What is Calorie?

Calorie that we will talk about is the food calorie which is capitalized as Calorie to distinguish it from the chemistry calorie, however, this capitalization is rarely observed in practice.

The Food Calorie

Nutritionists measure the energy content of food in "calories" (sometimes capitalized and abbreviated as Cal or sometimes C, or abbreviated kcal as if small calories were being used), where each food calorie represents 4,186 joules. This is equivalent to 1000 of the calories used in chemistry, and thus the food Calorie would be called a kilocalorie if small calories were being used. However, in chemistry calories have been deprecated as a scientific unit of measure in favor of joules, and therefore in common modern usage the word "calorie" usually refers to a food calorie.

This situation provides two ways of talking about the amount of calories in food which look quite different but that express the exact same amount of energy. One may say that dietary fat has nine kilocalories (kcal) per gram, while proteins and carbohydrates have four kcal per gram, or, one may say that fat has nine Calories per gram while carbohydrates and proteins have four Calories per gram.

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That whose body weight places them into the obese category is obviously seen from the outside. But what about the borderline overweight? Is that ten pounds over the ideal weight raising your risk of health complications? Are you just 'big-boned'?  Do you fall into overweight category?  How do you decide if you really need to lose weight - and how much you need to lose?

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Body Mass Index (BMI)

The body mass index, or BMI, helps clarify an important distinction between being overweight or being obese. If you weigh too much, you're obviously overweight. But if you have a very high proportion of body fat, you're obese. Generally, the BMI will accurately reflect your weight and proportion of body fat as a function of your height and weight when categorizing you as healthy, overweight or obese.

According to the National Heart, Lung and Blood Institute (NHLBI), the BMI "describes body weight relative to height and is correlated with total body fat content in most adults". It is generally an accurate representation of muscle-to-fat ratio, though there are some limitations.

• It may overestimate the BMI of an athletic person, because muscle is denser and weighs more than fat.

• It may underestimate the BMI of an older person, or others who have low muscle mass.

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