you eat are used by your BMR, about 20 percent go to physical activity and only 5 to 10 percent are used for digestion, according to the Better Health Channel. Digesting protein requires more energy than digesting fats or carbohydrates.
Calories and Metabolism
The number of calories you need to maintain your basal metabolic rate depends on your age and gender. The National Heart, Lung and Blood Institute notes that a woman needs a minimum of 1,200 calories and a man needs at least 1,500 calories each day to maintain basic metabolic function. Then you need to add calories for your activity level -- the more exercise you do, the more calories you'll need to add to maintain your weight. If you want to lose weight, you may not need to add more calories -- but you must eat the minimum calories needed to maintain your BMR. If you don't consume enough energy, your body thinks you are starving and slows your metabolism to conserve energy -- it's a biological survival mechanism.
Calorie Restriction and Body Temperature
A study in the April 2011 issue of "Aging" reports that some people purposely practice calorie restriction because they believe that it will increase their life-span while keeping them disease free. The study examined the effects of calorie restriction on these subjects and found that even though they took in adequate amounts of nutrients, they still had lower core body temperatures compared to those who ate a typical western diet and exercised to reduce calories. Researchers confirm that the body lowers its temperature in response to lower energy intake to save energy.