This Calorie Calculator is based on the Mifflin-St Jeor Equation which calculates basal metabolic rate (BMR), and its results are based on an estimated average. The basal metabolic rate is the amount of energy expended per day at rest. There exist other equations including the Harris-Benedict Equation which was used until 1990 before the introduction of the Mifflin-St Jeor Equation and the Katch-McArdle Formula which calculates resting daily energy expenditure (RDEE) by taking lean body mass into account. The Mifflin-St Jeor Equation is considered the most accurate equation for calculating BMR, with the exception that the Katch-McArdle Formula can be more accurate for people who are leaner that know their body fat percentage. The Mifflin-St Jeor Equation is as follows:
BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(y) + 5
BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age(y) - 161
The value obtained from this equation is the estimated number of calories a person can consume in a day to maintain their body-weight assuming they remain at rest. This value is multiplied by an activity factor (generally 1.2-1.95) dependent on a person's typical levels of exercise in order to obtain a more realistic value for maintaining body-weight (since people are less likely to be at rest throughout the course of an entire day). 1 pound of body weight, or approximately 0.45 kg, equates to about 3,500 calories. As such, in order to lose 1 pound per week, it is recommended that 500 calories be shaved off the estimate of calories necessary for weight maintenance per day. For example, if a person has an estimated allotment of 2,500 calories per day to maintain body-weight, consuming 2,000 calories per day for one week would theoretically result in 3,500 calories (or 1 pound) lost during the period.
It is important to remember that proper diet and exercise is largely accepted as the best way to lose weight. It is inadvisable to lower calorie intake by more than 1,000 calories per day, as losing more than 2 pounds per week can be unhealthy, and can result in the opposite effect in the near future by reducing metabolism. Losing more than 2 pounds a week will likely involve muscle loss, which in turn lowers BMR since more muscle mass results in higher BMR. Excessive weight loss can also be due to dehydration, which is unhealthy. Furthermore, particularly when exercising in conjunction with dieting, maintaining a good diet is important, since the body needs to be able to support its metabolic processes and replenish itself. Depriving the body of nutrients it requires as part of heavily unhealthy diets can have serious detrimental effects, and weight lost in this manner has been shown in some studies to be unsustainable, since the weight is often regained in the form of fat (putting the participant in a worse state than when beginning the diet). As such, in addition to monitoring calorie intake, it is important to maintain levels of fiber intake as well other nutritional necessities to balance the needs of the body.