A Table of Food Values

BERNICE KUNERTH WATT, ANNABEL L. MERRILL, AND MARTHA LOUISE ORR.

THE table we present here provides typical values for the nutrients in foods that are of particular importance in evaluating diets and planning meals.

The nutrients listed are protein, fat, carbohydrate, two minerals (calcium and iron), and five vitamins (vitamin A, thiamine, riboflavin, niacin, and ascorbic acid). Percentages of water in food and also the Calories, which denote the amount of fuel or food energy released to the body by the oxidation of protein, fat, and carbohydrates, are shown.

The table is based on analytical data in scientific and technical journals published all over the world and on all other data available to us from published and unpublished sources.

Future tables of food composition for general use will include additional nutrients and many new kinds and forms of foods.

The growing volume of laboratory findings already has made it possible in the case of one nutrient, protein, to publish separate values for 18 of the component amino acids. Data on specific components of fat and carbohydrate are becoming available.

All the substances we need for good nutrition are in the plants and animals of the world around us. We use leaves, stems, berries, seeds, roots, and tubers of plants; the muscle, liver, blood, and other parts of animals; and many forms of the life of the sea.

Differences in kind and amount of main nutrients are apparent in many foods. Milk, for example, is outstanding for its calcium but has little iron. Meat provides excellent protein but has only negligible amounts of calcium. Oranges are superior sources of ascorbic acid (vitamin C) but have almost no protein.

Similarities in nutrient content exist among many foods. Meat, fish, and poultry, for example, are excellent sources of protein. If to these we add such good sources as eggs, milk, dry beans and peas, and nuts, we have what we call the protein group.

Green and yellow vegetables are good sources of carotenes, precursors of vitamin A. Vitamin A value is a term that may refer to vitamin A itself or to one of the carotenes, which the body can convert to vitamin A.

Citrus fruits, tomatoes, fresh strawberries, and cabbage are among the many foods valuable for their content of ascorbic acid--a vitamin that often is referred to as vitamin C.

Whole-grain cereals, those with added vitamins and minerals, and those restored to the level of whole grains provide sizable amounts of iron, thiamine, riboflavin, and niacin.

These are only a few examples of natural groupings of foods on the basis of similarity of nutrient composition. Such groupings lend themselves to a great variety of uses in appraisals and calculations of diets.

Variations in amount of nutrients also occur in different samples of the same kind of food. The protein content of one sample of wheat may be nearly double that of another. The fat content of milk depends upon many factors, including the breed of the animal. The content of carotene, or vitamin A value, of carrots extends over a wide range.

In the preparation of our table of composition of food, we make such differentiations as seem indicated in order to get representative values.

We subdivide some groups of food according to characteristics that we know are associated with nutrients as variety, degree of maturity, Storage conditions, the way a food is prepared for market, and the kind and degree of processing.

We must take into account the distinguishing characteristics of each food when we set out to derive average or representative nutritive values. Two familiar foods, oranges and potatoes, illustrate the complexity of obtaining values suitable for various purposes.

Oranges are particularly important for their content of vitamin C, but single oranges may show great variation. From the hundreds of analyses of the vitamin C in orange juice, we have learned that 100 grams (a scant half cup) of the juice may have less than 20 to more than 80 milligrams of vitamin C.

The variety of the orange accounts for much of the difference. Navel oranges from California have an average of about 60 milligrams in 100 grams of juice. California Valencias and Florida-grown early and midseason varieties (Hamlin, Parson Brown, and Pineapple) average 51 milligrams. Florida late-season Valencias average 37 milligrams of vitamin C.

The vitamin C in orange juice varies also with the time the oranges are picked. It is higher early in the harvesting season than toward the end of the season. We used data on the quantities picked at different times throughout the harvest period to derive an average value of vitamin C for each variety of orange. Then, so as to get the average value for a year on a national basis, we studied data for individual varieties. We took into account the relative proportion of each variety in the total production of oranges shipped for the fresh-fruit market. This year-round, countrywide value for fresh oranges is 50 milligrams of vitamin C per 100 grams of juice. (There are nearly 250 grams in a cupful of juice.)

The average amount of vitamin C in orange juice from the important commercial varieties varies throughout the year. Values are high in November February, when a cupful of juice provides about 132 milligrams of vitamin C. They are low in August September, when the average drops to about 110 milligrams. During the other 6 months, the juice has an intermediate value of about 119 milligrams per cupful. The average values on an annual basis for juice from all the important commercial varieties is 124 milligrams per cup.

Frozen orange juice concentrate is prepared mainly from Florida oranges. The average content of ascorbic acid of juice of the commercially important varieties from Florida, including the Temple oranges, is about 45 milligrams per 100 grams of juice-112 milligrams per cupful.

The loss of ascorbic acid during processing is negligible; the value for frozen reconstituted juice is the same as for Florida fresh juice. The value of the reconstituted frozen juice is a little lower than the national, year-round value for fresh orange juice because California-grown oranges comprise a large proportion of the total shipped for use as fresh oranges but only a small proportion of the total oranges used for the frozen concentrate.

Grapefruit, unlike oranges, shows little varietal difference in amount of ascorbic acid but does have a similar seasonal trend of decreasing content as the harvest season progresses. The average values of the four types on the market white seeded, white seedless, pink seedless, and pink seeded fall within the range of 36 to 39 milligrams per 100 grams of pulp or juice.

The Florida-grown grapefruit, which makes up the greater share of the total market supply, has the highest content of ascorbic acid in the fall when the harvesting season begins and the lowest content in the late spring at the end of the season.

The high values of September and October average about 42 milligrams per 100 grams for white-fleshed varieties and 44 to 47 milligrams for pink-fleshed grapefruit. The lowest values in May average 33 to 35 milligrams for all varieties.

California and Arizona grapefruit show a similar trend, starting with a value of about 44 milligrams in September and dropping to 36 milligrams in August.

We must keep a different set of characteristics in mind when we derive average values of potatoes.

POTATOES furnish several nutrients. One is ascorbic acid, which may vary widely. Some potatoes have more than 50 milligrams per 100 grams of Potato; others, less than 5 milligrams.

Length of the storage period has an important influence on the content of ascorbic acid. Maturity and variety also affect nutritive value.

The highest content of ascorbic acid is in immature potatoes, which sometimes are grabbled for home use before the crop is ready to dig. Their ascorbic acid value averages about 35 milligrams per 100 grams. Since few, if any, of these young potatoes get into commercial channels, however, data for these are not included in our average values for potatoes.

"New" potatoes that is, potatoes recently dug and not stored are on the market nearly all year. Some plantings are primarily for the production of new potatoes. Usually they are dug before they are fully mature, and do not keep well. Other plantings are for harvest when the crop is mature. Some of these are sold as new potatoes, and the others are put in storage.

The average content of vitamin C for the different varieties of major commercial importance is in the range of 19 to 33 milligrams per 100 grams.

A good general figure for all new potatoes on the regular market is 26 milligrams per 100 grams.

Most of the potatoes sold in winter and spring have been taken out of storage. The vitamin C in stored tubers drops progressively from December to the end of July. About one-fourth of the ascorbic acid is lost by the end of the first month; about one-half after 3 months; and two-thirds after 6 months. Any on hand after 9 months of storage have lost three-fourths or more.

The ascorbic acid value of the total market supply for January, February, March, and April (weighted by the proportion of new and stored potatoes) is 13 to 14 milligrams per 100 grams of potato. The value rises to 18 milligrams in May with the increased volume of new potatoes and goes on up to 25 milligrams in summer and fall. It drops back to about 18 milligrams in December.

The average year-round value for ascorbic acid in potatoes of commerce, taking into account variety and storage, is 20 milligrams per 100 grams.

THE DERIVAT10N of representative composition values brings to light many interesting similarities and differences among foods in the various food groups.

Like members of a family, foods in a group have some features that are similar and some that are individualistic. We note some of these features in the major groups of foods.

MILK as produced by the cow has a lower percentage of water than many succulent fruits and vegetables.

The average composition of milk is about 87 percent water, 3.5 percent protein, 4 percent fat, 5 percent carbohydrate, and a little less than 1 percent ash (minerals). These milk solids are an outstanding source of calcium and a good source of riboflavin, high-quality protein, vitamin A, thiamine, vitamin B₁₂, and other dietary essentials.