The Nutritive Value of Animal Foods, Fruit, and Vegetables

New Zealand Journal of Agriculture, Volume 79, Issue 2, 15 August 1949, Page 185

The Nutritive Value of Animal Foods, Fruit, and Vegetables

r T"’HE nutritive value of cereals and milk and its products, two of ■ , . . r r if* . <« ’ « • the most important classes of food, both economically and nutritionally, was discussed in an article in last month’s “Journal” by 1 7 i- km i i 7 Evelyn E. Moore, Rural Sociologist, Department of Agriculture, Auckland. The value of other nutritionally-important —animal foods (such as meat and eggs), vegetables, and fruit— the subject of this article. The third and final article in the series, to appear next month, will deal with fats, beverages, and some of the foods which, because of low nutritive value or high cost in proportion to their nutritive value, should not be allowed to figure too prominently in the menu.

AS long as New Zealanders maintain their place at the head of the list of meat-eating peoples it is most unlikely that the average person will ever fail to obtain sufficient highquality protein from his diet. However, though the amount of meat eaten probably could be reduced considerably without any ill effect on health, it is certainly not recommended that people go to the other extreme and become vegetarians. Eggs, Meat, and Fish Three foodstuffs which have much in common are eggs, meat, and fish. With milk and cheese they provide the high-quality protein essential for growing children, and for adults, too. The, protein in these foods is, perhaps, of the greatest value nutritionally, for one serving of eggs, meat, or fish, with the amount of milk recommended for

health (1 pint for an adult and If pints for a child), provides all the high-quality protein essential for growth and health. These foods are also excellent sources of the mineral phosphorus (an essential nutrient required for both bone and tissue growth and maintenance), which is rarely deficient in the New Zealander’s diet, simply because sufficient and often more than sufficient meat is eaten. Third, they are fair sources of energy. Moderately-fat mutton and beef have about the same calorie content as bread; very lean meat, kidneys, brains, and fish have about half the energy value of bread, and liver and eggs occupy an intermediate position. Fourth, they are all good sources of at least one vitamin. Though the vitamin content of meat from organs

and muscles, as well as from different animals (beef and pork, for example), varies somewhat, the variation is seldom so great as to cause one class of meat to be regarded as definitely in-

to ot £ er cla sses in food value. Muscle meat is a good source of niacin and riboflavinvitamins belonging group and affair source of other B vitamins. Fish also contains them, but usually in smaller amounts. Poultry, rabbit, tongue, and most sources VSe serving will provide from a fifth to the whole the^July requirement quirement of riboflavin. Fifth, they are all at least fair sources of iron.

Like all other foods, however, eggs, meat, and fish are not ideally balanced nutritionally, being deficient in several nutrients, perhaps the most important of which is calcium. Eggs contain more calcium than does meat, but cannot be rated as good sources, for one egg provides only about 3 per cent, of the daily need for calcium. Consequently they cannot be substituted for milk or cheese, though in other respects their nutrient content may equal that of these foods. Second, like cereals and milk, these foods contain negligible amounts of vitamin C. Third, they are, with the important exceptions of liver, kidneys and eggs, very poor sources of vitamin A. The cost of these foods also limits their use, particularly in low-cost diets, for though they are little more

expensive sources of good-quality protein, energy, and some vitamins than milk or cheese, they contain no calcium. Consequently, as milk must be included in the diet to provide calcium, it is also relied on to provide most of the high-quality protein and vitamin B 3 and whole cereals and the cheaper root vegetables are used instead of meat as sources of iron, calories, and other nutrients in the low-cost diet. Unique Value of Liver The nutrient content of some foods in this group; is better than that of others, and that is particularly true of liver, pork, and eggs. Liver occupies a unique place among foods because of its high nutrient content. Yet, though its chief disadvantage as a food is its limited availability, it is likely that much sound liver, particularly on farms where meat is home killed, is not used because of the prejudice which has developed against its use and the fear that it may cause hydatids; this belief has no foundation in fact, for it is impossible to develop hydatids directly from cooked food or, indeed, any —provided it has not been contaminated with, hydatid eggs from dust or dogs. Liver is the best food source of iron and vitamin A, one serving providing more than the whole daily .requirement of either of these nutrients, and. it is one of the best food sources of all the vitamins in the . B group and of protein. Thus it is well worth a place in the menu when it is available, as. its use is an insurance against anaemia. Therefore, it is an especiallygood food for infants, adolescent girls, and expectant mothers, whose need of iron is greater than that of other members of the community. Eggs also have a higher, nutritive value than ordinary muscle meat, for they are a good source of vitamin A (one egg contains about a sixth of the daily requirement) and of iron in a very easily assimilable form. Pork and bacon are particularly valuable for their vitamin :B, content as they contain about 10 times as much as beef, two or three times 'as much as wholemeal bread, or a quarter the amount present in vegetable extracts. Therefore they are practically the richest ordinary food sources of this vitamin. Though their inclusion in the menu is not essential for a healthful diet, they are, from the ■ nutritive point of view, more worthy of the money spent on them than, for example, an expensive piece of undercut steak. A serving of pork also provides at least five times as much vitamin B, as a teaspoonful of vegetable extract, and other nutrients are present in pork as well. Therefore, though eggs, w meat, and fish have a valuable place in the diet, they require to-be bal- . anced with milk and cheese to provide calcium: and vitamin A, vegetables and fruit to provide vitamins C and A, and cereals to provide energy at a lower cost than is possible with meat and eggs. Vegetables The need for eating plenty of vegetables to maintain health and fitness is well known, but. perhaps not until the war years, when they were often

the sole sources of vitamin C and almost the only foods supplying vitamin A in the diets of Britons and other Europeans, was their value fully appreciated. In addition, some of them provide fair amounts of good-quality protein . and iron, and when milk was not obtainable they became one of the biggest suppliers of calcium. In fact, they formed a large part of the diet of many people in the occupied countries and were responsible for the general health of northern Europeans being as good as it was, as well as for the absence of such diseases as scurvy and : blindness caused by vitamin A deficiency. Their chief defect was their low energy value, so that it was almost impossible to eat sufficient to provide for the energy requirements of the body. When plenty of energy foods are available that aspect is unimportant, for the worth of vegetables, like that of milk, is far from being assessed by their energy value alone. However, they do vary considerably in nutritive value, so much so that it is recommended that not only vegetables, but vegetables from each of the two main groupspotatoes and other root vegetables and green vegetables be eaten daily. ; ' Any classification of vegetables into groups must be decidedly arbitrary, but the following may suffice: — Green and leafy vegetables, including ' the cabbage family, .he spinach family, leguminous green vegetables, and many salad vegetables. Roots ana tubers. Fruits and seeds, including cucumbers, chokos, egg fruit, marrows, mushrooms, pumpkins, and tomatoes. Green and Leafy Vegetables Vegetables in this group are valued mainly for their content of vitamins A and C. Even within the group, however, they vary greatly in their vitamin content. Therefore while it is recommended that at least one generous serving of vegetables from this group be included in the menu daily, it is also recommended that the choice be made from as wide a selection of vegetables within the group as possible, so that any individual nutritional defect of a food in this class will not be unduly accentuated. To take an extreme example, these vegetables are nearly all good sources, of vitamin A, but cauliflower contains none at all, though it is an excellent source of vitamin C and a fair source of other vitamins and minerals; thus, it is possible that, if cauliflower were the only vegetable in this group to be eaten, a slight vitamin A deficiency might develop. These vegetables should always be used as fresh as possible, for vitamin C is lost quite rapidly during storage, and, if they are allowed to wilt, green vegetables often contain negligible amounts of the vitamin. The : Cabbage Family . This group includes cress, cauliflower, brussels sprouts, turnip tops, and kale. As their energy, value (5 calories per ounce) is only about a

fourteenth that of bread, obviously their nutritional value is the result of their vitamin and mineral content. Some of them, particularly kale and turnip tops, are good sources of calcium and iron, 3oz. of either containing about a tenth of the daily requirements of these minerals, and many contain large amounts of carotene or pro-vitamin A, which is usually present only in the green leaves, the amount depending on their greenness. A serving of turnip tops will provide a quarter or more of the daily requirement of vitamin A, but the white heart leaves of a winter cabbage none at all. However, their chief value nutritionally is in the provision of vitamin C, as a serving of any one of them, freshly picked and cooked rapidly in a minimum of boiling water or in a pressure saucepan, will contain at least half the daily vitamin C requirement. Used raw in salads they provide even more of this vitamin, but, as it is usually impossible to eat as much raw cabbage, for example, as cooked cabbage, the total vitamin C obtained from a raw green vegetable salad is probably about the same as that from a generous serving of the cooked vegetable, provided it has not been overcooked, cooked with baking soda, or left standing a long time, before being served. The Spinach Family Ordinary and New Zealand spinach and silver beet are as good sources of vitamins A and C as the cabbage family, but they contain small amounts of oxalic acid salts which make their own calcium and iron, and probably some of the calcium in other foods, useless to the body. However, to presume that' for this reason they are harmful foods and should not be eaten is quite incorrect, for the oxalates are not nearly concentrated enough to affect health. Yet, if they figure frequently on the menu, it is important to ensure that rather, more than the recommended allowance of milk is included in the diet, so that sufficient calcium is consumed to compensate for the wastage which occurs when some of the oxalic acid combines with the calcium in milk ,or other foods and thus prevents it from being absorbed from the intestine. When this precaution is observed these vegetables are valuable,", especially as they can be grown to be ready at times when other vegetables are scarce. Peas and Beans Though french or runner beans are not very nutritious vegetables, containing less than half as much vitamins A and C as green vegetables and small amounts of other nutrients, peas : and other beans are much more nutritious and have perhaps the highest all-round nutrient content of any vegetable. They contain about half as much vitamin C as cabbage, and peas contain about half as much vitamin A. Their vitamin B, content is equal to that of wholemeal bread, and they are good sources of other of the B vitamins and iron and fair sources of protein and calories or energy. Their general

popularity as vegetables is certainly justified if food value is to be the criterion.

Salad Vegetables

Lettuce, celery, radish, spring onions, chives, parsley, cucumber, tomatoes, endive, cress, and watercress are probably the most important vegetables in this section, for they are most often eaten raw. It is usually recommended that raw vegetable salads be eaten frequently to provide vitamin C, because if vegetables are cooked too much, too slowly, with soda, or in a large quantity of water, or are kept hot in dishes for a long time before being served, most of the vitamin C will be destroyed, and sometimes it is difficult to avoid some of these practices.

However, salads of the type frequently served in New Zealand restaurants or two lettuce leaves and a slice of tomato— salads which consist mainly of chopped lettuce with a ' sprinkling of egg, tomato, or other vegetable on top, cannot be relied on to make good any deficiency in vitamin C, for lettuce is not a very good source of this vitamin. For example, 3oz. of lettuce very generous serv—provides only about a third as much vitamin C as a similar quantity of cabbage or silver beet cooked quickly in a minimum of water.. Celery and cucumber are even poorer sources of vitamin C, but other salad vegetables, especially tomatoes and cress, contain important amounts of vitamins C and A. Some of these vegetables, especially parsley, chives, and mint, can be used only in small amounts because they are strongly flavoured, so that, though they do not detract from the nutritive value of the salad, they do not greatly improve it.

Cabbage salads, or salads in which tree tomatoes, tomatoes, and cress, for example, are not used merely for flavouring but are important ingredients, have a higher nutritive value and provide between a third and two-thirds of the daily requirement of vitamin C. Cooked vegetables such as peas, carrots, and potatoes, while contributing to the general nutritional value of the salad, are also unreliable sources of vitamin C, much of it often being lost while the vegetable is kept after being cooked.

Therefore, salads, if they are served with the intention that they should be the main source of vitamin C in the menu for the day, should contain plenty of some of the good sources of this vitamin— is, they should either be cabbage salads or contain generous amounts of tomatoes, tree tomatoes, or other vitamin-rich fruit, or watercress. Other salad vegetables make a useful contribution to the daily needs of vitamins and minerals, but they are not as valuable nutritionally as is often supposed.

Roots, Tubers, and Pumpkins

Many of these vegetables have a higher energy value than green vegetables, but usually they contain less vitamin C. and vitamin A. Kumar as, yams, potatoes, and parsnips contain the most starch and therefore have the highest energy valueabout a third that of bread. Some of the others,

especially white turnips and swedes, have no higher energy value than green vegetables. Those with the Highest energy value are fair sources of vitamin B 1( soz. of potatoes—a generous serving—containing at least a tenth of the daily requirement. They are all fair sources of vitamin C, particularly swedes, and yellow vegetables, kumaras, pumpkins, and especially carrots are good sources of vitamin A.

In addition, root vegetables, unlike green vegetables, retain some vitamin C even after, long periods of storage; freshly-dug potatoes provide half of the daily vitamin C requirement per serving, and after 6 months’ storage provide at - least a tenth of the requirement. Consequently,: as they also are fair sources of other vitamins, energy, and iron, they are of rela-tively-high nutritive value and should not be omitted from the menu even by overweight people; for there are many less nutritious foods with a higher energy value which could with benefit be excluded instead.

Other Vegetables

Marrows, sweet corn, chokos, egg fruit, and mushrooms have less food value and especially less vitamins C and A than other vegetables, though when cooked and eaten with butter, as they often are, their vitamin A and energy value are increased considerably.

Fruit The nutritional value of fruit depends largely on its vitamin C or ascorbic acid content, for, excluding vegetables, they are the only foods which contain more than negligible amounts of this essential. vitamin. Apart from their energy value, which, though not. high, is generally greater than, that \of vegetables , (bananas, grapes, figs, and black currants all have an energy value similar to or greater than that of potatoes), they are usually poorer sources of other nutrients, so their nutritional value may be estimated mostly in terms of their vitamin C content.

Fruits .which contain much vitamin C, such as black currants, rose-hip syrup, citrus fruits, other berry fruits, passion fruit, tomatoes, tree tomatoes, pineapples, , persimmons, gooseberries, Chinese gooseberries, rock melons, and Sturmer apples are the most nutritious. Other apples, quinces, apricots, nectarines, peaches, bananas, and rhubarb contain moderate amounts of vitamin C (an average apple or banana provides about a sixth of the daily requirement) and, like other fruits, add relatively-small amounts of other minerals ? and vitamins to the total daily consumption.

Most of the other fruits which are poor sources of vitamin C, including grapes, figs, loquats, pears, plums, and cherries, , are also popular and even have a reputation for being nutritious, but as 4oz. of any contain a fifteenth or less of, the daily vitamin C requirement, and as their content of other nutrients is uniformly low, they must take their place with chocolates, jellies, and other foods as very pleasant. desserts without which the

menu may be less interesting but which are not necessarily included in the healthful diet.

Tinned Fruits and Vegetables

There are still some people who are prejudiced against the use of tinned fruits and vegetables, though the quality of the food used for preserving, as well as the standards of hygiene and treatment, have improved so much that the nutritive value of tinned vegetables is equal to and sometimes greater than that of homecooked vegetables, especially if the latter have been picked and stored for some time before use. Consequently, they can be substituted for homecooked vegetables whenever necessary with complete confidence, though naturally the vitamin C content is somewhat less than that of the raw vegetable. Tinned fruits also retain their vitamin C well.

Home - bottled vegetables, because they have to be cooked for long periods to ensure that they will keep, are not reliable sources of vitamin C.

Dried Vegetables

Beans, peas, and lentils are the principal dried vegetables in use, for, though methods of drying and storing other vegetables have improved greatly in recent years, the fresh ones are still infinitely to be preferred, particularly in New Zealand, where some fresh vegetables are available throughout the year.

Dried peas and beans, haricot beans, or split peas all have a airlyhigh nutritive value. Vitamin C is destroyed and they contain negligible amounts of vitamin A, but they are . good sources of vitamins of the B group and iron and fair sources of protein and energy.

Value of Balanced Diet

This article and the previous one have been concerned with the nutritive value of the majority of the foods which are necessary for the healthful, well-balanced diet. Their great variation in nutritive value may seem surprising at first and may even cause wonder that malnutrition does not occur more frequently. Fortunately, the average diet consists of a reasonably well-balanced mixture of these foods, so that nutrients lacking in one are provided in abundance by another. In addition, the body has a very good ability to store most nutrients, so that a surplus of, say, vitamin A obtained one day, when the menu includes liver for breakfast, carrots for dinner, and a green salad for lunch or tea will be utilised a week later when cauliflower and potatoes are served with the meat for dinner and when, apart from milk and butter,, other good sources of vitamin A are not included in the menu.

As long as food fads and preferences are not allowed to play too important a part in the composition of the diet, which should consist predominantly of foods from each of the four main groups—whole cereals; milk, dairy products, and meat; vegetables and fruits; and fats—malnutrition is unlikely to occur.