In general, North Americans and most Europeans consume protein-rich diets, consisting of moderate to high levels of meat products, dairy and vegetable sources, such as soybeans. A protein-deficient diet is much more common in third-world countries, especially in developing children. However, low-protein diets are intentionally chosen by some vegetarians or recommended to those experiencing kidney or liver problems. Nevertheless, inadequate dietary protein has a variety of negative consequences.
Dietary Protein
Protein is reduced to amino acids during digestion, which are then used to build and repair various tissues, such as muscle and connective tissues. Protein is also required to maintain skin, hair and nails of the hands and feet. According to "Biochemical, Physiological and Molecular Aspects of Human Nutrition," a significant portion of the body consists of protein, at about 45 percent. Furthermore, amino acids are sometimes used as an energy source if carbohydrates and fats are depleted. The human body utilizes 20 amino acids, and nine must come from the diet because the body cannot synthesize or recombine them. Without any of these nine essential amino acids, symptoms of protein deficiency develop.
Recommended Protein Intake
Recommended daily intake of protein varies dramatically from person to person and depends on age, size, gender, physical activity and environment. According to "Advanced Nutrition and Human Metabolism," a general guideline is that at least 10 percent of consumed calories per day, and perhaps as high as 35 percent, should be from protein sources. For example, based on a daily average diet of 2,000 calories, between 50 and 175 g of protein should be consumed. Of course, the type of protein is very important too. Animal-based sources, such as meats and dairy products, often contain all the essential amino acids, but they are also high in saturated fats that increase the risk of cardiovascular diseases. Plant sources rarely contain harmful fats and are a great source of fiber, but they are incomplete sources of amino acids.
Severe Protein Deficiency
In third world countries, extreme lack of protein can occur, leading to diseases such as marasmus and kwashiorkor, according to "Human Biochemistry and Disease." Marasmus occurs in people who are starving from lack of calories and protein, which leads to dramatic weight loss, muscle wasting and immune deficiency. Kwashiorkor often occurs in young children who are fed carbohydrates, such as white rice, but little to no protein. Kwashiorkor results in fluid retention in the lower abdomen and face, muscle wasting and an enlarged liver.
More Common Protein Deficiency Symptoms
For Americans on very low protein diets, initial symptoms of deficiency usually include fatigue, emotional instability, reduced concentration and compromised immunity. Reduced immune response can present as more infections and cuts that take longer to heal. Later symptoms include loss of hair, brittle fingernails and muscle weakness, as protein is required to build and maintain muscle tissue. Advanced symptoms include respiratory problems, irregular heartbeat, osteoporosis, anemia and generalized edema. Edema, or fluid retention, is most common in the feet and ankles, although it can spread to the abdomen. Children who are affected by low protein diets often show signs of slow growth and development. Chronic low protein diets can lead to death eventually, usually from heart failure or respiratory infection, according to "Harrison's Principles of Internal Medicine."
References
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Advanced Nutrition and Human Metabolism (fifth edition)"; Sareen Gropper and Jack Smith; 2009
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Harrison's Principles of Internal Medicine"; Dr. Anthony Fauci et al; 2008
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