Exercise and Calories

Caloric balance is the relationship between caloric intake and caloric expenditure — the number of calories taken in from food and drink compared to those expended by basal metabolism and voluntary activity. The energy-balance equation expresses this as Caloric Intake = Caloric Expenditure.

In nutrition and exercise circles, the term "calorie" is frequently used for what is actually a kilocalorie (kcal). A kilocalorie is the amount of heat needed to increase the temperature of 1 kilogram of water by 1° C; one kcal equals 1,000 cal.

Several terms describe the possible relations between intake and expenditure:

• Isocaloric balance — intake and expenditure are equal (e.g. 2,500 kcal/day in and 2,500 kcal/day out); tissue mass neither increases nor decreases.
• Positive caloric balance — intake exceeds expenditure (e.g. 2,800 kcal/day consumed while only 2,500 kcal/day expended, a +300 kcal/day balance). The unexpended 300 kcal are stored as adipose tissue, producing weight gain.
• Negative caloric balance / caloric deficit — expenditure exceeds intake (e.g. 2,500 kcal/day consumed while 3,000 kcal/day expended, a −500 kcal/day deficit). The body primarily uses stored adipose tissue, producing weight loss.

People in physical-activity and weight-reduction programs need to know that balance must be achieved between calories taken in and calories expended in order to stay at the same weight. One pound of adipose tissue equals 3,500 kcal; thus a 3,500-kcal surplus gains 1 lb of fat, and a 3,500-kcal deficit loses 1 lb of fat. A deficit of 500 kcal per day leads to the loss of about 1 lb of adipose tissue in 1 week.

A negative caloric balance can be attained by decreasing caloric intake, increasing energy expenditure through exercise, or combining both — the combination being recommended. The source manual put the ceiling at 1,000–1,200 kcal a day (about 2 lb a week), but clinical guidelines set it lower: a deficit of 500–1,000 kcal/day for about 1–2 lb (0.5–0.9 kg) a week in adults with obesity, and 300–500 kcal/day for a BMI of 27–35 (NHLBI 1998). Lifters who want to keep muscle should aim for about 0.5–1% of body weight a week (see Safe Rate of Caloric Deficit and Weight Loss and Setting Calorie Targets for Fat Loss, Maintenance, and Gain).

• Caloric Intake = Caloric Expenditure (energy-balance equation).
• 1 kcal = heat to raise 1 kg water 1°C = 1,000 cal.
• Isocaloric: 2,500 in / 2,500 out → no change.
• Positive: 2,800 in / 2,500 out = +300 kcal stored as fat.
• Negative: 2,500 in / 3,000 out = −500 kcal deficit → fat loss.
• 1 lb adipose tissue = 3,500 kcal; 500 kcal/day deficit ≈ 1 lb/week.
• Guideline deficit for adults with obesity: 500–1,000 kcal/day ≈ 1–2 lb/week (NHLBI 1998); lifters keeping muscle: ~0.5–1% of body weight/week (corrected 2026-10-13; the manual's 1,000–1,200 kcal ceiling is not supported).