Nutritionists and health professionals constantly caution against excess calorie intake, but unless you sit down with a registered dietitian to create a personalized eating plan, you may be wondering just how many calories you need. The amount of calories your body requires to function is termed basal metabolic rate, or metabolism. Metabolism is determined by your age, sex and body size. The amount of calories your body burns during digestion and physical activity combined with your metabolism equal the amount of calories you need per day for weight maintenance.
Metabolism
Everything you eat is broken down and used to fuel your cells. Muscle mass requires more calories to maintain its function than fat mass does. Because men tend to have more muscle mass than women, men typically have higher calorie needs than women. People with a higher body weight require more energy for their cells to function because there is more mass to sustain. As you age, your calorie needs change. Children and teens who are still growing require different amounts of energy than adults. Older adults possess less muscle mass, which results in fewer calories burned and more fat mass accumulates. Metabolism tends to remain fairly constant, and makes up about 60 to 75 percent of the calories you burn each day. When calculating your personal calorie needs, it is important to take these factors into account.
Digestion
Another factor contributing to your calorie requirement is the thermic effect of food. The thermic effect of food consists of all the digestion and breakdown of food after a meal. This factor also remains fairly constant during your lifetime. The process of digestion represents approximately 10 percent of your daily energy expenditure.
Physical Activity Level
The U.S. Department of Agriculture's Dietary Guidelines for Americans recommends balancing calories in with calories out. The rest of your daily energy expenditure is attributed to your physical activity level. The more physical activity you do, the more calories you burn. Energy balance occurs when you are able to calculate how many calories you burn and replenish them through food and beverage intake.
General Guidelines
For weight maintenance, balance the calories your body needs for metabolism plus an estimate of the thermic effect of food and the amount of calories you burn during exercise and physical activity with the calories you consume. A simple resource for this can be found on the USDA's MyPlate website. For weight loss, calculate your energy needs and either increase your physical activity or decrease the amount of calories you consume. As with any lifestyle change that can affect your health and the way your body functions, consult a physician or registered dietitian before making any drastic changes.
Guidelines for Special Groups
During different life stages, your calorie needs will change. Women who are pregnant or breastfeeding, children and youth and people seeking weight loss all have special dietary requirements. To ensure optimal health, make sure to follow the recommended guidelines for your current stage of life.
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