11.3: Protein Deficiency

Protein deficiency is common in populations that don’t have rich sources of protein (e.g.,meat, eggs, legumes). When there are only very dilute sources of protein, it can be hard to get enough, even if there’s plenty of food. Diets that consist entirely of low-protein plant foods can meet calorie needs without meeting protein needs.

Protein and calorie deficiencies commonly occur together. Without enough calories, amino acids are used for energy instead of being used to make protein. When adults are protein deficient, they look emaciated from a loss of body tissue—there isn’t enough protein to maintain it. Protein deficiency is much more serious in children.

The most striking result in young children is impaired growth. There isn’t enough protein to sustain growth, and children don’t grow to their genetic potential. Because bigger bodies need more protein, stunted growth is a form of environmental adaptation—smaller people need less protein (and fewer calories).

If the diet improves dramatically (e.g., moving to a higher-income country), the next generation often grows dramatically taller—an adaptation to a more bountiful environment.

Severe protein deficiency hampers the synthesis of a wide variety of proteins. For example, less albumin (a protein in blood-plasma; Chap. 7) is made. Albumin holds water (like all our proteins) and is important in fluid balance. When albumin is too low, some of the fluid normally held in plasma by albumin, flows out of blood vessels into surrounding tissue. As a result, the tissue swells (edema), and the child looks “puffy,” especially in the face and belly.

The children also tend to be anemic (hemoglobin is a protein) and prone to infection (antibodies are protein). If their hair is normally black, it may have light bands of orange, because they can’t make enough pigment to darken it (the pigment melanin is made from the amino acid tyrosine). Brain growth is also hampered, often starting before birth with a malnourished mother. To make matters worse, protein-calorie malnutrition is often complicated by other nutrient deficiencies and by infectious diseases.

Breast-feeding is extremely important in developing countries where malnutrition and poor sanitation are common. Breast milk often is the only regular source of high-quality protein (and other essential nutrients) available to an infant. Infants often develop protein-calorie malnutrition when displaced at the breast by a newborn sibling. When a nursing mother is malnourished, she makes less milk, but the milk she does make is fairly normal in composition.

Aggressive marketing of infant formula in developing countries has come under attack for good reason. Mothers everywhere want their children to be as healthy and happy as those pictured in the ads. When poverty-stricken mothers are given free samples of infant formula, they can’t afford to buy more. Meanwhile, if they stopped breast-feeding while using the free samples, their milk production may have stopped.

To make matters worse, the mothers often greatly over-dilute the formula (thus diluting the nutrients) to make it go further. Unsanitary water added to the formula can cause diarrhea, a major cause of infant death in these countries. Sometimes, when the formula is gone (or there was none to begin with), liquids of poor nutritional quality that look like milk (e.g., rice water) are used in the baby bottle. World health organizations are doing what they can to encourage breast-feeding in low-income countries.