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Carbohydrates

Generally carbohydrates are not considered in nutritional recommendations since only 50 g daily is sufficient to avoid ketosis. However, carbohydrates contribute more than half of the energy in the diets of almost all the world's populations. Given the recommendations for proteins and fats, carbohydrates should provide between 60% and 70% of the total energy of the diet.

Conditions such as obesity, diabetes, and some cardiovascular diseases are related to excessive energy consumption, which in Latin American diets frequently comes from an excess of carbohydrates.

The ingestion of certain carbohydrates such as sucrose and lactose merits special consideration.

Sucrose

Sucrose is the sugar most common in diets. It is hydrolysed by enzyme action in the intestinal tract to glucose and fructose, which are easily absorbed. Sucrose represents a concentrated source of energy that is agreeable in taste and relatively inexpensive in Latin America. Because of this it can contribute to increasing the diet's energy density. However, it must be taken into account that it supplies "empty calories" in the sense that it contains no other nutrients.

Some advocate limiting the use of sucrose because of its association with a greater incidence of dental caries, due to the proliferation of bacteria in the mouth that use sucrose as a substrate. This effect can be reduced by reducing the consumption of sucrose during and in between meals, and by using good toothbrushing techniques. Other preventive measures such as fluoridation of water or the topical application of fluoride also contribute to reducing the incidence of caries.

It is advisable to limit its use except when it is required for the diet to reach necessary energy density.

Lactose

Lactose is the sugar in milk. It is hydrolysed in the intestinal tract by the enzyme action of lactase, giving rise to glucose and galactose. It is the principal carbohydrate in the diet of the nursing child. Milk provides, furthermore, proteins of high biological value, calcium, and other nutrients.

In Latin America, as in other regions, the majority of people have a gradual reduction of lactase from preschool age. In consequence, the consumption of lactose in quantities that exceed the capacity of the small intestine to hydrolyse it results in its reaching the colon undigested. Then fermentation by the bacterial flora produces gas and sometimes causes symptoms of flatulence, diarrhoea, and/or pain. However, there are relatively few people who do not tolerate the ingestion of moderate quantities of milk or milk products. The effects of pharmacological doses of lactose that are used in some tolerance tests are not a reliable indicator of the acceptability of milk consumed in customary quantities that generally provide between 10 g and 15 g of lactose. Programmes to distribute milk to children should not be discarded, nor should the use of milk in dietary management be restricted on the basis of its lactose content. The use of commercial milks with a reduced quantity of lactose, although convenient for the treatment of some clinical symptoms, is not justified for the general population and its cost is high.

Digestible complex carbohydrates

These are principally starches and dextrines, which constitute the main source of energy in the majority of Latin American diets. In contrast to sucrose, complex carbohydrates are not ingested in pure form but as part of a food. Cereals, roots and tubers, and some fruits provide the majority of food starches and are also important sources of other nutrients. Because of this it is preferable to eat complex carbohydrates instead of refined sugars. However, the majority of foods rich in starches become voluminous upon cooking. This limits the quantity that one can ingest, particularly for children, and must be taken into account.

Fibre

Food fibre-derived from the cell walls and intercellular structures of plants-is made up of complex polysaccharides, phenylpropanes, and other organic components that are not digested in the human small intestine, and so it arrives undigested at the large intestine.

Composition

For many years food fibre was measured as "crude fibre" on the basis of its insolubility in strong acids and alkalis. This analytic method determines cellulose and lignin, corresponding approximately to what is today defined as the insoluble part of food fibre. It was assumed that crude fibre was metabolically homogeneous and inert. Today it is known that the various components of food fibre, such as cellulose, hemicelluloses, pectins, mucilages, gums, and lignin, differ in their physical-chemical characteristics and functions in regard to the intestine. The composition of fibre varies in different species of vegetables and is modified by the age of the plant. In addition, the preparation and cooking of many foods influences the quantity of food fibre that is not digestible. Therefore, the values for crude fibre in the food composition tables used in Latin America are obsolete.

An international group of experts is compiling information for LATINFOODS to update the tables of food composition to include the different components of fibre. This will also affect the estimate of metabolizable food energy, since digestible carbohydrates are usually calculated by difference after analysing the content of proteins, fats, crude fibre, moisture, and ash. Furthermore, the contribution of metabolizable energy derived from volatile fatty acids that are produced in the colon by bacterial decomposition of some fibres will have to be considered.

Functions

A certain amount of fibre is essential for normal gastrointestinal functioning and for the prevention of afflictions such as constipation and diverticulitis of the colon. An association has been noted between the ingestion of food fibre and the prevention or improvement of diseases such as diabetes, colon cancer, and arteriosclerosis, although the data are not conclusive.

The physiological effects of fibre are variable but depend on the proportions of its components and their physical characteristics. Some polysaccharides are fermented by bacteria to short-chain volatile fatty acids that produce flatulence and an acid medium in the large intestine. The components of polar groups affect the absorption of nutrients, faecal weight, and velocity of transit in the stomach and intestine. Lignin, pectin, and some acid polysaccharides affect the excretion of biliary acids and reduce the absorption of cholesterol, while other acid polysaccharides increase the excretion of minerals.

There is some evidence that the elderly metabolize greater quantities of fibre than young people. It is assumed that this is related to slower intestinal transit and alterations in the intestinal bacterial flora.

Dietary fibre can interfere with the absorption of energy and some nutrients. For this reason, it is recommended that the consumption of dietary fibre not be increased in populations with a high consumption of foods of vegetable origin. However, for populations with a high consumption of animal products and few vegetables, it is advisable to increase the intake of foods rich in fibre. In the absence of more precise information, it is believed that the diet of young adults should provide at least 20 g daily of fibre, measured by an analytical method that determines both water-soluble and insoluble dietary fibre. This would correspond to a minimum of 8 g or 10 g per 1,000 kcal.

Fats

Certain fats are essential in the diet because they provide fatty acids that cannot be synthesized in the human organism. The essential fatty acids form part of the phospholipids of cellular membranes and are precursors of substances that have regulatory functions, such as prostaglandins, protacyclines, thromboxins, and others.

Food sources

The principal sources of fats are the so-called "visible fats" of the diet, among which are butter, margarine, oils, mayonnaise, cream, and lard. Other important sources of fat are various foods of animal origin, such as meats, whole milk, and many cheeses, and also nuts and oleaginous seeds.

Fish are a source of fats of potential benefit, since their fats are rich in essential fatty acids, especially those in the n-3 series. Many marine and freshwater fish in Latin America have important concentrations of these fats.

Essential fatty acids

Dietary fats must supply adequate quantities of essential fatty acids in the series of linoleic acid (n-6) and alpha-linolenic acid (n-3), which cannot be derived from each other. Furthermore, the sources of these acids are different. The acids in the n-6 series are abundant in oil seeds, while those in the n-3 series are abundant in leaves and fish. It is estimated that an adult needs about 3% of total food energy in the form of essential fatty acids. It is not difficult to ingest this quantity with customary diets, even when they have a low total fat content.

The requirement for these fatty acids for nursing children is on the order of 5% of food energy, a quantity that is easily provided by maternal milk or cow's milk, except when it is skimmed. For this reason and because of its low energy density and poor content of other nutrients, the use of skim milk in the feeding of nursing or young children must be avoided, or at least foods rich in essential fatty acids and other missing nutrients should be added to or included in diet.

It is recommended that between 10% and 20% of the polyunsaturated fatty acids in the diet be of the n-3 series. The need for series n-3 acids can be satisfied by alpha-linolenic acid, which is found in a high proportion in soybean oil, or by its derivatives eicosapentonoic and decosahexanoic acids, which are found in fish and in the fat of wild animals.

Recommended fat intake

Fats are a concentrated source of energy, highly useful in increasing the energy density of diet. This is particularly important for young children who have limited gastric capacity. For this reason, and on the basis of fats providing essential fatty acids and their influence on the absorption of liposoluble nutrients, it is recommended that fats make up approximately 20% of the total energy of the diet, but not more than 25%. Some nutritional guidelines recommend a maximum limit of 30% of energy in the form of fats, but this is considered excessive on the basis of experimental results and recent epidemiological evidence regarding health disturbances associated with that high an intake of fats.

In addition, it is recommended that the fat intake comprise approximately equal parts of saturated, mono-unsaturated, and polyunsaturated fatty acids. In any case, the intake of saturated fatty acids in quantities exceeding 8% of total food energy should be avoided. On the other hand, the quantity of mono-unsaturated acids could be greater than 8% of the total energy, on the basis of recent investigations using olive oil.

Palm and coconut oils

The oil from coconuts is highly saturated and should be used in human nutrition only within the limits for saturated fat of 8% of total food energy.

In various Latin American countries the production of palm oil has grown as an attractive economic option. The crude oil of the African oil palm has 50% saturated fatty acids (principally palmitic acid), 40% oleic acid (mono-unsaturated), and only 10% linoleic acid (polyunsaturated). However, the product refined for human consumption, palm olein, has a smaller proportion of saturated acids. Recent studies on experimental animals and humans indicate that palm olein does not increase the level of serum cholesterol [8], although it does not reduce it significantly, as oils with a higher proportion of polyunsaturated fat, such as corn, sunflower, and sesame oils, have been observed to do in similar studies. It is necessary to note that there are still a great number of questions on this topic which should be investigated.

Cholesterol

Cholesterol is not a nutrient that needs to be supplied by the diet, but it was considered in the meeting because its ingestion in excess should be avoided. The foods richest in cholesterol are eggs (a yolk contains between 200 and 300 mg, according to its size), butter, sausage, cream and products containing it, seafood, and viscera. Among the latter, brains contain very high quantities, up to 2,000 mg per 100 g.

Even though cholesterol forms an important part of cellular membranes and is a precursor of various hormones, there is no dietary requirement for it, because the organism can synthesize all the cholesterol needed. On the other hand, it has been shown that people can vary the synthesis of endogenous cholesterol depending on the amount of food cholesterol. This capacity to adapt is not unlimited, and at intakes above approximately 300 mg per day, part of the population shows an undesirable increase in the concentration of plasma cholesterol. It is therefore considered prudent to recommend that cholesterol intake not exceed 100 mg per 1,000 kcal for adults.

As far as children are concerned, it should be recognized that in various Latin American populations eggs provide a significant part of the proteins of high biological value in the diet. Considering this, and in the absence of further evidence, it is suggested tentatively that for children cholesterol intake should not exceed 300 mg per day, equivalent to an average of 1 or 1.5 hen eggs a day.

Vitamins

This document considers only vitamins whose intake represents an existing or potential nutrition problem in Latin America. These are vitamin A, vitamin C, folic acid, and, to lesser extent, thiamin, riboflavin, and niacin. It is accepted that, if diets are modified so as to correct deficiencies of these vitamins, it is highly probable that they will be adequate in all other vitamins.

The concept of "nutrient density" was used, with vitamin requirements expressed as quantities of each vitamin per 1,000 kcal of the diet (table 4), because this focus facilitates the planning and formulation of diets for the family and population, especially in the case of micronutrients. This implies that if the diet is ingested in quantities sufficient to satisfy energy needs, vitamin needs will also be fulfilled. This approach results in intakes that may be higher than those recommended for some groups as a function of their age, sex, and physiological state. However, it is considered that they can be attained with the usual diets in Latin America. It should be recognized, however, that if the different foods of a mixed diet are not eaten in balanced proportions, the intake of some nutrients could be insufficient even though total food energy needs are met.

TABLE 4 Daily vitamin needs

Sources: Refs.2 and 3.
a. Supplementary amounts.

This concept was applied from six months of age, since there is no convincing evidence that vitamin needs in relation to dietary energy are different in the different age and sex groups, with the exception of folates for pregnant women. The vitamin requirements of the nursing child up to six months of age are satisfied with the breast milk of a healthy and well-nourished mother. In the case of malnourished lactating mothers, it is recommended that the deficiencies in the mother be corrected in order to improve the composition of the milk. For children who are not breast-fed, the recommendations for vitamins that breast milk substitutes should supply would be those indicated for infants older than six months.

Vitamin A

Hypovitaminosis A is prevalent in certain sectors of the Latin American population. In these sectors, in addition to insufficient dietary content, there exist factors that reduce the bioavailability of vitamin A and carotenes, such as intestinal parasitism, diarrhoea, and diets very low in fat.

The concentration of vitamin A suggested for the family diet is 300 retinol equivalents (RE) for each 1,000 kcal.

Vitamin A in the diet provides retinol (preformed vitamin A) and various carotenes that are pro-vitamin A. Retinol is found only in foods of animal origin, especially liver, whole milk, and eggs. Certain dark yellow vegetables, dark green leaves, and yellow fruits, such as papaya and mango, and some varieties of yellow corn are good sources of carotene.

By virtue of the fact that the biological utilization of retinol is superior to that of carotenes, it is advantageous for part of the activity of vitamin A to be provided by this source. Moreover, information about the vitamin value of different carotenes is scarce and may be overestimated.

Ascorbic acid

Ascorbic acid, in addition to functioning in intermediate metabolism, encourages the absorption of iron, especially that of vegetable origin, which predominates in many Latin American diets. As a consequence, as is discussed in the section "Minerals" below, vitamin C should be ingested along with foods that contain iron.

The proposed level for ascorbic acid in the family diet is based on a concentration of the nutrient of 20 mg per 1,000 kcal. When this is computed in terms of daily dietary supply for a man with an energy need of 3,000 kcal per day, it results in a recommendation of 60 mg of vitamin C per day. This recommendation is based on a reanalysis of available biochemical and physiological information, which indicates that with a dietary supply of 60 mg per day, a stabilization or "plateau" is reached in the concentration of ascorbic acid in the leucocytes, and that the renal threshold for the excretion of ascorbic acid is surpassed with higher ingestions.

Because ascorbic acid is destroyed by heat in the presence of oxygen, one can overestimate the quantity of the vitamin provided by foods that are eaten in a cooked form. For this reason fruits that are eaten raw and fresh are the most dependable sources of ascorbic acid. A wide variety of cultivated and wild fruits are good sources of vitamin C, particularly citrus fruits, papaya, hew, mango, and guava. Some vegetables such as broccoli, spinach, and other green leaves also supply appreciable quantities. Among roots and tubers, potatoes and yucca are particularly important sources of this vitamin in populations in which they are consumed in abundance. However, the vitamin is destroyed by dehydration.

Folates

It is proposed that the family diet should provide folates in a concentration of 75 µg per 1,000 kcal. This level is sufficient for all ages and sexes, with the frequent exception of pregnant lactating women. An FAO/WHO committee of experts in 1985 recommended, as a safety measure, a daily intake of 350 µg during pregnancy and 270 µg during lactation. Customary diets in Latin America often do not provide this quantity of folates, and unless they can be improved, it is necessary to supplement them with additional quantities of this vitamin, especially in pregnancy.

A good many foods of animal and vegetable origin contain folates. The best sources of the vitamin include meats, particularly liver, whole grains, leafy vegetables, and most fruits. These folates are sensitive to heat. Therefore, diets containing only cooked foods are potentially poor in this vitamin. This should be taken into account when cow's milk is subjected to strong boiling for hygienic reasons. For the same reason, powdered milks contain minimal quantities of this vitamin.

Thiamine, riboflavin, and niacin

The calculation of the daily supply of thiamin, riboflavin, and niacin on the basis of their concentration per 1,000 kcal has been accepted practice for many years. The figures suggested here are at least 0.4 mg of thiamine, 0.6 mg of riboflavin, and 7 mg of niacin per 1,000 kcal. These levels are satisfactory in covering the needs of any age and physiological state.

Among foods especially rich in thiamine are whole or enriched grains, nuts, and legumes. Vegetables, roots, tubers, and fruits supply moderate quantities, as do pork and some organ meats. It is necessary to emphasize the susceptibility of thiamine to degradation by heat in an alkaline medium. For this reason the practice of adding bicarbonate to water during cooking is undesirable.

The best sources of riboflavin are milk and its derivatives, eggs, liver, and leafy vegetables. Although grains are not particularly rich in the vitamin, they constitute an important source in many diets because of their high consumption. This is even greater when the grains are not highly refined.

The tryptophan of proteins can be metabolically transformed to niacin by the human organism. It is estimated that approximately 60 mg of tryptophan give rise to 1 mg of niacin. For this reason, a food may be a good source of niacin or niacin equivalents if it contains appreciable quantities of preformed niacin, tryptophan, or both. When tryptophan is the limiting amino acid in the diet, it is recommended that the dietary supply of niacin be calculated only on the basis of preformed vitamin. Peanuts, legumes, meats, fish, eggs, and milk products are good sources of niacin equivalents because of their high content of tryptophan. Grains supply important quantities of niacin because of the large quantities in which they are ordinarily consumed. In corn, niacin is chemically linked in a form composite that is absorbed poorly by the human intestine. The treatment of corn with an alkali and heat, as is common in Mexico and Central America in the preparation of tortillas, frees the vitamin and makes tryptophan more available. The cleaning and refining of grain reduces its niacin content significantly.

Vitamin supply in situations of low energy intake

When the energy intake of adults and adolescents falls below 2,000 kcal per day, their vitamin needs do not decrease proportionally. Therefore, a minimum intake of vitamins must be maintained corresponding to that recommended for 2,000 kcal per day. This situation presents itself most frequently in persons of advanced age and in those who are excessively sedentary or are undertaking weight-loss diets.

Vitamin supplements

There is no evidence that any benefit can be derived from the consumption of vitamin supplements above the suggested daily dietary supplies. It is to be noted, furthermore, that excessive ingestion of vitamins A and D and, in certain cases, of niacin can result in toxicity. Similarly, the repeated consumption of high doses of ascorbic acid does not have health benefits. It gives rise to high urinary concentrations of oxalates, which can produce renal calculi. Consequently, supplements and "megadoses" of vitamins should not be used indiscriminately, but rather be reserved exclusively for well-defined clinical situations and be taken under medical supervision. In addition, the unnecessary use of vitamin supplements or megadoses represents a waste of economic resources. In poor families, this reduces the capacity to acquire foods beneficial to the health of the whole family.

Fortification and enrichment of foods

Where hypovitaminosis is highly prevalent in particular countries or population groups, it is necessary to consider the convenience or necessity of enriching or fortifying some food vehicles with vitamin A and vitamin D. However? these actions should be temporary in order to resolve the existing problem. When dietary, socio-economic, and ecological conditions permit, these measures should be supplanted by the rational use of foods and diets.

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