Importance of defining food-based recommendations

17.1 Importance of defining food-based recommendations

Dietary patterns have varied over time. Changes in these patterns are dependent on such things as agricultural practices and climatic, ecologic, cul- tural, and socioeconomic factors, which in turn, determine which foods are available. At present, virtually all dietary patterns show that the nutritional needs of population groups are adequately satisfied or even exceeded. This is true except where socioeconomic conditions limit the capacity to produce and purchase food or aberrant cultural practices restrict the choice of foods. It is thought that if people have access to a sufficient quantity and variety of foods, they will meet, in large part, their nutritional needs. However, for certain groups of people because of economic restrictions, levels of certain micronu- trients may not be met from food alone. Thus, micronutrient adequacy must

be included in evaluating the nutritive value of diets alongside energy and protein adequacy.

A healthful diet can be attained through the intake of multiple combina- tions of a variety of foods. Given this, it is difficult to define the ranges of intake for a specific food, which should be included in a given combination with other foods to comply with nutritional adequacy. In practice, the set of food combinations which provide nutritional adequacy are limited by the level of food production sustainable in a given ecological setting. In addition, there are economic constraints that limit food supply at the household level. The development of food-based dietary guidelines (FBDGs) (1) recognizes this and focuses on how a combination of foods can meet nutrient require- ments rather than on how each specific nutrient is provided in adequate amounts.

The first step in the process of setting dietary guidelines is defining the sig- nificant diet-related public health problems in a community. Once these are defined, the adequacy of the diet is evaluated by comparing the information available on dietary intake with the established recommended nutrient intakes (RNIs). Nutrient intake goals are specific for a given setting, and their purpose is to promote overall health, control specific nutritional diseases (whether

17. FOOD AS A SOURCE OF NUTRIENTS

they are induced by an excess or deficiency of nutrient intake), and reduce the risk of diet-related multifactorial diseases. Dietary guidelines represent the practical way to reach the nutritional goals for a given population. They take into account customary dietary patterns and indicate what aspects of each should be modified. They consider the ecological setting in which the popu- lation lives, as well as the socioeconomic and cultural factors that affect nutri- tional adequacy.

The alternative approach to defining nutritional adequacy of diets relies on the biochemical and physiological basis of human nutritional requirements in health and disease. The quantitative definition of nutrient needs and its expression as RNIs have been important instruments of food and nutrition policy in many countries and have focused the attention of international bodies on this critical issue. This nutrient-based approach has served many purposes but has not always fostered the establishment of nutritional and dietary priorities consistent with the broad public health priorities at the national and international levels. It has permitted a more precise definition of requirements for essential nutrients but unfortunately has often been too nar- rowly focused, concentrating on the precise nutrient requirement amount, and not on solving the nutritional problems of the world.

In contrast to RNIs, FBDGs are based on the fact that people eat food, not nutrients. Defining nutrient intakes alone is only part of the task of dealing with nutritional adequacy. As will be illustrated in this chapter, the notion of nutrient density is helpful for defining FBDGs and evaluating the adequacy of diets. However, unlike RNIs, FBDGs can be used to educate the public through the mass media and provide a practical guide to selecting foods by defining dietary adequacy (1).

Advice for a healthful diet should provide both a quantitative and qualitative description of the diet for it to be understood by individuals, who should be given information on both size and number of servings per day. The quantitative aspects include the estimation of the amount of nutrients in foods and their bioavailability in the form they are actually consumed. Unfortunately, available food composition data for most foods currently consumed in the world are incomplete, outdated, or insufficient for evaluating true bioavailability. The qualitative aspects relate to the biological utilization of nutrients in the food as consumed by humans and explore the potential for interaction among nutrients. Such an interaction may enhance or inhibit the bioavailability of a nutrient from a given food source.

The inclusion of foods in the diet which have high micronutrient density— such as pulses or legumes, vegetables (including green leafy vegetables), and

VITAMIN AND MINERAL REQUIREMENTS IN HUMAN NUTRITION

fruits—is the preferred way of ensuring optimal nutrition, including micronu- trient adequacy, for most population groups. Most population groups who are deficient in micronutrients subsist largely on refined cereal grain- or tuber- based diets, which provide energy and protein (with an improper amino acid balance) but insufficient levels of critical micronutrients. There is a need for

a broadening of the food base and a diversification of diets. Figures 17.1–17.4 illustrate how addition of a variety of foods to four basic diets (i.e. a white rice-based diet; a corn-tortilla-based diet; a refined couscous-based diet; and a potato-based diet) can increase the nutrient density of a cereal- or tuber-based diet. Adding reasonable amounts of these foods will add micronutrient density to the staple diet and in doing so could reduce the prevalence of diseases resulting from a micronutrient deficiency across pop- ulations groups.

The recent interest in the role of phytochemicals and antioxidants on health, and their presence in plant foods, lends further support to the recom- mendation for increasing the consumption of vegetables and fruit in the diet. The need for dietary diversification is supported by the knowledge of the interrelationships of food components, which may enhance the nutritional value of foods and prevent undesirable imbalances which may limit the utilization of some nutrients. For example, fruits rich in ascorbic acid will enhance the absorption of non-haem iron.

If energy intake is low (<8.368MJ/day), for example, in the case of young children, sedentary women, or the elderly, the diet may not provide sufficient amounts of vitamins and minerals to meet RNIs. This situation may be of special relevance to the elderly, who are inactive, have decreased lean body mass, and typically decrease their energy intake. Young children, pregnant women, and lactating women who have greater micronutrient needs relative to their energy needs will also require an increased micronutrient density.

The household is the basic unit in which food is consumed in most set- tings. If there is sufficient food, individual members of the household can consume a diet with the recommended nutrient densities (RNDs) and meet their specific RNIs. However, appropriate food distribution within the family must be considered to ensure that children and women receive adequate food with high micronutrient density. Household food distribution must be con- sidered when establishing general dietary guidelines and addressing the needs of vulnerable groups in the community. In addition, education detailing the appropriate storage and processing of foods to reduce micronutrient losses at the household level is important.

17. FOOD AS A SOURCE OF NUTRIENTS

FIGURE 17.1

Impact of the addition of selected micronutrient-rich foods to a white rice-based diet on the recommended nutrient density (RND) of vitamin A, vitamin C, folate, iron (Fe) and zinc (Zn)

a. White rice-based diet

% RND 80 60 40 20

Vit A Vit C Folate

Fe Zn

b. White rice + carrots c. White rice + carrots and an orange

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

d. White rice + carrots, an orange e. White rice + carrots, an orange and lentils

and beef

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

f. White rice + carrots, an orange, beef g. White rice + carrots, an orange, beef, and spinach

spinach and lentils

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

VITAMIN AND MINERAL REQUIREMENTS IN HUMAN NUTRITION

FIGURE 17.2

Impact of the addition of selected micronutrient-rich foods to a corn-tortilla-based diet on the recommended nutrient density (RND) of vitamin A, vitamin C, folate, iron (Fe) and zinc (Zn)

a. Corn-tortilla-based diet

% RND 80 60 40 20

Vit A Vit C Folate

Fe Zn

b. Corn-tortilla + carrots c. Corn-tortilla + carrots and an orange

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

d. Corn-tortilla + carrots, an orange e. Corn-tortilla + carrots, an orange and lentils

and beef

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

f. Corn-tortilla + carrots, an orange, beef g. Corn-tortilla + carrots, an orange, beef, and spinach

spinach and black beans

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

17. FOOD AS A SOURCE OF NUTRIENTS

FIGURE 17.3

Impact of the addition of selected micronutrient-rich foods to a refined couscous-based diet on the recommended nutrient density (RND) of vitamin A, vitamin C, folate, iron (Fe) and zinc (Zn)

a. Refined couscous-based diet

% RND 80 60 40 20

Vit A Vit C Folate

Fe Zn

b. Refined couscous + carrots c. Refined couscous + carrots and an

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

d. Refined couscous + carrots, an orange e. Refined couscous + carrots, an orange and lentils

and beef

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

f. Refined couscous + carrots, an orange, g. Refined couscous + carrots, an orange, beef and spinach

beef, spinach and black beans

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

VITAMIN AND MINERAL REQUIREMENTS IN HUMAN NUTRITION

FIGURE 17.4

Impact of the addition of selected micronutrient-rich foods to a potato-based diet on the recommended nutrient density (RND) of vitamin A, vitamin C, folate, iron (Fe) and zinc (Zn)

a. Potato-based diet

Vit A Vit C Folate

Fe Zn

b. Potato + carrots c. Potato + carrots and an orange

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

d. Potato + carrots, an orange and lentils e. Potato + carrots, an orange and beef

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

f. Potato + carrots, an orange, beef g. Potato + carrots, an orange, beef, and spinach

spinach and lentils

Vit A Vit C Folate

Fe Zn

Vit A

Vit C Folate Fe Zn

17. FOOD AS A SOURCE OF NUTRIENTS