Carbohydrates, fats and proteins form a group of essential nutrients called macronutrients. The prefix "macro" indicates that you need these nutrients in large quantities, which is one of three factors these macronutrients have in common. Macronutrients also share a role in that all three provide calories for energy; additionally, they're all made from similar elements. However, the basic building blocks are different among the three macronutrients, and protein contains two elements unique to protein.
Proteins, carbohydrates and fats are made from three basic molecules: carbon, hydrogen and oxygen. However, all proteins contain an element not found in carbohydrates and fats -- nitrogen -- and some proteins also contain sulfur. These elements combine in varying amounts and shapes to form the basic building blocks of each macronutrient. The main unit that builds all carbohydrates is a monosaccharide, or sugar, while triglycerides make fats and proteins consist of amino acids. Sulfur is incorporated into some proteins through two amino acids: methionine and cysteine.
Macronutrient Building Blocks
Energy production is the primary duty of carbohydrates, but fats and proteins have other jobs to fill. Besides providing the body's second source of energy, fats cushion organs, maintain cell membranes and help you absorb vitamins A, D, E and K. Even though proteins can provide energy, your body prefers to use them for other essential jobs. Proteins build all of your tissues, including muscles and skin, and they produce substances you can't live without, such as hemoglobin and enzymes. In other words, proteins provide the building blocks for your body, according to the Merck Manual Home Health Handbook.
Amino Acids Fill Diverse Roles
During digestion, enzymes breakdown proteins into single amino acids, which are absorbed into your bloodstream. Then cells throughout your body use the amino acids to build whatever protein they happen to need. Individual amino acids also fill other roles. Some amino acids help build neurotransmitters. For example, tyrosine helps produce epinephrine and tryptophan is converted into the mood-regulating neurotransmitter serotonin. Your body also needs tyrosine to synthesize epinephrine and histidine participates in the production of red and white blood cells. Three amino acids, cysteine, glycine and glutamate, combine to form an antioxidant called glutathione.
Your body can make 11 of the 20 amino acids used to make proteins, but you need to get the rest through your diet. You will get all the essential amino acids if you consume the recommended amount of protein from a variety of protein-containing foods. The recommended dietary allowance for protein is 46 grams daily for women and 56 grams for men. As a general guideline, you can figure on getting about 25 grams of protein from 3 ounces of meat, poultry and fish, 8 grams from a cup of yogurt or milk and 6 ounces from an egg. One cup of beans provides about 15 grams of protein.
- University of New Mexico: Biological Macromolecules
- Journal of Nutrition: The Sulfur-Containing Amino Acids: An Overview
- University of Illinois at Urbana-Champaign: Macronutrients: The Importance of Carbohydrate, Protein, and Fat
- Merck Manual Home Health Handbook: Carbohydrates, Proteins and Fats
- Biochemistry: Amino Acids are Precursors of Many Biomolecules
- World of Molecules: Histidine
- Institute of Medicine: Dietary Reference Intakes: Macronutrients
- National Academies Press: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients)