The number of calories you should consume in order to lose weight depends primarily on two factors. These factors are your desired weight-loss rate and the number of calories needed to maintain your current weight. Standard mathematical equations can estimate the number of calories that your daily diet should provide.
Calorie Deficit
To lose weight, you must consume fewer calories than you expend. Your weight-loss rate shouldn't exceed 2 lbs. per week, according to the National Institutes of Health. A pound of body fat is equal to about 3,500 calories, so two pounds is about 7,000 calories. Your calorie deficit should therefore not exceed 1,000 calories per day.
Calorie Requirements
The number of calories you expend each day is the product of your basal metabolic rate and your activity factor. Your basal metabolic rate is your calorie expenditure rate without any activity at all. Your activity factor is a number that represents your level of activity.
Basal Metabolic Rate
Men can estimate their basal metabolic rate with the equation (13.75 x weight) + (5.003 x height) - (6.775 x age) + 66.5. Women use the equation (9.563 x weight) + (1.850 x height) - (4.676 x age) + 655.1. These equations require your weight in kilograms, your height in centimeters and your age in years. Both equations yield your basal metabolic rate in units of calories per day.
Activity Factor
Your activity factor is a measure of your activity level and will allow you to calculate your calorie expenditure rate. This calculation is given by the equation CR = BMR x AF where CR is your calorie expenditure rate, BMR is your basal metabolic rate and AF is your activity factor. Your calorie expenditure rate is the number of calories you need to consume each day to maintain your current weight. You will lose weight if you consume fewer calories than your calorie expenditure rate.
Your activity factor is 1.2 if you're sedentary, 1.375 if you exercise lightly up to three times per week and 1.55 if you're moderately active. Your activity factor is 1.725 if you exercise heavily at least six times per week and 1.9 if your job is physically demanding.
Adjustments
Your calorie requirements will decrease as you lose weight. You must therefore recalculate your calorie requirements regularly and adjust your caloric intake accordingly to continue losing weight. You will need to adjust your caloric intake to match your calorie requirements once you achieve your desired weight.
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