Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
Protein milkshakes, made from protein powder (center) and milk (left), are a common bodybuilding supplement
An education campaign launched by the United States Department of Agriculture about 100 years ago, on cottage cheese as a lower-cost protein substitute for meat.
A child in Nigeria during the Biafra War with kwashiorkor – one of the three protein energy malnutrition ailments affecting over 10 million children in developing countries.
Image: Pesce al mercato 1
The calorie is a unit of energy that originated from the caloric theory of heat. The large calorie, food calorie, dietary calorie, or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter of water by one degree Celsius. The small calorie or gram calorie is defined as the amount of heat needed to cause the same increase in one milliliter of water. Thus, 1 large calorie is equal to 1000 small calories.
A 710-millilitre (24 US fl oz) energy drink with 330 large calories