1. The oxidation rates of lauric, myristic, palmitic, stearic, oleic, a-linolenic, linoleic, y-linolenic, dihomoy-linolenic and arachidonic acids were studied by use of a radioisotope tracer technique in weanling rats at rest in a metabolism chamber over 24 h.2. Of the saturated fatty acids, lauric acid (12:O) was the most efficient energy substrate: the longer the chain length of the saturated fatty acids, the slower the rate of oxidation.3. Oleic acid (18: 1) was oxidized at a remarkably fast rate, similar to that of lauric acid. 4.Of the w6 essential fatty acids studied, linoleic acid (18:2w6) was oxidized at a faster rate than any of its 5.The rate of oxidation of y-linolenic acid (18: 3w3) was almost as fast as that of lauric and oleic acids. metabolites, with arachidonic acid (20: 4w6) being oxidized at the slowest rate.Triglycerides serve as a major component of energy intake in the human diet in western countries (Rizek et al. 1983). However, the composition of the triglyceride fatty acids vary considerably depending on the nature of foods eaten. Studies of the comparative metabolism of fatty acids in a whole-body system indicated that the cellular uptake and oxidation of long-chain fatty acids varied with the degree of unsaturation (Mead et al. 1956;Coots, 1964;Cenedella & Allen, 1969). Ockner et al. (1972) showed that there were differences in the intestinal absorption of saturated and unsaturated fatty acids and differences were also noted in their level of incorporation into chylomicrons (McDonald et al. 1980). These findings contradict a common assumption that dietary fats are all oxidized at the same rate. Whole-body oxidation rates in animals given radiolabelled fatty acids have yielded inconsistent findings, since laboratories have used different models and procedures and have studied different fatty acids. The present study was therefore carried out to investigate the difference in rates of whole-body oxidation of medium-chain fatty acids and essential polyunsaturated fatty acids in one model system. Using radioactively labelled substrates, the oxidation rates of lauric, myristic, palmitic, stearic, oleic, linoleic, y-linolenic, dihomoy-linolenic, arachidonic and a-linolenic acids were determined in weaned rats by measuring the extent of labelling in expired 14C0, over 24 h. M E T H O D S A N D MATERIALS AnimalsFor the early part of the experiment, Sprague-Dawley female rats of the CFY strain were bred in the Nuffield Laboratory and, after weaning at 21 d, were used for the metabolism experiment. However, at a later date weanling rats of the same genetic strain as those bred in the Laboratory were obtained from Benton and Kingmon (Yorkshire), since it proved to be more convenient.The rats were kept under controlled conditions with a 12 h light-12 h dark cycle (06.00-18.00 hours light), a temperature range of 19-23' and relative humidity of about 55%. All rats were allowed free access to food (Special Dietary Services, London) and tap water at all times. Rats used for the metabolism experiments ...

No abstract

No abstract

The African savanna ecosystem of the large mammals and primates was associated with a dramatic decline in relative brain capacity associated with little docosahexaenoic acid (DHA), which is required for brain structures and growth. The biochemistry implies that the expansion of the human brain required a plentiful source of preformed DHA. The richest source of DHA is the marine food chain, while the savanna environment offers very little of it. Consequently Homo sapiens could not have evolved on the savannas. Recent fossil evidence indicates that the lacustrine and marine food chain was being extensively exploited at the time cerebral expansion took place and suggests the alternative that the transition from the archaic to modern humans took place at the land/water interface. Contemporary data on tropical lakeshore dwellers reaffirm the above view with nutritional support for the vascular system, the development of which would have been a prerequisite for cerebral expansion. Both arachidonic acid and DHA would have been freely available from such habitats providing the double stimulus of preformed acyl components for the developing blood vessels and brain. The n-3 docosapentaenoic acid precursor (n-3 DPA) was the major n-3-metabolite in the savanna mammals. Despite this abundance, neither it nor the corresponding n-6 DPA was used for the photoreceptor nor the synapse. A substantial difference between DHA and other fatty acids is required to explain this high specificity. Studies on fluidity and other mechanical features of cell membranes did not reveal a difference of such magnitude between even alpha-linolenic acid and DHA sufficient to explain the exclusive use of DHA. We suggest that the evolution of the large human brain depended on a rich source of DHA from the land/water interface. We review a number of proposals for the possible influence of DHA on physical properties of the brain that are essential for its function.

No abstract