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Proteins

Proteins are nutrients that aid in the growth of an individual. Their functions can be summed as the generation and regeneration of human tissues, the production of metabolic enzymes, the production of certain hormones such as thyroxine and insulin¹ and providing energy to the body to the tune of 4 food calories per gram.

Proteins are a chain of amino acids, and are broken down to their constituent amino acids during digestion. These amino acids are transported by the blood to various parts of the body to refuel the cells for their lost protein (cells use protein for aforementioned functioning). This process of refuelling or balancing proteins inside the cells is called protein synthesis.

There are 20 amino acids² required for the human body, of which 5 are synthesised by the human body, 6 are conditionally essential and 9 are essential³ and must be procured from diet. Most scientists consider conditionally essential amino acids as non-essential amino acids; thus raising their number from 5 to 11.

• Essential — Threonine, Valine, Leucine, Isoleucine, Methionine, Phenylalanine, Tryptophan, Lysine and Histidine.
• Non-essential — Arginine, Alanine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, Serine and Tyrosine.

The quality of protein we consume is determined by the number of essential amino acids present in it (called the amino acid profile) and the protein's digestibility. Proteins containing all the essential amino acids are called complete proteins, and proteins lacking them or containing them in trace amounts are called incomplete proteins.

It is important that human diet contain non-essential amino acids since they can reduce the use of essential amino acids for biological functioning that can be carried out by non-essential amino acids and for the synthesis of non-essential amino acids⁴.

Animal and plant based protein

Proteins can be sourced from both plants and animals. Plant sources include spirulina, beans, lentils, mushrooms, hemp seeds, etc. Animal sources include fish, meat and eggs.

There is a lot of misinformation with respect to animal based and plant based protein. One of the misconceptions is that proteins from meat are superior to proteins from plants. In nutrition science, the superiority or quality of protein is judged based on its ability to get digested and the amino acid profile present in it. Below is a table listing⁵ the protein digestibility of food providing complete protein.

From this table we can infer the following.

• Among complete proteins, animal based protein has better digestibility than plant protein; however the difference is of no significance since it is within a 10% range. Also, protein digestibility estimated in studies may not be the actual number in real life because of the changes in conditions.
• While the difference in protein digestibility of animal based and plant based proteins is narrow, the difference between meat based and non-meat based proteins is narrower. This is because of the contribution of egg to the non-meat based set.
• Add to this the fact that meat contains unhealthy nutrients such as cholesterol and bad fats, and you can conclude that plant based protein is healthier. The nutritional benefit of a food is a function of multiple nutrients and physiological state of the person.

The claim that "enough" protein can only be sourced from animal sources is also false. "Enough" can be fulfilled by eating more. But in the case of plant based protein, this isn't required because most plant based protein sources such as lentils and nuts equal the amounts of protein in meat per 100 grams. Spirulina has twice the amount of protein than lean meat per 100 grams⁶.

The take away is that if you decide to go vegetarian, there is no reason not to. If you do not have constant access to plant based complete protein sources, a combination of plant based incomplete protein sources can provide you the complete protein spectrum because no essential amino acid is absent from all sources. In short, variety of food and following a cuisine will take care of your protein requirement.

Protein requirements

Protein requirements are depended on various factors. The general recommended amount for adults is 1g/kg/day while the Indian Council of Medical Research and National Institute of Nutrition recommends .83g/kg/day⁷.

Here is a table with the Recommended Daily Allowance (RDA) and how much you should consume. The disparity between the two quantities is because of protein digestibility. For instance, if your body requires 10 grams of protein, you should consume more than 10 grams of protein since a small percentage is not digested.

An important observation from a study is that in a healthy body "when protein intake is low, dietary protein is used more efficiently, urea nitrogen excretion is reduced, and amino acid synthesis pathways are stimulated"⁴. Therefore, it is possible to "adapt" to a low protein intake, or receive enough proteins from a low protein intake if you are a healthy individual. If, on the other hand, you have infections, diarrhoeal disease, wounds or burns, a low protein intake will not be efficiently used giving rise to protein deficiency.

Protein deficiency

As a growth and repair nutrient, protein deficiency stalls the generation and regeneration of human tissues. As a raw material for the production of enzymes and hormones, protein deficiency can shut off certain biological functioning.

Protein deficiency causes psychological and physiological conditions such as intellectual under-development and Kwashiorkor. However, the impact of protein deficiency differs as per the life stage of an individual — fetus, infancy, childhood, adulthood and old age.

Protein surplus

Anything more is useless. Amino acids consumed in excess of the body's needs as stated in the beginning are degraded by transaminations, deamination, and urea formation (the nitrogen is excreted and the carbon skeleton is recycled as a carbohydrate or fat). It is estimated that the body degrades and resynthesises more amino acids in a day than are consumed through the diet⁴.

Excess of protein is not particularly known to create any health conditions. However, let that not be a license to voraciously consume high protein diet for two reasons.

1. Any imbalance in the amino acid profile; ie, if any one essential amino acid is present in high amounts, it automatically creates a deficiency of other amino acids even if they are in required amounts⁴ because the body fails to use them. Almost the same effect can be found with vitamins: an increase in any amino acid will increase the deficiency of certain B vitamins.
2. Since the body still engages in degrading and deanimating the unwanted proteins. It is an unnecessary load to the system.

Everyday calculations

Since we do not generally consume food by precise measurements of weight and calories, we need an acceptable practical method to judge the surplus and deficiency of our nutrients. This section aims to act as a guide.

If you lack enough flesh (not fats) in your body, it is a sign that you lack protein. If you see issues with your skin, hair and nails, it may be due to protein deficiency. If you often fall sick, feels fatigue, weak and hungry, chances are that you do not consume enough carbohydrates and proteins.

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