Fatty Acids in Infant Development

Importance of breastfmilk DHA and AA
Long-chain polyunsaturated fatty acids (LCPs) are essential components of infant nutrition. The LCPs arachadonic acid (AA) and decosahexanoic acid (DHA) are currently attracting a considerable amount of attention due to their pivotal role in development. DHA is essential for retinal and nervous system development. AA is necessary for growth and ecosanoid synthesis (regulators of homeostasis and response to injury). Both LCPs are important constituents of neuronal membranes and blood vessels in the brain. If severe deficiencies of these fatty acids occur, symptoms such as poor growth, skin lesions, degenerative changes in internal organs, abnormal visual function and peripheral neuropathy are observed.

LCPs can be obtained directly from breastmilk but they are absent in the commercial formula sold in most countries. Adults are capable of synthesizing AA and DHA from their essential fatty acid precursors: AA is synthesized from the omega-6 essential fatty acid linoleic acid (LA) and DHA is synthesized from linolenic acid (ALA), an omega-3 essential fatty acid. Infants, however, are not capable of producing sufficient LCPs to meet their full nutritional requirements therefore the supply obtained from breastmilk is crucial. Studies show that breastfed infants have increased amounts of DHA in brain tissue and blood as well as superior visual acuity, an indication of neurological development.

Formula fats inadequate
Artificially fed babies must rely on inadequate endogenous synthesis of DHA and AA from the LA and ALA obtained from formula. LCP synthesis is further compromised by the imbalance of LA and ALA in formula. The relative quantities of these fatty acids affect the efficiency of their conversion to AA and DHA because they compete for the same enzyme pathways; if one precursor is more prevalent in the diet it will affect the amount of LCPs produced down the biosynthetic line. In fact, all members of the omega-3 and-6 families interact in complex ways. The inappropriate ratio of LA to ALA in formula creates conditions of LCP deficiency and excess in which one fatty acid can replace another in membranes and tissues. Since they have different biological roles, this can lead to functional abnormalities in infancy and beyond.

Consequences of deficiencies
Short term consequences of LCP deficiency and imbalance caused by artificial feeding have been observed in infants such as inferior visual acuity and reduced sensitivity of rod photoreceptors,(4) sleep pattern disturbances and changes in spontaneous heart rate variability, which is a marker for brain maturation.(1) Long term health consequences of impaired nutrition in infancy are now also being linked. In children, there is evidence that those who were formula fed have inferior cognitive function and visual maturation,(1,4) higher body fat, weight and systolic blood pressure and increased incidence of respiratory illness. In adulthood, studies are beginning to show an association between formula-feeding, lipid abnormalities and a higher incidence of neurodegenerative(4) and vascular diseases.

Research cannot replicate
A large body of research has focused on the attempt to improve infant formula. One area of study is the LA to ALA ratio in artificial milk. The goal is to raise DHA status in formula fed infants to the level of breastfed infants by manipulating these ratios. Studies show the highest levels of DHA in the bloodstream are obtained with the lowest ratios. While these low ratios are superior as far as circulating DHA is concerned, AA status is compromised and functional consequences such as decreased growth are observed as a result. It should be noted that no ratios studied produce DHA levels comparable to breastmilk. The latest focus in fatty acid research is the fortification of infant products with direct sources of DHA and AA, such as are found in breastmilk. Studies thus far have shown circulating DHA levels on par with breastfed babies.(2) Does this overcome the inadequacies of formula as far as fatty acids are concerned? Many problems exist for the DHA-supplemented infant. The safety of LCP sources such as marine oils have been questioned and their optimum quantities have yet to be determined. How the added fatty acids will interact with LA:ALA ratios and other members of the omega families is unknown. The chemical formula of DHA from artificial sources may not be the same as DHA found in breastmilk, therefore absorption and interaction characteristics may be remarkably different.

While researchers fiddle with the balance of fatty acids in infant formula, and deal with the additional uncertainties of the complex cascade of interactions that each adjustment provokes within the omega families, breastmilk will always be the simple, perfectly balanced source of each essential nutrient. And while researchers try to manipulate formula, infants participating in the trials are subjected to experimental nutrition during a critical developmental period. As a result they may never achieve their optimal cognitive and neurological potential. After all, they may be unlucky enough to be chosen for the cohort receiving the least successful formula.

Many years and vast amounts of funding dollars have been dedicated in attempts to bring the nutritional value of fatty acids in formula up to the standards of breastmilk, yet it always falls short in comparison. And fatty acids are only a few of the countless essential nutrients required to nourish an infant. No adequate replacement for human milk can be engineered; the biological complexity of breastmilk defies industrial synthesis.

References:
1.Uauy, R. et al. Role of essential fatty acids in the function of the developing nervous system. Lipids 31:S167-S176,1996 BACK

2. Makrides, M. et al. Are long-chain polyunsaturated fatty acids essential nutrients in infancy? Lancet 345:1463-1468,1995 BACK

3. Lands, W.E.M. Biochemistry and physiology of n-3 fatty acids. FASEB 6:2530-2536,1992

4. Farquharson, J. et al. Effect of diet on the fatty acid composistion of the major phospholipids of infant cerebral cortex. Arch Dis Child 72(3):198-203,1995 BACK

5. Wilson, A.C. et al. Relation of infant diet to childhood health: Seven year follow up of cohort of children in Dundee infant feeding study. BMJ 316:21-23,1998

6. Crawford, M.A. et al. Are deficits of arachadonic and docosahexanoic acids responsible for the neural and vascular complications of preterm babies? Am J Clin Nutr 66(suppl)1023S-1041S,1997

7. Carlson, S.E. Functional effects of increasing omega-3 fatty acid intake. J. Pediatr 131(2):173-175,1997

8. Carlson, S.E. Lessons learned from randomizing infants to marine oil-supplemented formulas in nutrition trials. J Pediatr 125:S33-38, 199