Chapter 6

What are the possible long-term effects of an inadequate intake of dietary protein among children between the ages of 6 months and 4 years?

stunting of overall growth and an increased risk of infections.

Which eight foods are the major sources of proteins that cause food allergies?

The eight leading food allergens in the United States are milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, and soy.

Outline the major differences between kwashiorkor and marasmus

Kwashiorkor and marasmus are two types of undernutrition that are prevalent among children in developing countries. Kwashiorkor results primarily from inadequate protein intake. With kwashiorkor, the child is getting some food, but the food provides insufficient protein in relation to needs. The child experiences edema with maintenance of some subcutaneous fat tissue. Marasmus results primarily from extreme starvation—a deficiency of both protein and total calories. With marasmus, the child receives hardly any food at all and appears as skin and bones with little or no subcutaneous fat tissue.

Discuss the relative importance of essential and nonessential amino acids in the diet. Why is it important for essential amino acids lost from the body to be replaced in the diet?

Amino acids are the basic building blocks of protein, and the body needs 20 common types to function. Eleven of the amino acids are nonessential, meaning that they can be synthesized in the body if the right ingredients are present. The remaining nine are essential. They must be consumed in the diet because the body cannot synthesize enough of them. To meet essential amino acid requirements, about 11% of the RDA for total protein for adults should come from essential amino acids. This is easily achieved by most Americans.

What would be one health benefit of reducing high-protein intake(s) to RDA amounts for some people?

High-protein foods (e.g., meats and dairy products) are also typically high in fat. Therefore, reducing excess protein intake in the diet usually results in lowered saturated fat intake. This would be considered a benefit, since intake of saturated fat intake has been linked to cardiovascular disease. In addition, the nitrogen byproducts of protein metabolism must be excreted via the kidneys. In people with kidney disease, reducing protein intake may help to preserve kidney function. Excessive protein intake, which increases protein excretion, may also deplete the body of water and calcium. Reducing protein intake could improve hydration status and help to preserve bone minerals.

What is the role of cholecystokinin (CCK) in protein digestion?

In the small intestine, the partially digested proteins (and fats) trigger the release of the hormone cholecystokinin (CCK) from the walls of the small intestine. CCK causes the pancreas to release protein-splitting enzymes, such as trypsin.

Describe four functions of proteins. Provide an example of how the structure of a protein relates to its function.

Proteins have many functions such as: producing vital body constituents, maintaining fluid balance, contributing to acid-base balance, and forming hormones and enzymes. An example of how structure relates to function can be seen in hemoglobin. Its coiled shape allows it to hold iron and bind oxygen. When an error in the DNA code leads to a defect in the structure of hemoglobin (as in sickle cell disease), the shape of red blood cells is distorted and the ability of red blood cells to carry oxygen is limited.

Briefly describe the organization of proteins. How can this organization be altered or damaged? What might be a result of damaged protein organization?

Proteins synthesis is directed by the genetic code, which provides the blueprint for the order of amino acids in a protein chain. However, the sequence of amino acids in a protein only tells part of the story in terms of protein structure and function. Chemical interactions between amino acids in the protein chain cause folding of the protein chain into a specific three-dimensional structure. In addition, multiple protein chains may associate with one another to create a functioning protein. Treatment with acid or alkaline substances, heat, or agitation can denature a protein, damaging its three-dimensional shape so that it cannot function as needed.

What is a limiting amino acid? Explain why this concept is a concern in a vegetarian diet. How can a vegetarian compensate for limiting amino acids in specific foods?

The essential amino acid in smallest supply in a food or diet in relation to body needs is the limiting amino acid because it limits the amount of protein that the body can synthesize. For a person who follows an omnivorous diet, which includes the complete proteins provided by animal foods, the concept of limiting amino acids is of little concern. However, those following a vegetarian diet are not likely to consume such high-quality protein. For example, grains and nuts are low in the essential amino acids lysine, whereas vegetables and legumes and low in methionine. If only one of these plant sources of protein is consumed, the amino acid pool in the body will be limited and protein synthesis will cease. Vegetarians can compensate for this by eating complementary proteins, which in combination will provide high-quality protein for the diet. When different sources of plant protein are combined, they complement each other. For example, in a meal with beans and rice, the beans make up for the low lysine content of the rice and the rice makes up for the low methionine content of the bean

How are DNA and protein synthesis related?

because DNA contains the coded instructions for protein synthesis. The nucleic acid sequence in a segment of DNA dictates which amino acids are included in the protein.