Proteins (there are many types) serve as basic building blocks of body tissues and fluids.
The best sources of protein are meats and dairy products, eggs, grains, and certain vegetables, notably beans and other legumes.
Long-term shortage of protein in the diet is extremely rare, except in countries where people don't have enough to eat or among severe alcoholics who don't get enough of their calories from food. Symptoms include poor growth, reddening of dark hair, liver damage, immune-system impairment, and general weakness accompanied by either emaciation or swelling of body tissues.
An excess of protein can lead to dehydration (see Water), because increased urination is required to break down and excrete the surplus. There is also evidence (though not conclusive) that consuming twice or more of the Food and Nutrition Board's (FNB's) Recommended Dietary Allowance (RDA) of protein will interfere with the body's ability to absorb calcium, and may lead to osteoporosis. (For a discussion of both, see Calcium.)
Your Daily Allowance
The Recommended Dietary Allowance (RDA) of protein is calculated on the average person's ideal weight¾because protein is needed mainly for lean body tissue, not fat. In its September 2002 report on macronutrients, the Food and Nutrition Board (FNB) slightly adjusted the RDA. For males, it's 52 grams from age 14 to 18 and 56 grams thereafter. For females, it's 46 grams for everyone over 14. During pregnancy, it's 25 additional grams, yielding a total of 71 grams. During lactation, it's 21.2 additional grams, yielding a total of 67.2 grams.
For years, most nutritionists recommended getting between 10 and 15 percent of daily calories from protein. In its September 2002 report on macronutrients, however, the FNB set the Acceptable Macronutrient Distribution Range for protein at 10 to 35 percent. If your weight is near the average for your age and sex and you're not on an extreme diet, the figures in the paragraph above will put you in that range. But if you're on a high-calorie diet, your PDA may push this Key Ratio under 10 percent.
As a way out of this dilemma, DietPower sets your Personal Daily Allowance of protein at the number of grams required to make up a generous 15 percent of your calories. For most people most of the time, this will also satisfy the RDAs (see above). To make certain you're meeting the RDAs, however, you should occasionally look at the number of grams of protein you're averaging in your Nutrient History. This is especially important if you're pregnant, nursing, or greatly over- or underweight.
The FNB has not established a Tolerable Upper Intake Level (UL) for protein, but see the note about dehydration, above.
Revising Your Allowance
If your doctor advises a higher or lower protein intake, you can change your PDA. See Personal Daily Allowances, Editing Your.
Color Coding of This Nutrient
The protein bar in your personal Nutrient History is:
blue for "good" if you've logged 100 to 150
percent of your PDA
red for "bad" if you've logged less than 100
percent of your PDA
yellow for "caution" if you've logged more
than 150 percent of your PDA
missing if you've logged no protein
In the nutrient profile of a food or recipe, the protein bar is:
green for "good" if getting your entire PDA
of calories from this item would give you more than 150 percent of your
PDA of protein
magenta for "bad" if getting all your calories
from the item would give you less than 50 percent of your PDA of protein
blue for "neutral" otherwise
missing if the amount of protein is either zero or unknown
How Complete Are DietPower's Protein Readings?
Absolutely complete. Of the 11,000 items in the Food Dictionary, none list their protein content as "unknown."
(There will be unknowns, of course, if you've added foods to the dictionary with missing protein figures. But these won't be marked as unknowns. Since protein is one of the four energy nutrients, DietPower needs a figure in the Protein column in order to calculate a food's calorie content. If you leave a blank or a question mark there, the program automatically changes it to a zero.)
To see whether a particular food has a protein reading, open the Food Dictionary and check the food's nutrient profile. If you find a question mark beside "Protein," it means the amount is unknown. (To see all foods with unknown protein readings, click the dictionary's PowerFoods tab and sort the foods by protein power; then scroll toward the bottom of the list until you see foods with question marks in the "Power Rating" column.)
Protein on Food Labels
Virtually all food labels are required to report protein content, both in grams and as a percentage of Daily Value.
The Daily Value for protein is 50 grams for a person eating 2000 calories per day. (At four calories per gram, this means exactly 10 percent of the person's calories would come from protein.) This amount is not necessarily right for you, however¾it's a rough estimate meant to accommodate most of the U.S. population.
For more on label regulations, see Labels, Food.
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Last Modified: 7/27/07