Dietary Protein and Body Protein 

Twenty different amino acids are used to build the hundreds of proteins that make up our bodies.

Where do these amino acids come from, and what are they?

We did not directly absorb the protein from the beef we ate last night into our muscles.

We first break down the proteins in the meals we ingest into tiny "peptides." Some of these peptides undergo further digestion to produce their amino acids. The small intestine only absorbs amino acids and short peptides into the bloodstream. After that, they are transported to the liver, muscles, brain, and other organs, where they are either transformed into other amino acids required by those organs or used to create new proteins.

Nine of the 20 amino acids that make up proteins are considered "essential" since our bodies cannot produce them, and we must consume them in our diet. The remaining 11 must be included since some are necessary for newborns and people with specific conditions. Because human bodies can produce them sufficiently, the remaining amino acids are considered "non-essential."

However, by eating a well-balanced diet that includes a range of foods, they can easily be satisfied. Protein is present in most foods. Some foods are superior to others as sources of protein. All essential amino acids must be present in "complete" proteins for our bodies to produce them. Fish, eggs, low-fat dairy products, lean meats and poultry, and low-fat dairy products are the finest sources of complete protein.

Although the grains and cereals group of foods, which forms the foundation of the Food Guide Pyramid, are good sources of protein, they are referred to as "incomplete" proteins because they frequently lack one or more essential amino acids. For instance, the necessary amino acids lysine and tryptophan are insufficiently present in the proteins of wheat and corn, respectively. Legumes, on the other hand, are often low in methionine but high in lysine. Soybeans are legumes with complete protein.

Does this imply that the only way to obtain all the amino acids you require is to consume animal products like meat, eggs, and dairy?

The opposite. You will probably receive all the amino acids required and in the right proportions by consuming various foods, such as grains and legumes. By consuming diverse combinations of plant proteins, such as beans, corn, rice, and other cereal grains, people from many cultures, including vegans (vegetarians who eat no foods of animal origin) can receive enough amounts and types of protein. Nutritionists now concur that these items can be consumed at different times throughout the day, even though it was traditionally believed that they needed to be consumed together at the same meal.

We obtain additional health advantages when we consume grains and legumes rather than foods of animal origin, which make up a more significant portion of the protein in our diets. Legumes and whole-grain diets contain vitamins, minerals, fiber, and other nutrients that promote health. If that does not seem like enough reason to switch, grains and legumes do not contain the high levels of saturated fat found in foods derived from animals, which, as you will discover later, are associated with several ailments.

Contrary to popular perception, consuming more dietary protein than is advised would not automatically lead to more significant muscles. Our bodies do not store protein surplus. The different amino acids are converted to fat and stored as fat if we consume more protein than our bodies require to replace the lost amino acids throughout the day. Like carbs, dietary protein contains roughly four calories of energy per gram. Our need for protein increases during periods of rapid growth since our requirements for protein mainly depend on the size of our bodies. As a result, the protein recommendations vary by age and are slightly greater for pregnant or nursing women than for other adults.

According to the required allowances, nearly all healthy individuals receive adequate protein. However, many people consume twice as much as this, frequently in the form of meat and dairy items that are heavy in saturated fat, raising the risk of coronary artery disease and various cancers.

What if we eat too little protein?

Only some people run the risk of consuming insufficient protein. Protein deficiencies, however, can occur in those with highly restricted diets, those who are unable to eat, and those whose needs are raised due to disease or trauma. The body of a protein-deficient person starts to rob protein from muscle by breaking down that protein to its constituent amino acids to replace the pools of necessary amino acids that have been depleted to manufacture essential proteins such as enzymes and hormones. Significant muscle protein losses can be catastrophic because muscle is necessary for many critical bodily processes (such as breathing through the diaphragm and our hearts pumping blood).

Fortunately, most people can quickly meet their protein needs by eating a balanced diet based on the Food Guide Pyramid, including those who engage in regular, demanding endurance activity.

Only nine of the 20 amino acids are considered "essential" in our diets because they must come from the foods we eat rather than being produced by our bodies.

Essential in our diets	Essential in our diets under  some circumstances	Non-essential in our diets
Histadine	Arginine	Alanine
Isoleucine	Cysteine*	Asparagine
Leucine	Tyrosine†	Aspartic acid
Lysine		Glycine
Methionine		Glutamine
Threonine		Glutamic acid
Tryptophan		Proline
Phenylalanine		Serine
Valine

 

*Cysteine can be synthesized from the essential amino acid methionine. †Tyrosine can be synthesized from phenylalanine when supplied in adequate amounts

 

Here you can find several examples of foods with essential amino acids.

Essential in our diets	Animal-based foods	Plant-based foods
Histidine	Meat, Fish, Poultry	Nuts, Seeds, Whole grains
Isoleucine	Meat, Fish, Egg, Poultry, Cheese	Lentils, Nuts, Seeds
Leucine	Dairy	Soy, Beans, Legumes
Lysine	Meat, egg	Soy, Black beans, Quinoa, Pumpkin seeds
Methionine	Egg	Grains, Nuts, Seeds
Threonine	Cottage cheese	Wheat germ
Tryptophan	Cheese, Chicken, Turkey	Wheat germ
Phenylalanine	Meat, Fish, Dairy, Poultry	Soy, Beans, Nuts
Valine	Cheese	Soy, Peanut, Mushrooms, Whole grains, Vegetables