Fundamentals of Human Nutrition/Proteins and Health
Section 5.6 Proteins and Health[edit | edit source]
Proteins provide many health benefits to the human body, such as their participation in blood clotting, vision, making compounds, and energy. Proper blood clotting is necessary for healing injuries. The body uses proteins to make fibrin, which forms a tough clot on the injured tissue. Then, the body replaces fibrin with the protein collagen, which results in the development of a scar and a healed wound (Whitney, Rolfes, 2016). Also, proteins are essential components in vision. The protein opsin is responsible for sending nerve impulses to the brain to start the sense of sight (Whitney, Rolfes, 2016). Furthermore, proteins are made of amino acids, which the body can use to make other compounds that are essential for normal body functions. For example, the amino acid tyrosine is used by the body to make norepinephrine and epinephrine, which are both neurotransmitters (Whitney, Rolfes, 2016). In addition, the amino acid tyrosine is also used by the body to make thyroxine, which is a hormone that participates in metabolism. Similarly, when the body does not have enough carbohydrates or fats for energy, the body breaks down proteins to release amino acids and use them for energy or to make glucose (Whitney, Rolfes, 2016).
The types and amounts of proteins consumed influences their effect on human health. There are two types of proteins, animal proteins and vegetable proteins (Yasumoto, 1993). Animal proteins are associated with a high content of saturated fat, especially red meats, and products derived from milk (Yasumoto, 1993). High intakes of saturated fats increase the risk of developing heart diseases and becoming overweight. On the other hand, vegetable proteins are associated with a low content of saturated fat, especially nuts and legumes. Vegetable proteins help balance the lipid content in the blood and stabilize blood pressure, which as a result decreases the risk of developing heart diseases and becoming overweight (Yasumoto, 1993). Moreover, excessive intakes of proteins promote the development of osteoporosis and increases the risk of becoming overweight. Proteins and calcium are important for increasing bone density and keeping bones healthy. High intakes of proteins cause the body to excrete calcium from the body’s reserves (Symposium, 2009). When calcium levels are too low it causes bone loss, also called osteoporosis (Symposium, 2009). In addition, high intakes of proteins results in the body storing half of the excess kilocalories as body fat, which causes a gain in body tissue and increasing the risk of becoming overweight (Symposium, 2009). A low protein intake is associated with just a small increase in body tissue and no risk of becoming overweight. High proteins intakes are detrimental for people suffering from chronic kidney diseases, since excess protein cause the kidneys to overwork and as a result deteriorate the kidneys at a faster pace. Furthermore, there are some amino acids found in proteins that can have adverse effects on human health, such as homocysteine. High levels of homocysteine contribute to the development of heart diseases by increasing inflammation and the amount of oxidation in the body (Whitney, Rolfes, 2016). Also, there are some amino acids found in proteins that confer health benefits to the human body, such as arginine. Arginine helps lower the amount of homocysteine in the body and stabilize blood pressure, which as a result decreases the risks of developing heart diseases (Whitney, Rolfes, 2016).
5.6.1 Protein Insufficiency[edit | edit source]
Protein insufficiency can occur when an individual’s diet does not include enough protein or its monomer amino acids (Whitney & Rolfes, 2016). A stipulation is that this is a sustained deficiency in protein rather than a one time or by-chance occurrence. Whitney and Rolfes, in 2016, stated that such an insufficiency may result in long-term degradation of one’s own body proteins to make up for the lack of amino acids. They coined this condition as “protein-energy malnutrition,” a health event that is normally accompanied by a slew of other deficiencies (Whitney & Rolfes, 2016). While this condition seems harsh, its prevalence in developed nations, especially the United States, is limited due to the makeup of developed nations’ diets; many citizens of these states have high protein diets (Whitney & Rolfes, 2016).
According to Whitney and Rolfes in 2016, the recommended ratio of calcium to protein (milligrams to grams) is 20 to 1. As stated in the previous paragraph, the intake of protein is high in developed nations and this ratio is normally lower than recommended. Calcium and protein are vital to bone development, so a protein deficiency will lead to bones prone to injury and disease (Cao & Nielsen, 2010). Eventually osteoporosis can develop in the elderly or in teenagers, who have a negative caloric energy imbalance; treating patients with osteoporosis may include adding protein to their diet in order to “improve bone mineral density” (Whitney & Rolfes, 2016).
The variety of proteins incorporated into an individual’s diet may also affect weight gain or loss (Bujnowski et al., 2011). Bujnowski, in 2011, claimed that a diet insufficient in protein from vegetables and excessive in protein from animal products could result in weight gain. The opposite conditions (when the mass of vegetable protein intake exceeded the mass of animal-product protein intake) yielded the same results. Although Bujnowski’s conclusions were drawn from participants with a positive caloric balance, the weight gain was less in participants whose source of protein was mainly vegetable based than in participants whose source of protein was mainly animal-product based. Specifically, the animal-based protein eaters kcal surplus went towards more fat storage and less lean body tissue.
While Kwashiorkor is normally related to general malnutrition, protein deficiencies are a confounding cause of this disease (Kwashiorkor, n.d.). When the diet is adjusted to normal levels of carbohydrates and fats for energy levels, protein intake is necessary for rebuilding of important body structures lost due to protein-energy malnutrition.
5.6.2 Protein Excess[edit | edit source]
Protein is an abundant macronutrient which makes excessive intake a prevalent issue in many developed countries such as the United States of America, even though no Upper Limit has established due to minimal evidence (Whitney & Rolfes, 2016). Excess protein is linked to heart disease because food sources that are rich in proteins from animals tend to have high levels of saturated fat. Increasing amounts of protein obtained from nuts and legumes, which are plant sources, and reducing amount of protein obtained from animal sources can decrease the risk for heart disease at the hand of protein excess. There are some studies that suggest elevated homocysteine levels as a result of high saturated fat intake, among other things, can cause an increase is risk of developing heart disease (Whitney & Rolfes, 2016). Cancer is not caused by protein in itself but by foods that contain significant amounts of protein. Excessive intake of red and processed meats is linked to colon, pancreatic, and ovarian cancer (Whitney & Rolfes, 2016). Osteoporosis is also associated with excess protein because high protein intake causes an increase in the excretion of calcium. Increase in protein leads to increase in urinary calcium which can lead to negative calcium balance, calcium loss, and reduced bone mass (Heany & Layman, 2008). If protein intake is not proportional to calcium intake excess protein diminishes the amount of calcium in the bones. However, it is also possible that this osteoporosis may be the result of a calcium deficiency rather than an excess of protein or it may be a combination of both factors. Diets that are high in protein from animal sources are positively correlated to overweight and obesity. A study done to prove this theory found that people who ate 1,000 more calories than their recommended intake gained weight and those who consumed a high protein diet gained twice as much weight as those who consumed a low protein diet (Whitney & Rolfes, 2016). Protein excess is related to the function and health of the kidneys. The products of protein metabolism are successfully excreted when fluid intake is sufficient and the kidneys are working properly. Consuming large quantities of protein requires more metabolism which causes the kidneys to work harder to excrete the end products from that metabolism (Whitney & Rolfes, 2016). There is also evidence that excess amounts of protein can cause more rapid deterioration of kidneys due to hyperfiltration and an increase in glomerular pressure, although this has only been proven in situations where the kidneys are already under stress by pre-existing chronic kidney disease (Martin, Armstrong, & Rodriguez, 2005).
References: Heany, R., & Layman, D. (2008). Amount and Type of Protein Influences Bone Health. The American Journal of Clinical Nutrition, 87. Retrieved from: http://ajcn.nutrition.org/content/87/5/1567S.full Martin, W.F., Armstrong, L.E., & Rodriguez, N.R. (2005). Dietary Protein Intake and Renal Function. Biomed Central. Retrieved from: http://nutritionandmetabolism.biomedcentral.com/articles/10.1186/1743-7075-2-25 Whitney, E.N., & Rolfes, S.R. (2016) Understanding Nutrition: 14th Edition. Stamford, CT: Cengage Learning
5.6.3 Protein Functions on Health[edit | edit source]
Proteins are made up of chains of 20 different kinds of amino acids and amino acids are divided into essential amino acids and non-essential amino acids. Essential amino acids are amino acids the human body cannot synthesize on its own, and thus needs to be supplied in the diet. On the other hand, Non-essential amino acids are amino acids the human body can synthesize on its own with carbon, oxygen, nitrogen, and hydrogen in the diet. Amino acid being the base for protein creates protein that functions as the building blocks for growth, skin, muscle, bone, cartilage and many more. Protein is needed for body development, replenishment of blood lost, replacement of dead cells, and healing of scars and wounds. Additionally, proteins in forms of hormones, enzymes, and antibodies acts to promote healthy metabolic and immune processes. Furthermore, when fat and carbohydrate levels are low in the body, protein are degraded to generate energy for the body. Excess or deficient intake of protein alters the basic compound of the body and ultimately affects health.
5.6.4 Recommendations for Protein[edit | edit source]
Protein, fat and carbohydrates are macronutrients in which the body needs large amount of, however, unlike fat and carbohydrate, the body does not store protein. As a result, protein deficiency can impair body function and protein in excess can also have effects on health. Thus, the daily recommended intake of protein for adults is 0.8 grams per kilogram of body weight (Protein, 2015). The American diets usually acquire more than adequate amounts of protein and additional protein or amino acid supplements are not needed for healthy people.
5.6.5 High Protein Intake[edit | edit source]
High protein diets can skew the nutritional intake values towards a higher-than-recommended amount of fat, saturated fat, and cholesterol fat. Additionally, high protein diets can lower the recommended intake of fiber. The Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association states, “High-protein diets are not recommended because they restrict healthful foods that provide essential nutrients and do not provide the variety of foods needed to adequately meet nutritional needs. Individuals who follow these diets are therefore at risk for compromised vitamin and mineral intake, as well as potential cardiac, renal, bone, and liver abnormalities overall” (Jeor ST, Howard BV & Prewitt TE, 2001). High protein diets can lead to weight loss and diabetes due to a change of metabolism in which fat instead of carbohydrate are burn for fuel. Furthermore, high protein diets can also result in excess calcium excrete in urine and excessive calcium loss could result in osteoporosis (Osterweil N, 2005). Several health concerns associated with high protein diets are constipation, loss of energy, bad breath, kidney problems, difficulty concentrating, cardiovascular disease, gout, gallbladder problem, osteoporosis, diabetes, and cancer diagnoses (Physicians Committee, 2004).
Jeor ST, Howard BV & Prewitt TE. (2001). Dietary protein and weight reduction. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11591629
Osterweil N. (2005). The Benefits of Protein. Retrieved from http://www.webmd.com/men/features/benefits-protein
Physicians Committee. (2004). Health Problems Associated with High-Protein. Retrieved from http://www.pcrm.org/health/reports/analysis-of-health-problems-associated-with-high
Protein. (2015). Retrieved from http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/