Proteins in Foods

Questions and Answers

What percentage of an egg's weight is protein?

12%

What is the approximate protein content of a 3-ounce serving of steamed broccoli?

1 g

What is the serving size of pepperoni pizza in Table 7.3?

2 slices (246 g)

How much protein is in a 1-cup serving of vanilla ice cream?

4 g Signup and view all the answers

What is the protein content of a small banana?

1 g Signup and view all the answers

How much protein is in 2 tablespoons of peanut butter?

8 g Signup and view all the answers

What is the approximate protein content of a 4-ounce serving of roasted chicken breast?

32 g Signup and view all the answers

What is the general protein content of most plant foods per ounce?

Less than 3 g Signup and view all the answers

What is the primary source of gelatin?

Collagen, a protein derived from the connective tissue of animals Signup and view all the answers

Why does eating gelatin not make fingernails stronger?

Fingernails are composed of keratin, a protein that is different from collagen. Signup and view all the answers

What parts of plants contain more protein than others?

Seeds, tree nuts, and legumes Signup and view all the answers

How much protein does a 3-ounce serving of almonds, dry-roasted peanuts, or sunflower seed kernels supply?

About 20g of protein Signup and view all the answers

What is characteristic of mature peas, lentils, and most kinds of beans?

They contain more protein and complex carbohydrate than fat Signup and view all the answers

What is the key characteristic of high-quality proteins?

They contain all essential amino acids in amounts that support protein deposition in muscles and other tissues Signup and view all the answers

Why are egg proteins considered high-quality?

They are easy to digest and have a pattern of essential amino acids that closely resembles that needed by humans Signup and view all the answers

What are the exceptions to the rule that most plant foods are not sources of high-quality proteins?

Quinoa and soy protein Signup and view all the answers

What is the significance of understanding protein quality?

It is important for ensuring proper growth and development, as a diet lacking essential amino acids will lead to growth failure Signup and view all the answers

What is the potential health benefit of eating foods made from soybeans?

Reducing the risk of chronic diseases, such as certain cancers Signup and view all the answers

Study Notes

Proteins in Foods

Nearly all foods contain protein, but no naturally occurring food is 100% protein.
Protein comprises about 20 to 30% of the weight of a piece of beef, 25% of the weight of drained tuna fish, and 12% of an egg's weight.
Animal foods generally provide higher amounts of protein than similar quantities of plant foods.

High-Quality vs. Low-Quality Proteins

A high-quality protein contains all essential amino acids in amounts that support protein deposition in muscles and other tissues, as well as a young child's growth.
High-quality proteins are well digested and absorbed by the body.
Meat, fish, poultry, eggs, and milk and other dairy products contain high-quality proteins.
Egg protein generally rates very high for protein quality because it is easy to digest and has a pattern of essential amino acids that closely resembles that needed by humans.
A low-quality protein lacks one or more of the essential amino acids or contains inadequate amounts of these nutrients.

Limiting Amino Acids

The essential amino acids that are in relatively low amounts are referred to as limiting amino acids because they reduce the protein's ability to support growth, repair, and maintenance of tissues.
In most instances, lysine, tryptophan, threonine, and the sulfur-containing amino acids methionine and cysteine are the limiting amino acids in foods.

Plant Foods as Protein Sources

Certain parts of plants contain more protein than other parts.
Seeds, tree nuts, and legumes supply more protein per serving than servings of fruit or the edible leaves, roots, flowers, and stems of vegetables.
A 3-ounce serving of almonds, dry-roasted peanuts, or sunflower seed kernels supplies about 20 g of protein.
Mature peas, lentils, and most kinds of beans contain more protein and complex carbohydrate than fat.

Quinoa and Soy Protein

Quinoa is an exception to the rule that most plant foods are not sources of high-quality proteins.
The quality and amount of protein in quinoa seeds are superior to those of many cereal grains.
Soy protein is comparable to that of most animal proteins.
Processed soybeans are used to make a variety of nutritious foods, including soy milk, infant formula, and meat substitutes.

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Description

Understand the difference between high-quality and low-quality proteins, identify rich food sources, and learn about limiting amino acids in plant foods.