protein

1. (biochemistry, countable) Any of numerous large, complex naturally-produced molecules composed of one or more long chains of amino acids, in which the amino acid groups are held together by peptide bonds.Examples: "Proteins carry out the bulk of cellular functions, including relaying signals, providing structural support, and accelerating biochemical reactions."; "Because of her significant testing, Avery had had DNA sequencing of her “exome,” the part of her genome that makes proteins in the body, said Dr. Michael Wangler, a researcher at the Jan and Dan Duncan Neurological Research Institute at Texas Children’s Hospital."countable

2. (nutrition, uncountable) One of three major classes of food or source of food energy (4 kcal/gram) abundant in animal-derived foods (meat) and some vegetables, such as legumes.Examples: "Along with carbohydrates and fat, protein is one of the three main macronutrients that make up our diet. Furthermore, it is the only macronutrient that supplies us with amino acids, making it essential for survival."uncountable

3. (nutrition, countable) A food rich in protein, often a meat or meat substitute.Examples: "The preparation style should be the same for both proteins so that the side dishes compliment the meal."; "Served with seasoned rice, classic Greek salad, pita, tzatziki, choice of 2 proteins & 2 sides"; "What should you get for lunch at a halal cart? Nutritionists explain how to pick a protein that isn't packed with calories and why you should beware the white sauce"countable