6.5: Diseases Involving Proteins
- Page ID
- 21139
Learning Objectives
- Identify the potential health risks associated with low and high protein intakes.
As you may recall, moderation refers to having the proper amount of a nutrient—having neither too little nor too much. A healthy diet incorporates all nutrients in moderation. Low protein intake has several health consequences, and a severe lack of protein in the diet eventually causes death. Although severe protein deficiency is a rare occurrence in children and adults in the United States, it is estimated that more than half of the elderly in nursing homes are protein-deficient. The Acceptable Macronutrient Distribution Range (AMDR) for protein for adults is 10-35% of calories, which is a fairly wide range. In this section we will discuss the health consequences of protein intake that is either too low to support life’s processes or too high, thereby increasing the risk of chronic disease.
Health Consequences of Protein Deficiency
Although severe protein deficiency is rare in the developed world, it is a leading cause of death in children in many poor, underdeveloped countries. There are two main syndromes associated with protein deficiencies: Kwashiorkor and Marasmus.
Kwashiorkor
The name Kwashiorkor comes from a language in Ghana and means, “the sickness the child gets when the new baby comes". The syndrome was named because it occurred most commonly in young children (1-3 years of age) who no longer drink breast milk, usually because another child had just been born. Subsequently the child was fed watery porridge made from low-protein grains, which accounts for the low protein intake. Consequences of kwashiorkor (Figure \(\PageIndex{1}\)) include:
- weight loss and muscle wasting, with some body fat retention
- retarded growth and development (less severe than with marasmus)
- swelling (edema), which results in extreme belly distention
- enlarged, fatty liver
- loss of appetite, sadness, irritability, apathy
- development of skin sores
- dry, brittle hair
Recall that one of protein’s functional roles in the body is fluid balance. Diets extremely low in protein do not provide enough amino acids for the synthesis of albumin. One of the functions of albumin is to hold water in the blood vessels, so having lower concentrations of blood albumin results in water moving out of the blood vessels and into tissues, causing swelling (edema). The primary symptoms of Kwashiorkor include not only swelling, but also diarrhea, fatigue, peeling skin, and irritability. Severe protein deficiency, in addition to other micronutrient deficiencies (such as folate, iodine, iron, and vitamin C), all contribute to the many health manifestations of this syndrome.
Marasmus
In addition to not getting enough protein, people with marasmus also don't get enough calories in their diet. Without enough protein or calories, people with marasmus also don't get enough of several other nutrients. Marasmus affects mostly children below the age of one in poor countries. Body weights of children with Marasmus may be up to 80% less than that of a normal child of the same age. Marasmus is a Greek word, meaning “starvation.” Consequences of marasmus include:
- wasting and weakening of muscles, including the heart muscle
- stunted brain development and learning impairment
- depressed metabolism and little insulation from body fat, causing a dangerously low body temperature
- stunted physical growth and development
- poor skin health
- deterioration of the intestinal lining, which further inhibits absorption of nutrients
- anemia
- severely weakened immune system
- fluid and electrolyte imbalances
Health Consequences of Too Much Protein in the Diet
The effects of high protein intakes on health is unclear. In the past, some research has linked high protein intakes with bone loss, kidney disease, and heart disease. High protein diets can increase calcium excretion, but current evidence does not support the idea that high protein diets lead to bone loss. In fact, recent systematic reviews on the topic showed no adverse effect of higher protein intakes on bone health and indicated some evidence in support of high protein intakes on bone density.1,2 However, these reviews also stated that additional research is needed to come to any conclusions about the association between high protein diets and bone loss. High protein diets appear to only increase the progression of kidney disease in people who already have kidney disease, and not to cause these problems. High protein diets that contain a lot of animal protein have been associated with heart disease and high blood cholesterol levels. However, diets that include lots of red meat are also high in saturated fat and cholesterol and sometimes linked to unhealthy lifestyles, so it is difficult to conclude that the high protein content is the culprit.
As with any nutrient, protein must be eaten in proper amounts. Moderation and variety are key strategies to achieving a healthy diet and need to be considered when optimizing protein intake. While the scientific community continues its debate about the particulars regarding the health consequences of too much protein in the diet, nutrition experts recommend having a moderate amount of protein in the diet and varying the sources of protein to include plant-based protein sources.
Key Takeaways
- Protein deficiency can cause swelling, fatigue, skin problems, irritability, muscle wasting, and eventual death from infection.
- The long-term health consequences of high-protein diets have not been adequately studied.
References
- Shams-White MM, Chung M, Du M, et al. Dietary protein and bone health: a systematic review and meta-analysis from the National Osteoporosis Foundation. Am J Clin Nutr. 2017;105(6):1528-1543. doi:10.3945/ajcn.116.145110.
- Groenendijk I, den Boeft L, van Loon LJC, de Groot LCPGM. High Versus low Dietary Protein Intake and Bone Health in Older Adults: a Systematic Review and Meta-Analysis. Comput Struct Biotechnol J. 2019;17:1101-1112. Published 2019 Jul 22. doi:10.1016/j.csbj.2019.07.005.