1 This article is adapted from the first chapter of Fats and oils in human nutrition: report of a joint expert consultation, FAO Food and Nutrition Paper No. 57, 1994.
General conclusions and recommendations of the expert consultation on fats and oils in human nutrition
The role of dietary fats and oils in human nutrition is one of the most important areas of concern and investigation in the field of nutritional science. The findings of investigations on this subject have wide-ranging implications for consumers, health-care providers and nutrition educators as well as food producers, processors and distributors. New evidence concerning the benefits and risks associated with particular aspects of dietary fat is constantly emerging in both the scientific literature and the popular media. At times, controversies about these findings emerge. Sifting through all the claims and counterclaims, incomplete and incompatible studies, and biases and competing interests for the elements of truth and a prudent course of action is a challenge. However, such discrimination is essential because changing views about the effects of dietary fats and oils can profoundly influence the consumption of various foods and, ultimately, health and nutritional status, agricultural production, food processing technologies, food marketing practices and nutrition education.
At the invitation of FAO and the World Health Organization (WHO), an international group of experts in nutrition, public health, food science and technology gathered in Rome from 19 to 26 October 1993 to consider the latest scientific evidence about dietary fats and oils. The experts attending the consultation discussed the many crucial and varied roles that dietary fats and oils have in human nutrition. They considered the intakes of different types and levels of dietary fats and oils and their associated health effects. They reviewed many of the technical factors associated with the production, processing, marketing and utilization of fats and oils. Finally, recommendations about dietary fats and oils were made to assist policy-makers, health-care specialists, the food industry and consumers.
This Joint FAO/WHO Expert Consultation on Fats and Oils in Human Nutrition was part of a continuing series of meetings sponsored by FAO and WHO on nutrition-related topics. It was the second such meeting to have been held on fats and oils; the first was held in 1977. The experts reviewed a wide range of topics, as reflected in the meeting report. Fats and oils in human nutrition: report of a joint expert consultation.
The nature of the evidence varies considerably among the different topics. More scientific information and greater understanding of the complex metabolic interactions that determine nutritional and health status will be necessary before full agreement can be reached on each topic. This is a dilemma which is reflected in the nature of the conclusions and recommendations that emerged from the consultation. Also, since efforts to address one aspect of the relationship between diet and health can affect other aspects as well, care needs to betaken not to overemphasize any single issue to the detriment of others. The recommendations therefore reflect a synthesis and weighing of various concerns. The final conclusions and recommendations are provided below, preceded by a brief note identifying key issues.
Minimum desirable intakes of fats and oils for adults
Adequate amounts of dietary fats are essential for health. In addition to contributing to meeting energy needs, intakes of dietary fat must be sufficient to meet requirements for essential fatty acids and fat-soluble vitamins. The minimum intake consistent with health varies throughout a person's life and among individuals. Adequate intake of dietary fat is particularly important prior to and during pregnancy and lactation. Increasing the availability and consumption of dietary fats is often a priority for overcoming the problems of protein-energy malnutrition. Recommendations to populations concerning desirable ranges of fat intakes may vary according to prevailing conditions, especially dietary patterns and the prevalence of diet-related noncommunicable diseases.
· For most adults, dietary fat should supply at least 15 percent of their energy.
· Women of reproductive age should consume at least 20 percent of their energy from fat.
· Concerted efforts should be made to ensure adequate consumption of dietary fat among populations where less than 15 percent of the dietary energy supply is from fat.
Minimum desirable intakes of fats and oils for infants and young children
Both the amount and quality of dietary fat consumed can affect child growth and development. These influences are mediated through energy levels and through the action of specific fatty acids and various non-glyceride components of the fat. From 50 to 60 percent of energy provided from breast milk is from fat, and during the weaning period (i.e. the transition from full breast-feeding to no breast-feeding) care needs to be taken to prevent dietary fat intakes from falling too rapidly or below the required levels. The use of fat, especially vegetable oils, in the foods fed to weanling infants and young children is an effective way to maintain the energy density of their diets.
The consumption of adequate amounts of essential acids is also important for normal growth and development. Arachidonic acid and docosahexaenoic acid (DHA) are particularly important for brain development, and breast milk is a good source of these fatty acids. Preterm infants who had an insufficient intra-uterine supply of arachidonic acid and DHA and who are born with low fat reserves have particular problems.
· Infants should be fed breast milk if at all possible.
· The fatty acid composition of infant formulas should correspond to the amount and proportion of fatty acids contained in breast milk.
· During weaning and at least until two years of age, a child's diet should supply 30 to 40 percent of energy from fat and should provide essential fatty acids at levels similar to those in breast milk.
Vegetable oils, such as oil made from sunflower seeds, are sources of unsaturated fats - Les huiles végétales, telles que l'huile de graines de tournesol, sont une source de graisses non saturées - Los aceites vegetales, como el de semilla de girasol, son fuentes de grasas insaturadas
Upper limits of dietary fat and oil intakes
Excessive dietary fat intake has been linked to increased risk of obesity, coronary heart disease and certain types of cancer. The mechanisms by which these are linked are complex, varied and in many instances not clearly understood. Elevated levels of serum cholesterol and low-density lipoprotein (LDL) constitute major risk factors for atherosclerosis and coronary heart disease. The degree of risk for these and other factors may vary according to, inter alia, type and level of fatty acid intakes, percentage of energy from total fat, dietary cholesterol, lipoprotein levels, intakes of antioxidants and dietary fibre, activity levels and health status. Low-fat diets are often lower in cholesterol and higher in antioxidants and dietary fibre. Among adults, there is no nutritional advantage to consuming high-fat diets once essential energy and nutrient needs are met.
· Active individuals who are in energy balance may consume up to 35 percent of their total energy intake from dietary fat if their intake of essential fatty acids and other nutrients is adequate and the level of saturated fatty acids does not exceed 10 percent of energy.
· Sedentary individuals should not consume more than 30 percent of their energy from fat, particularly if it is high in saturated fatty acids derived from animal sources.
Saturated and unsaturated fatty acids and cholesterol
The saturated fatty acids - lauric, myristic and, to a lesser extent, palmitic acids - elevate serum cholesterol and LDL levels. Stearic acid does not elevate serum cholesterol or LDL levels, but its other health effects are as yet undefined. Linoleic acid (polyunsaturated) moderately reduces serum cholesterol and LDL levels. Oleic acid (monounsaturated) appears to be neutral in regard to LDL but raises high-density lipoprotein (HDL) modestly. Dietary cholesterol elevates serum cholesterol and LDL levels, but the extent of increase is highly variable.
· Intakes of saturated fatty acids should not provide more than 10 percent of energy.
· It is desirable that intakes of linoleic acid should provide between 4 and 10 percent of energy. Intakes in the upper end of this range are recommended when intakes of saturated fatty acids and cholesterol are relatively high.
· Reasonable restriction of dietary cholesterol (less than 300 mg/day) is advised.
Isomeric fatty acids
Unsaturated vegetable oils are frequently partially hydrogenated to produce more solid, plastic or stable fats. During this process, various cis and trans isomers are formed. Unlike oleic acid, the trans isomers in partially hydrogenated vegetable oils tend to elevate serum LDL levels and may lower HDL levels. High intakes of trans fatty acids are undesirable, but it is not yet certain whether the use of trans or saturated fatty acids is preferable where such fatty acids are required in formulation of food products.
· Consumers should substitute liquid oils and "soft" fats (i.e. those that are soft at room temperature) for "hard fats" (those that are more solid at room temperature) to reduce both saturated fatty acids and trans isomers of unsaturated fatty acids.
· Food manufacturers should reduce the levels of trans isomers of fatty acids arising from hydrogénation.
· Governments should monitor the levels of isomeric fatty acids in the food supply.
· Governments should limit the claims concerning the saturated fatty acid content of foods that contain appreciable amounts of trans fatty acids, and they should not allow foods that are high in trans fatty acids to be labelled as being low in saturated fatty acids.
Substances associated with fats and oils: antioxidants and carotenoids
Substantial evidence indicates that relatively high intakes of fruits and vegetables-sources of various antioxidants, carotenoids and other non-glyceride components-reduce the risk of coronary heart disease and some cancers. However, specific conclusions and recommendations concerning the general health benefits and desirable intakes of these substances cannot be made on the basis of current evidence.
Processing and refining techniques used to eliminate or reduce negative characteristics of edible oils can also lead to the loss of various nutritionally beneficial components such as antioxidants and carotenoids. However, producers can minimize such losses through appropriate processing, refining and storage techniques, and they are encouraged to do so.
Consumption of red palm oil can help prevent vitamin A deficiency - La consommation d'huile de palme rouge peut aider à prévenir la carence en vitamine A - El consumo de aceite de palma roja puede ayudar a evitar la avitaminosis A
· In countries where vitamin A deficiency is a public health problem, the use of red palm oil, wherever readily or potentially available, should be encouraged. If red palm oil is refined, processing techniques that preserve its carotenoid and tocopherol content should be utilized.
· Tocopherol levels in edible oils need to be adequate to stabilize the unsaturated fatty acids present. Therefore, foods high in polyunsaturates should contain at least 0,6 mg tocopherol equivalents per gram of polyunsaturated fatty acid. Higher levels may be necessary for fats that are rich in fatty acids containing more than two double bonds.
Essential fatty acids
The n-6 and n-3 fatty acids in the membrane phospholipids exert their metabolic control through their roles as precursors of various eicosanoids, which are potent and highly reactive compounds. Different eicosanoids have widely divergent, and often opposing, effects on, for example, smooth muscle cells, platelet aggregation, vascular parameters (permeability, contractility), inflammatory processes and the immune system. Since the n-6 and n-3 fatty acids compete for the same metabolic substrates and have different biological roles, the balance between them in the diet can be of considerable importance.
A number of studies have shown that the consumption of foods (such as oil-rich fish) containing the long-chain n-3 fatty acids eicosapentaenoic acid (EPA) and DHA is associated with decreased risk of coronary heart disease, probably because of mechanisms not related to serum lipoprotein levels.
Essential fatty acids are especially important for normal foetal and infant growth and development, and for brain development and visual acuity in particular. In well-nourished women, an average of approximately 2.2 g of essential fatty acids are deposited in maternal and foetal tissues each day throughout pregnancy.
Oil-rich fish provide essential fatty acids - Les poissons riches en huile fournissent des acides gras essentiels - Los pescados de alto contenido oleaginoso proporcionan ácidos grasos esenciales
· The ratio of linoleic to a -linolenic acid in the diet should be between 5:1 and 10:1.
· Individuals with a linoleic: a -linolenic acid ratio in excess of 10:1 in the diet should be encouraged to consume more n-3 rich foods such as green leafy vegetables, legumes, fish and other seafood.
· Particular attention must be paid to promoting adequate maternal intakes of essential fatty acids throughout pregnancy and lactation to meet the requirements of foetal and infant development.
Dietary information and programme needs
Adequate information on nutritional status, dietary intakes and the composition of foods is required for designing and monitoring programmes to improve nutrition, including programmes to promote appropriate intakes of dietary fats and oils.
Governments and health authorities in all countries need to be aware of the escalating risk of non-communicable diseases that follows the adoption of inappropriate dietary practices and less active lifestyles.
· Standard methods and reference materials should be used in the analysis of the fatty acid content of foods and in the preparation of nutrient databases.
· Adequate food composition data on fats should be widely available and accessible, with each food item identified by unambiguous descriptive factors.
· The standard Atwater factor of 9.0 kcal (37,7 kJ) per gram of fat should be used for calculating the energy value of fat in all nutrition surveys and food composition tables.
· Periodic surveys of the weight status (body mass index) of adults are desirable in all countries to help identify trends and populations affected by or at greater risk of undernutrition and diet-related non-communicable diseases and to monitor the impact of interventions.