Muscle-based food items from farm animals, poultry, and fish contribute significantly to the human intake of essential nutrients (protein, long chain n-3 fatty acids, several trace elements, and most B vitamins) worldwide. The contribution of a food item to the intake of a particular nutrient in a given environment depends on both its level of consumption and its composition.
Meat, poultry, and fish contribute relatively more to the human intake of protein than calories. In intensive production systems, the body fat content of farm animals has decreased considerably by quantitative genetics selection and optimization of feeding. This has resulted in a concomitant reduction in intramuscular lipid content, which is now generally less than 5% in farm animals, whereas the lipid content of muscle from fish is much more variable. On the other hand, storage fat depots are extensively used in meat processing, thereby contributing largely to the total supply of fat from meat-producing animals.
The dietary fatty acid composition has a large impact on the fatty acid composition of muscle and fat tissue in both farm animals and fish, but metabolism controls the extent of modification towards a species-specific fatty acid profile (e.g., a higher conservation of n-6 and long chain n-3 polyunsaturated fatty acids in terrestrial animals and fish respectively). Nevertheless, several fold differences in the long chain n-3 fatty content of tissues may be observed.
The extent to which the content of other micronutrients in animal tissues is responsive to dietary or other strategies depends on metabolic regulation and needs to be evaluated case by case (e.g., selenium and iodine contents in muscle are much more responsive to increasing concentrations in the diet than copper, iron, manganese, and zinc).
Cost-benefit analyses are required encompassing all levels of the livestock and aquaculture chain for evaluating the human health impact of altering the nutrient composition of animal-derived foods and the efforts and natural resources needed for this purpose, versus alternative strategies.