The nutritional value of foods is commonly reported on the packaging of prepackaged and processed foods, and it contains the available energy content for that food. This energy is measured in the form of calories, which stem from the food's fat, protein and carbohydrate content. A calorimeter is most often used to measure the nutritional value of foods as it relates to calories. Molecular chains of chemicals can be isolated and extracted to determine the vitamin and nutrient content of most foods, and this information can be available in most nutritional value of foods charts.
When looking at a chart of the nutritional value of foods, the most common values reported are calories and the amount of grams of the available macronutrients. These macronutrients are protein, fat and carbohydrate, with the last consisting of digestible and non-digestible fiber. The more precise way of measuring the nutritional value of foods in relation to calories is to burn the solid food in a machine called a calorimeter, as one calorie equals the amount of heat it takes to raise 1 gram of water 1 degree Celsius. Most high-tech nutritional machinery can also find the different distributions of the macronutrients, measuring the amount of protein, fat and carbohydrate.
If the nutritional values are already known in relation to their macronutrient content, an individual can simply find the amount of calories available in the food. Each macronutrient contains a certain number of calories per gram, meaning that an individual can find the total sum of these calories. Protein is the most satiating macronutrient and contains only 4 calories per gram. Carbohydrates also contain 4 calories per gram, whereas fat contains 9 calories per gram. Multiplying the number of calories per the number of total grams of each macronutrient and finding the sum will yield the total amount of calories in a particular food.
Determining the value of other nutrients, such as vitamins and minerals, is a more difficult process that usually involves nutritional machinery. Chemicals can be extracted and studied to determine if a certain nutrient's molecular makeup matches a certain vitamin or mineral. The major vitamins like vitamin A and C are often mentioned on the nutrition label on the back of foods, as is calcium and iron. These values are given in relation to a certain serving size or portion measured in grams, helping individuals track their daily nutrient intake.