Food as a Source of Nutrients
Introduction to Food-Based Dietary Guidelines: The purpose of this chapter is to define and discuss the use of food-based guidelines to improve micronutrient intake and status.
- Access to a sufficient quantity and variety of foods should meet the nutritional needs of populations.
- However, sufficient quantities and varieties of foods may not be met in populations where poor socioeconomic conditions limit the ability to produce or purchase food or where cultural practices restrict dietary intake.Dietary guidelines have been used to improve micronutrient intakes. There have been two general approaches to defining dietary guidelines:
- Food-based dietary guidelines (FBDG):
- FBDGs emphasize using a combination of foods to meet the nutritional requirements (rather than focusing on the requirements for a specific nutrient). A healthful diet can be achieved through multiple combinations of foods.
- FBDGs are intended to be practical guidelines to reach nutritional goals in a population and can be used to educate the public on ways to select foods for a healthful and adequate diet.
- FBDGs are based on the fact that people eat food, not individual nutrients.
- FBDGs consider customary dietary practices, the ecological setting for populations, and the socioeconomic and cultural factors. FBDGs then identify where modifications should be made to attain nutritional adequacy.
- Nutrient-based approach:
- This approach to defining dietary guidelines has emphasized the precise amounts of essential nutrients needed to meet biochemical and physiological requirements (e.g., emphasizing the recommended nutrient intakes; RNIs).
- This approach has been important in defining the nutritional public health priorities, but has been too narrowly focused and has not provided practical guidelines to solve the nutritional problems of the world.
- General features of FBDGs:
- Advice for a healthful diet should include descriptions easily understood by individuals and include:
- Quantitative descriptions: the portion size and the number of servings per day
- Qualitative descriptions: the biological utilization of nutrients in the food and the potential interactions of nutrients in the diet which may inhibit or enhance the bioavailability of nutrients from a particular food source
- Adding foods with a high micronutrient density to staple diets will improve micronutrient nutrition. Examples of such foods include pulses or legumes, vegetables (including green leafy vegetables), and fruits.
- Dietary diversification is also important in improving micronutrient nutrition because of the interrelationships between foods. For instance, fruits rich in vitamin C improve the absorption of non-heme iron.
- Young children have greater micronutrient needs relative to their energy needs, and therefore, micronutrient dense foods are important for maintaining adequate nutrition.
- FBDGs need to also educate individuals on proper storage and cooking methods to reduce micronutrient losses.
Examples of Dietary Diversification: Dietary diversification is a feature of FBDGs aimed at improving micronutrient nutrition. The following are examples of how dietary diversification can improve cereal- and tuber- based diets (diets based on rice, corn, wheat, potato or cassava). Cereal- and tuber-based diets are consumed by two-thirds of the global population.
- Most populations with micronutrient deficiencies consume staple diets of refined cereal grain- or tuber-based diets, which often provide adequate protein and energy, but insufficient amounts of micronutrients.
- The following examples include five micronutrients which are considered to be of public health importance and which may be markers of overall micronutrient status. Furthermore, there is a high prevalence of vitamin A, iron, and zinc deficiencies worldwide.
- In general, adding carrots, an orange, beef, spinach, and lentils (or black beans) to the staple diets will meet the recommended nutrient densities for these five micronutrients.
- Vitamin A nutrition will be improved by including:
- A small portion of plant foods rich in carotenoids (the precursor for vitamin A). Examples include:
- Carrots, mangos, papaya, and melon
- Green leafy vegetables (ivy gourd has been used in Thailand)
- Palm oil
- Animal foods, which include the highly bioavailable form of vitamin A. Including small portions of animal foods will exceed the recommended nutrient density for vitamin A.
- Vitamin C nutrition will be improved by including:
- Citrus fruits, including an orange, guava, amla, kiwi, cranberries, strawberries, papaya, mango, cantaloupe, spinach, Swiss chard, tomato, asparagus, or Brussels sprouts.
- Minimal cooking (e.g., steaming or stir-frying) is recommended because ascorbic acid (vitamin C) may be destroyed by heat.
- Folate nutrition will be improved by including:
- The best sources are green leafy vegetables, Brussel sprouts, and organ meats (chicken liver is a great source).
- Legumes (e.g., lentils or beans and peas in larger portions)
- Prolonged heating in water should be avoided as 50% or more of folate is destroyed during cooking. Consuming the cooking water from the vegetables increases folate intake.
- Iron and zinc nutrition will be improved by including:
- Small amounts of flesh food
- Legumes will slightly improve the amount of iron in the diet but will not be adequate unless some meat or fish is included. The form of iron in legumes (non-heme iron) has poor bioavailability.
- Education about enhancers and inhibitors of iron:
- Vitamin C (ascorbic acid) enhances iron absorption.
- Food preparation methods including fermentation of phytate-containing grains during bread baking (e.g., including yeast in the bread), which minimizes the effects of phytates in inhibiting both iron and zinc absorption.
- In addition to improving dietary diversification, proper dietary practices and food preparation methods must to be taught for any food-based approach to be effective. Examples include
- Vegetables rich in vitamin C, folate or other water-soluble or heat labile vitamins need to be minimally cooked with small amounts of water.
- For iron and zinc, increasing the enhancers of absorption and reducing the inhibitors of absorption is important.
Practices to Improve Dietary Diversification on a Community-Wide Level
- Five strategies have been identified to improve dietary diversification and prevent micronutrient malnutrition in populations consuming cereal- or tuber- based diets and who have limited financial resources or limited access to food. These strategies rely on community-wide commitment and include the following (please refer to the text of the chapter for a full description):
- Community or home vegetable and fruit gardens
- Raising of fish, poultry and small animals
- Implementation of large-scale commercial vegetable and fruit production
- Reduction of post-harvest losses of the nutritional value of micronutrient-rich foods, such as fruits and vegetables (e.g., proper storage and effective cooking methods)
- Improvement of micronutrients levels in soils and plants, which will improve the composition of plant foods and enhance yields.
The Role of Fortification and Supplementation
- Food-based strategies to improving nutrition may take longer to implement than supplementation or fortification, but food-based approaches are truly sustainable once in place.
- Fortification and supplementation may be used to complement food-based strategies, especially when food-based approaches are not feasible or still under development.
- The inclusion of small amounts of flesh foods and a variety of fruits and vegetables to staple diets is generally sufficient to provide adequate micronutrient nutrition. However, this is often difficult in communities living in poverty, and food fortification and supplementation strategies may offer effective alternatives.
- Fortification is defined as the addition of a nutrient to a commonly eaten food.
- Supplementation is defined as temporarily or periodically providing large doses of micronutrients in the form of a capsule/tablet or by injection.
- Supplementation is only recommended for groups who are not able to meet their nutritional requirements through food.
Conclusions on Food-Based Dietary Guidelines
- FBDGs are an approach to nutrition and food policies aimed at health promotion and disease prevention.
- Examples of FBDGs across countries include the use of food pyramids, rainbows, dishes, or pots.
- The general recommendation of FBDGs is that nutritionally adequate diets include a variety of foods and should be primarily plant-based with small amounts of flesh foods.
- Plant-based diets need to contain a variety of fruits and vegetables, pulses or legumes, and minimal amounts of processed starchy staple foods.
- Small amounts of animal foods need to be included to provide additional nutrients to plant-based foods.
- These dietary guidelines are the same for addressing the problem of micronutrient malnutrition as well as over-nutrition (e.g., obesity).Local diets, the food preparation and storage methods, and typical food combinations which may affect bioavailability and utilization need to also be considered on the population level when making FBDGs.
Reference: Food as a source of nutrients. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004: 318-337.