According to the Centers for Disease Control and Prevention, calories are the units of energy provided by food. Although calories come from carbohydrates, fats, proteins and alcohol, the source of calories is not as important as the quantity when determining calorie balance. The required number of daily calories for women depends on how many calories they expend each day, and whether they want to lose, gain or maintain current weight. Controlling weight is one of the most important health choices a woman can make.
Components
According to the Mayo Clinic, there are three components to the total daily calorie needs for women. The first is basal metabolic rate, or BMR. This component makes up about 60 to 75 percent of total daily needs and the Harris Benedict equation can estimate a woman's BMR, or the number of calories she needs for basic functions. Thermogenesis, the second component, makes up about 10 percent of the required daily calories and is the energy your body uses to digest the food you eat. Physical activity is the third and most variable component of total needs.
BMR
Your basal metabolic rate, or BMR, is the number of calories you use in a day for basic functions such as breathing, keeping your heart beating and maintaining the cells in your body. According to the Mayo Clinic, BMR depends on factors such as height, weight and age. A greater height and weight raises your BMR while your BMR decreases as you grow older. A 25-year-old woman who is 5 feet, 8 inches tall and weighs 150 pounds has a BMR of about 1,475 calories per day. A 60-year-old woman who is 5 feet, 3 inches tall has a BMR of about 1,088 calories. Your BMR is adaptive and decreases slightly if you do not eat enough, such as during an extreme diet.
Body Composition
A woman's body composition affects her required daily calories because muscle mass has a higher metabolic rate than fat mass. Women who have a higher percentage of muscle mass have a higher BMR than women with more fat. Since men, in general, have a higher percentage of lean muscle than women, a woman would be likely to have a lower BMR than a man with the same height and weight. According to BMRCalculator.org, a 30-year-old woman who is 5 feet, 8 inches tall and weighs 160 pounds has a BMR of about 1,450 calories, while a man of the same age, height and weight has a BMR of about 1,617 calories.
Physical Activity
Physical activity includes purposeful exercise and any other movement throughout the day. It is the most variable component of calorie needs for women. The Centers for Disease Control and Prevention recommends that you exercise each week for at least 2.5 hours at a moderate or vigorous intensity to maintain weight, and you can exercise more to lose weight. Use a calculator or chart such as the interactive database at MayoClinic.com to estimate the amount of calories you burn through exercise. A woman who needs about 1,700 calories if she is sedentary might require around 2,800 calories per day if she is a competitive athlete.
Weight Loss
The number of required daily calories for a woman becomes lower if she wants to lose weight because losing weight requires taking in fewer calories than you use. A pound of body fat equals about 3,500 calories, and most experts agree that healthy weight loss is at the rate of 1 to 2 pounds a week. This means creating a calorie deficit of about 500 to 1,000 per day. A woman can either eat fewer calories or increase calorie needs by exercising more. Exercise can burn hundreds of calories per hour.
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