Calorie calculator (daily energy needs)

The calculator shows you two figures. The first is the total daily requirement, that is the energy you use in an ordinary day, including movement, work and digestion. This is the figure you compare with what you eat.

The second is the resting metabolic rate, the energy the body uses at complete rest, only to breathe, to keep its temperature and to feed its organs. The resting metabolic rate covers the largest part of the daily expenditure, about 75–83% in someone who moves little and around 60% in someone who exercises several times a week. For weight loss, 500–750 kcal a day are usually subtracted from the total daily requirement [1]. The size of the deficit is set together with your doctor or dietitian. A very low-calorie diet, of 800–1000 kcal a day, is followed only under close medical supervision [1].

The resting metabolic rate comes from the Mifflin-St Jeor equation, which uses weight in kilograms, height in centimeters, age in years and sex [2]. Weight is multiplied by 10, height by 6.25 and age by 5. The first two results are added, then the third is subtracted. For men, 5 is added; for women, 161 is subtracted.

For example, a 30-year-old man who weighs 80 kg and is 180 cm tall has a resting metabolic rate of 1780 kcal a day. The total requirement is obtained by multiplying this figure by an activity factor, between 1.2 for a sedentary life and 1.9 for heavy physical work. The calculator above does both steps automatically.

The activity level covers everything you do in a day, not only your training. Someone who works on their feet for eight hours and does no sport moves more than someone who runs three times a week. The runner, however, sits at a desk the rest of the time. Choose the level that matches your ordinary week, not your best week.

The five levels multiply the resting metabolic rate as follows:

• sedentary — desk work and no sport, factor 1.2;
• lightly active — walking or light sport 1–3 days a week, factor 1.375;
• moderately active — moderate sport 3–5 days a week, factor 1.55;
• very active — intense sport 6–7 days a week, factor 1.725;
• extremely active — heavy physical work or two training sessions a day, factor 1.9.

Energy taken in beyond the energy used is stored as fat, and excess fat increases insulin resistance and forces the pancreas to produce more insulin. In a patient with type 2 diabetes, a weight loss of 5–10% improves blood glucose, blood pressure and blood fats [3]. The requirement calculated here tells you where you start from, not what diet to follow.

Calories say little, however, about blood glucose after a meal. What counts there is the amount of carbohydrate, which you count separately — see carbohydrates in type 1 diabetes. Two meals with the same calories can raise blood glucose very differently, depending on how much carbohydrate they contain.