Proteins… Quality, functions and requirements

Proteins are specialized substances, made up of amino acids, whose functions cannot be performed by other types of nutrients in our body.

Protein functions

    • Plastic, structural or construction: They are part of the body’s structures, supplying the material necessary for the growth and repair of body tissues and organs.

    • Regulatory: Some proteins collaborate in the regulation of cell activity. Certain hormones are of protein nature (insulin, growth hormone…), many enzymes are proteins that promote multiple organic reactions and some neurotransmitters have amino acid structure or are derived from amino acids and regulate the transmission of nerve impulses.

    • Defensive: They are part of the body’s immune system or defenses (antibodies, immunoglobulins).

    • Involved in coagulation processes: Fibrinogen, thrombin …. prevent blood loss when a blood vessel is damaged.

    • Transport of substances: They transport fats (apoproteins), oxygen (hemoglobin), and also facilitate the entry into cells (membrane transporters) of substances such as glucose, amino acids, etc.

    • Energetic: when the contribution of carbohydrates and fats is insufficient to cover energy needs, amino acids from proteins are used as energy fuel (1 gram of protein supplies 4 Kcal).

In order to meet protein demands, it is necessary that protein intake meets two requirements
protein intake must meet two requirements:

    1. Should be sufficient

    1. It should be of high quality.

How much protein do we need?

The recommended dietary allowance (RDA) for protein is 0.8g/kg/day in adults. However, this amount varies depending on the state of health. In the presence of old age, illness or both, protein requirements are elevated, making it necessary to increase the intake of high quality protein.

Let’s take a look at some conditions and their requirements:

Protein requirements in older adults:

Throughout the aging process, individuals undergo physiological changes, medical conditions, psychological and social factors, which cause significant alterations in body composition, functional capacity and various physiological functions that contribute to the development of sarcopenia.

The loss of strength and muscle mass characteristic of sarcopenia leads to dependence and potential disability. By age 80, the reduction in muscle tissue is 50% and this loss of lean mass can be with or without adipose tissue wasting, even with an adequate diet.

Protein malnutrition results in increased frailty, decreased healing and impaired immune function.

The PROT-AGE study developed in 2013 by the European Union Society of Geriatric Medicine with cooperation from other scientific organizations recommends intakes between 1 to 1.5 grams per kilogram of body weight in older adults with or without disease. These intakes have been shown to counteract the chronic loss of muscle mass associated with the aging process. Other physiological processes that may benefit are: bone health, maintenance of energy balance, cardiovascular function and healing.

Oncology patients:

Protein intake is essential during all stages of cancer treatment for tissue regeneration and immune system strengthening, recovery and long-term survival.

The recommended daily protein intake ranges from 1.2 to 2 per kilogram per day in order to achieve a positive nitrogen balance and ensure adequate utilization of protein in sufficient quantities for maintenance and protein synthesis.

Oncologic patients have periods of inappetence, so small and frequent portions are suggested. Likewise, when there are swallowing problems due to oral or esophageal candidiasis, the use of protein supplements has been recommended because they can be easily ingested allowing to reach the requirements without increasing the amount of food consumed.

HIV patients:

The prevalence of malnutrition in HIV patients is one third in those in the asymptomatic phase and is usually aggravated in the symptomatic and terminal phase of the disease.

There are three factors responsible for malnutrition, which are listed below:

    • First, there is anorexia, which is a consequence of the inflammatory state, inappetence due to opportunistic infections in the esophagus and mouth or adverse effects of medications such as nausea and/or depression.

    • Secondly, deficient absorption of nutrients caused by damage to the intestinal cells, mainly due to flattening of the microvilli.

    • Third and finally, the increased inflammatory response and multiple opportunistic infections increase resting metabolic expenditure by 10 to 30%.

All this results in muscle hypercatabolism and increased acute phase protein synthesis resulting in protein malnutrition with loss of lean mass.

In HIV patients, poor nutritional status and loss of lean mass is associated with increased mortality rates.

The recommended daily protein intake varies between 1.2 to 1.5 grams per kilogram of body weight depending on the stage of the individual. If the patient is stable, 1.2 grams per kilogram is necessary and during acute illnesses it is suggested to increase the consumption up to 1.5 grams per kilogram.

Adequate protein intake has been shown to prevent further muscle loss, maintain lean mass and strengthen the immune system, all of which reduce complications from opportunistic infections and improve quality of life.

Patients with bariatric and metabolic surgery:

In order to reduce abdominal fat, operative time, surgical complications and to achieve a greater postoperative weight loss, a hypocaloric diet of less than 800 calories with an adequate intake of protein, vitamins and minerals is recommended 10 to 15 days before surgery. It is usual to prescribe liquid diets to facilitate compliance with nutritional goals, and the use of protein modules in order to ensure optimal intake of this nutrient without increasing fat or carbohydrate intake.

After surgery, protein is essential to promote healing. In addition, the anatomical and physiological modifications of the gastrointestinal tract that occur after the surgical procedure generate nutritional alterations and deficiencies that must be treated in a timely manner.

In gastric restriction, the reduced volume of the reservoir, between 30 and 60 milliliters, limits the amount of food ingested and causes intolerance to protein sources such as meat, milk and its derivatives.

In a study developed by Andreu and collaborators, 4 months after bariatric surgery, 45% of the participants did not tolerate more than 60 grams per day of protein from food. Evidence has shown that protein intake can be deficient even up to the first year after surgery.

Protein deficiency is usually assessed by the appearance of different signs and symptoms. The most common clinical manifestations range from hair loss, fatigue, muscle pain to, in more severe cases, edema due to hypoalbuminemia.

The recommended daily intake varies between 60 and 120 grams of protein, administered in amounts between 20 to 30 grams per intake, 3 to 4 times a day.

What about protein quality?

There are different ways to measure the quality of a protein. In this article we will consider two indicators:

    1. How much of what I consume is digested (digestibility).

    1. How much of what I digest is utilized or retained by the body (Net Protein Utilization).

During the digestion and absorption processes, different factors affect the capacity of enzymes to digest food, or limit the absorption of nutrients; in other words, not all the protein ingested is absorbed.

In relation to digestibility determined in ileum, whey protein isolate has the highest score, 99%, meaning that its amino acids are better absorbed in relation to other proteins such as casein which has between 94 and 95% and soy protein with 92 to 98%.

Once the amino acids are absorbed and enter the circulation, they must be utilized. Net protein utilization (NPU) is higher in whey protein isolate (92%) than in casein (72%) or soy protein isolate (61%).




     Soy Isolate













Taken from Castellanos et al (2006), Damodaran S et al (2008).

Nutrisite® Protein is a protein module based on 90% Whey Protein Isolate. It is included in the MIPRES tables and indicated in the nutritional treatment of people with increased protein needs such as the elderly, people with debilitating diseases such as cancer, HIV, COPD, chronic renal insufficiency, pre and post operative, bariatric surgery… Read more