What are proteins?
Proteins are made from chains of amino acids – often called 'the building blocks of life'. There are a total of 20 amino acids that combine in different ways to form a variety of proteins that the body uses to create cells, hormones and enzymes. 11 of these 20 amino acids are manufactured in the body by the liver. The other 9, called "essential" amino acids, can only be obtained through diet.
When we eat foods that have proteins, the body breaks down the long chains of amino acids into single amino acids. The body's cells use these amino acids to manufacture new proteins which are used to repair tissues, make hormones / antibodies / enzymes, help balance acid-base, fluid and electrolytes, as well as providing some of the body's energy – explaining the term ' building blocks of life'.
Complete vs incomplete proteins
Amino acids are abundant in protein-based foods. A food is said to be a "complete" protein when it contains all of the nine essential amino acids we need. Most animal based protein foods such as eggs, meat, fish, poultry, cheese and milk are complete protein foods. Some soy products also contain the nine essential amino acids. Plant proteins such as grains, legumes, seeds and nuts are considered incomplete proteins, because they have low amounts or are missing one or more essential amino acids.
While individual plant based protein sources are often 'incomplete', a wide range of scientific studies and the official position of nutritionist authorities have shown that a vegetarian / vegan diet actually provides the entire range of amino acids required by the body. Since different vegetarian products have different levels of the 9 essential amino acids, a combination of various vegetarian foods can provide the body all the amino acids it requires.
For example, rice, beans, peanut butter and bread are all examples of 'incomplete' proteins. However, rice eaten with beans or a peanut butter sandwich are examples of a complete protein. It is not even critical to try and balance the amino acids in every meal. Studies have shown that a healthy vegetarian diet, provide more than required levels of all the essential amino acids required by our bodies.
This is why, a vegetarian diet provides 'complete proteins'.
Health issues due to too much protein (kidney diseases)
Most people would be surprised to learn that their protein needs are actually much less than what they have been consuming. The Recommended Dietary Allowance (RDA – as per Dietary Reference Index of Institute of Medicine, USA) for proteins for an average, sedentary adult is 0.8 grams per kilogram of body weight (translating to an average of 56 gm / day for males & 46 gm/day for females in the age group of 40-50 years). This level of protein intake is well supported by a vegetarian diet, as shown above. A typical non-vegetarian diet, in fact leads to an overconsumption of proteins by the body.
When people eat too much protein, their body absorbs more nitrogen than is needed. This excess nitrogen needs to be expelled by the body through urine, increasing the strain on the kidneys. The more protein that is consumed, the greater is the strain on the kidney to ensure that nitrogen is expelled from the system. Overtime, people who consume too much protein, risk permanent loss of kidney function.
Excess nitrogen in the system, also leads to the liver becoming overloaded allowing ammonia and other toxic substances to build up in the bloodstream. This can lead to hepatic encephalopathy – a condition marked by a decline in brain and nervous system function.
Health issues due to the acidic structure of animal proteins (Osteoporosis)\
Animal proteins are high in sulphur-containing amino acids, especially cysteine and methionine. Sulphur is converted to sulphate, which tends to acidify the blood. Diets that are rich in animal protein, tend to contain significantly higher levels of sulphur-containing amino acids than the more alkaline variety found in plant protein. The body responds to the blood acidity, by pulling calcium and other minerals out of the bones to form salt that neutralize the acid and send it out in the urine. The result in a leeching of calcium from the bones, adversely impacting bone mineral density and increasing the risks of fractures, osteoporosis and other bone related problems.
Various scientific studies have indicated that countries / people with higher levels of animal protein intake, actually suffer from higher rates of osteoporosis and fractures.