Protein functions in the body: why do we need proteins?

Proteins are major structural and functional components of human body

  • Structurally, Collagen and elastin are critical components of connective tissue such as cartilage, actin and myosin are major components of muscles and keratin is major component of hair
  • Functionally:
    • Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism
    • Several important peptide hormones are secreted in the body and regulate important functions, some examples include
    • Growth hormone,
    • Adrenocorticotropic hormone (ACTH), which regulates the secretion of glucocorticoids,
    • Insulin which regulates carbohydrate metabolism and
    • Hormones of  gastrointestinal tract (cholecystokinin, gastrin), and
    • Of fat tissue stores (leptin)

Protein metabolism: what happens to proteins eaten in the food?

  • The dietary protein is broken down into amino acids, which include essential amino acids, amino acids which can’t be made by the body and non essential amino acids which the body can make from components: of the total 22 types of amino acids nine are ‘essential amino acids’, these can not be synthesized by the body, whereas the other amino acids can be made by the body as per need
  • The amount of amino acids needed for repair and growth functions are taken up by the body
  • Rest of the amino acids are broken down into two parts:
    • one containing nitrogen, which is converted into a safe form (ammonia to urea) and excreted and
    • another part containing what is called the carbon-skeleton is redirected mostly into the fat metabolism, so IF there is calorie surplus, this part is converted into fat and stored by the body
    • However, if you increase the protein content in your diet without overloading calories (by substituting carbs or fat with protein), the body uses this protein to produce calories (by a process called gluconeogenesis) and thus the carbon skeletons are not converted into fat but used up

Protein requirement /day in food: how much do we need?

The minimum requirement for protein is defined as .8-1 gm/kg (body weight). A least 10% of total calories in food should come from protein. On the other hand, protein should not provide more than  30-35% of total calories.

Indian diets typically give less than 15% calories from protein.  In fact, a big number of Indians get even less than 10% of total calories from food because of our less protein dense staple protein foods (dal or pulses)

Can we safely up our protein uptake as much as we like?

The answer is yes, to a very large extent!

Some health problems may result if a high-protein diet (proteins higher than 30% of total calories)  is followed for an extended time (Indians hardly ever manage more than 20% of total calories by protein intake) :

  • Animal sources of protein may increase your risk of heart disease
  • Some high-protein diets restrict carbohydrate intake so much that they can result in nutritional deficiencies
  • A high-protein diet may worsen kidney function in people with advanced kidney disease

Protein quality: what are ‘best’ proteins?

What are ‘good’ or ’complete proteins’? Are proteins of vegetable sources ‘incomplete’ and therefore could vegetarians have deficiencies of essential amino acids?

Proteins used to be graded on the basis of their amino acid constitution. The ones that provided all or nearly all amino acids were considered complete and had high scores (Biological Value, PDCAAS etc.). Proteins from plant sources often lack one or more amino acids (e.g.. lysine in most grains) and thus have low biological value or PDCAAS. They were considered inferior to animal proteins in the past.

But the importance given to BV or PDCAAS has gone down in recent times. This is because people often eat various food stuff together and thus compensate for deficiencies. Vegetarians also will have no problem ensuring that they get all essential amino acids in diet, if they consume protein from various sources (grains, dals/beans, milk etc.)

Good protein choices include

  1. Dals, beans and soy protein (tofu, soy nuggets)
  2. Fish, skinless poultry, goat meat or mutton, lean beef, lamb or pork and eggs
  3. Low-fat dairy products

The protein foods to consume in moderation are

  1. Processed meats
  2. Full fat red meat: lamb, beef and pork and organ meats such as liver
  3. Full fat milk
  4. Nuts: too many can call calorie overload

To know more about choosing the right proteins, go to ‘Tips for making healthy protein choices

CHECK OUT: Our references for recommendations on diet