The amount of calories you need to consume will largely depend on your nutritional goals, age, weight, activity level and gender. As a general rule of thumb, a woman may need to eat about 1,500 to 2,500 calories per day. If her goal is weight loss, she must consume fewer calories than someone who wants to gain or maintain weight. Knowing your goals and the factors involved will help you determine how many calories you need to eat each day.
Function
Your body uses calories as energy to fuel your day-to-day activities, from working out to sitting at your desk. Everything you do requires energy, which is why a sedentary person may still require a significant number of calories. There are three factors that determine how calories are burned and how many you need to consume. They are your activity level, your basal metabolic rate (BMR) and the thermic effect of food.
Considerations
To understand how much calorie consumption will vary depending on your gender and weight, consider this: On average, a 30-year-old woman who weighs 150 pounds will need to eat 2,070 calories per day to maintain her weight. A woman of the same age who weighs 125 pounds will need to eat 1,831 calories per day. A 30-year-old man who weighs 150 pounds will need to eat 2,256 calories per day.
BMR and Thermic Effect
Your BMR is the amount of calories you burn at rest. It includes calories burned while sleeping, breathing and pumping blood. It accounts for about 60 to 70 percent of your total calories burned. When dieting, you should never consume fewer calories than your BMR. To estimate your BMR, simply multiply your weight by 10. For a more accurate calculation, use the Harris Benedict Equation. For men: BMR = 66 + (13.7 x your weight in kilograms) + (5 x your height in centimeters) - (6.8 x your age in years). For women: BMR = 655 + (9.6 x your weight in kg) + (1.8 x your height in cm) - (4.7 x your age in years).
The thermic effect of food is the amount of calories you burn while eating. It accounts for about 10 percent of total calories burned.
Activity Level
You may be surprised to learn that someone who works out regularly but spends eight hours sitting behind a desk may not necessarily have a high activity level. On the other hand, a nurse in an emergency room who spends 12-hour days on her feet but never works out actually may demand more calories than someone who frequents the gym. Your activity level includes all non-resting activity, such as walking the dog, gardening and working out. The higher your activity level, the more calories you need to consume. Your activity level may account for about 20 to 50 percent of your BMR. The Harris Benedict formula breaks activities into five categories:
Sedentary: BMR x 1.2
Lightly Active: BMR x 1.375
Moderately Active: BMR x 1.55
Very Active: BMR x 1.725
Extra Active: BMR x 1.9
A Healthy Diet
The calories found in food come from proteins, carbohydrates and fats. Your body uses all three to function. Fats help your body absorb nutrients. Carbohydrates provide energy and protein helps build and repair muscles. The U.S. Department of Agriculture (USDA) recommends that 45 to 65 percent of the calories in a healthy diet should come from carbohydrates, 10 to 35 percent from protein and 20 to 35 percent from fat.
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