Thirty years ago, fat in the average American diet provided ~42% of total calories. This rate had dropped to ~33 % by 1998. At that rate, and using the example of a middle-aged man of normal weight (A), fat intake would be ~86 g/d, 36% of which is consumed as saturated FA, 42 % as MUFA, and 7 % as PUFA.
The current Acceptable Macronutrient Distribution Range (AMDR) suggests a fat intake range of 20-35 % of total energy. Recently, some authors have discussed ranges up to 40%. The recommendations for individual fatty acid types reflect Adequate Intakes (AI). The latest recommendations suggest consuming mostly MUFA since high PUFA intake tends to result in increased levels of potentially harmful lipid oxidation products. There is definitely general agreement that modern-day nutrition is too high in saturated fatty acids. Because the harmful effects of excessive intake of particular fatty acid types are cumulative, and no threshold exists, no Tolerable Upper Limits (UL) have been set for any of them.
Daily n-3 FA requirements are set at 0.7 % of total calories. In the above example this would correspond to a daily supply of -1.1-1.6 g. Actual intakes usually reach these levels; however, recently many authors have considered "optimal" n-3 fatty acid intakes to be higher. The actual n-6 FA to n-3 FA intake ratio is -10:1. In order to attain the target 5:1 ratio, it is recommended to significantly increase wild ocean fish intake and consume a lot more n-3-rich (i. e., green) vegetables. High levels of a-linolenic acid are also found in flax-seed oil. For other foodstuffs, new options for enrichment with n-3 FA are targeted feeding (e. g., poultry) or genetic engineering (e. g., oil seed crops). However, possible consequences of a one-sided increase in n-3 FA intakes and introduction of such enriched products should be thoroughly investigated.
Unlike n-3 FA deficiency, lack of n-6 FA intake results in clinically apparent deficiency symptoms. The classical, biochemical method for diagnosis of essential FA deficiency is to calculate the ratio of eicosatrienoic acid (20:3; n-9) to arachidonic acid (20:4; n-6). In essential FA deficiency, oleic acid (18:1; n-9) uses the enzymes of the enzyme pathway—resulting in the formation of higher level n-9 homologues that are normally rare. However, since eicosa-trienoic acid is not a suitable substitute for arachidonic acid, eicosanoids cannot be synthesized.
Supplementation of 1-2% of total daily calories as linoleic acid is considered sufficient to relieve this deficiency. In the above example, this would correspond to an intake of 5 g of linoleic acid per day, which can be achieved with 1 tbsp of common, unhydrogenated vegetable oil. According to the expert commission of the FAO/WHO, the n-6 FA requirement during pregnancy and lactation is 5-7 % of total calories.
Optimal intakes of n-3 and n-6 FA cannot be determined at present. It should, however, be emphasized that overall, an increase in PUFA intake and a shift of n-6:n-3 ratios in favor of n-3 FA through increased fish and vegetable consumption (B) are recommended.
Occurrence and Requirements
- A. Actual Supply vs. Recommendations -
Recommended amount 80 g a-Linolenic acid n-6 1.5%
Linoleic acid 11 %
Supply 104 g a-Linolenic acid + DHA n-6 1.5%
Linoleic + arachidonic acid 13%
Example: middle-aged male, 2400 kcal
- B. Fatty Acid Composition
Corn oil Soy oil
Monounsaturated fatty acids
■ Polyunsaturated fatty acids
Was this article helpful?
Studies show obesity may soon overtake tobacco as the leading cause of death in America. Are you ready to drop those extra pounds you've been carrying around? Awesome. Let's start off with a couple positive don't. You don't need to jump on a diet craze and you don't need to start exercising for hours each day.