Nutritional Implications of Replacing Bovine Milk Fat With Vegetable Oil in Infant Formulas (2000)

The nutritional implications of replacing bovine milk fat with vegetable oils in infant formulas are evaluated in this review. Milk fat contains higher levels of trans fatty acids (FAs; a negative health factor), higher levels of conjugated linoleic acid (a positive health factor), higher levels of short-chain FAs (neutral effect), and higher levels of phospholipids and sphingolipids (possibly positive, but further investigation is necessary). Palmitate of vegetable oil is less well absorbed than palmitate of milk fat because of its different location on the glycerol backbone. Nonabsorbed palmitate can be excreted as a calcium soap, and there are suggestions that this may compromise overall calcium balance. Vegetable oils contain higher levels of plant sterols, and these have a neutral effect on cholesterol levels in infants. Infants fed vegetable oil–based formulas do not receive dietary cholesterol and must synthesize it. Studies examining the long-term effects of neonatal dietary cholesterol level on cholesterol metabolism in adult life have yielded mixed results. In some studies, infants fed higher levels of cholesterol had better ability to regulate plasma cholesterol levels in later life, but in others this was not the case. In conclusion, there are presently no contraindications for replacing milk fat with vegetable oils in infant formulas. Because there is a plethora of different bioactive compounds in bovine milk fat and vegetable oil whose biologic roles are still under investigation (several of which are described herein), this issue should continue to be closely monitored. FATS IN INFANT FORMULAS Infant formulas generally contain approximately 50% energy as fat. This lipid is of animal or vegetable origin and is generally a combination of different fats, mixed in proportion to mimic the FA composition of human breast milk. Traditionally, formulas have contained substantial quantities of milk fat, but more recently they have tended to be richer in vegetable oils. The main vegetable oils used are coconut oil, corn oil, soybean oil, palm olein, palm kernel oil, palm oil, high oleic safflower oil, peanut oil, and, in Europe, low–erucic acid rapeseed oil. Vegetable oil–based formulas can contain up to 4% residual milk fat, even if milk powder from skimmed milk is used as a protein source. When milk fat is replaced with vegetable oils in formulas, certain biologically active dietary substances are different. These include minerals and ions (1), antioxidants, water-and fat-soluble vitamins (2), contaminants (3), flavonoids, hormones (4), growth factors, nucleotides (5), carnitine (6), enzymes (7), defense agents (8,9), oligosaccharides (10), ether lipids (11), and phytosterols (12). In this article, the advantages and drawbacks of milk fat (9, 11–14) versus vegetable oil use in infant formula are evaluated regarding their effects on nutritional quality. The main discussion focuses on differences in FA composition, triacylglycerol (TAG) structure, phospholipid (PL) and sphingolipid content, and cholesterol content. Comparisons to breast milk-feeding are included, but it should be emphasized that breast milk-feeding provides the infant with a plethora of additional nutritional and psychological support. Although not the subject of this review, for the interested reader, there are numerous reviews on the potential importance of including long-chain FAs such as arachidonic acid (AA) and docosahexaenoic acid (DHA) in the diets of pregnant mothers and preterm and term infants (15–18). FATTY ACIDS Fat mixes used for infant formulas are designed to yield an FA profile as close as possible to that of human milk, including the two essential FAs, linoleic acid (C18:2 n-6) and α-linolenic acid (C18:3 n-3). Nevertheless, between the two main types of fat mixes, (i.e., vegetable fat– and milk fat–based) there are still some potentially important differences. Some FAs such as short-chain FAs (SCFAs) are present in cow's milk fat at much higher levels than in human milk and vegetable oils. Other FAs are present in bovine and human milk but are absent from vegetable oils—for example, conjugated linoleic acid (CLA). The currently available vegetable oil mixes also contain more C12:0, more C18:1 n-9, slightly more C18:2 n-6 and C18:3 n-3, and less C14:0 and C18:0 than the typical milk fat–based formula (19). Bovine fat also contains odd-chain FAs such as C11:0, C13:0, C15:0, C17:0, C19:0, C21:0, C23:0, and C25:0 (20), the physiological importance of which is unknown. In addition to FA compositional differences between milk and vegetable sources, there are differences in positional distribution on the glycerol backbone that can affect FA absorbability (see section on Triacylglycerol Structure). Between milk fat and vegetable oil mixes, there may also be differences in the types and quantity of bioactive N-acyl ethanolamines and related lipids that bind to CB1/2 receptors, or potentiate the activity of CB-receptor–binding lipids (21,22). Short-Chain Fatty Acids Short-chain FAs are consumed in milk (23). Milk fat contains more SCFAs than vegetable oils, including up to 10% butyrate (C4:0). The C4:0 is present in 30% of the in milk, in the with two long-chain FAs The of the formula on the of milk fat but typical may be C4:0 and in with vegetable oil–based formulas at the much levels of C4:0 and Fatty acid and cholesterol composition of human milk and formulas on milk fat or vegetable SCFAs in milk fat may be an energy for the no regarding health of dietary can be at this because of the of from can be and is to have important biologic effects in the dietary butyrate is absorbed in the and of and if can be to the on of SCFAs from and in the is that to C4:0 as but this not it is not dietary butyrate have effects on the and must be in of butyrate in and some in have used of butyrate and Fatty Acids in vegetable oil mixes from coconut oil used in infant formula can have higher levels of than is in bovine milk and from are to have In and or mixed infant to have the with and in from coconut oil have also to have activity the in have to be more than and more than bovine milk The from infants fed formulas of bovine milk fat, corn oil, and coconut oil have to of and to and not of infants in these to the and quantity of present in the infant formula affect Fatty Acids Vegetable oils are of the essential FAs n-6 and Because of the in the of bovine origin have a of this infant formulas on bovine must include vegetable oils to essential FA The long-chain and are not in used vegetable oils, are they in bovine fat, they are present in human milk. This issue is the subject of in the and the is to reviews (15–18). Fatty Acids Milk fat contains approximately FAs there is in human milk and in vegetable oils in bovine milk fat are and These FAs have in the and of adult may be better absorbed present on the of the glycerol backbone and are or in The or of in cow's milk are not in infants. linoleic acids trans and have the of in the are present in bovine and human but the levels in vegetable oils are milk is to contain fat, from the consumed the In cow's milk, these FAs are of of linoleic acid in the and their to be to fat In infant formulas animal fat, the level is fat, and in infant formulas vegetable oil the level is fat linoleic acids have to the of and in in and numerous have effects as a FA and as a in have also to cholesterol and in Some but not also have to have it was that can be to and to with in and to in and is in to may be from the conjugated Fatty Acids vegetable oils are not used in infant but trans fatty acids have in in the and In milk fat–based formulas, the trans of from of lipids milk fat. milk is richer in than milk. Because of this milk fat–based formulas can contain higher levels of than vegetable oil–based fatty acid in term infant formulas in and and bovine milk vegetable oils, of trans of can be in oils and are is Infants also receive in breast milk. their of and oil such as The level of in human milk with the the In human milk contains an of to a an of in milk. infants breast milk may have an of to or even than that infants. 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This that contained in milk than cholesterol may be important in plasma of and of In studies, cholesterol of formulas not to an of plasma cholesterol in infants. This may be because infants fed less cholesterol have the ability to cholesterol it is that cholesterol to vegetable oil formulas, as a or as a of milk fat, infant plasma cholesterol of cholesterol are less than in infants the formulas are vegetable oil–based or milk and Studies examining the effects of neonatal dietary cholesterol level on cholesterol metabolism in adult life have yielded mixed results. In the should be because this can affect the to dietary fat and In some studies, infants fed higher levels of cholesterol had better ability to regulate cholesterol in later life, and in others this was not the case. there is no for cholesterol from the infant Infant formulas contain 50% energy as fat, of mixes of cow's milk fat and vegetable oils or mixes of vegetable oils milk fat. The of the different are to be as close as possible to human milk FA because of the or the of certain FAs in the different fats, there are some differences in FA composition between milk fat and vegetable oil–based formulas. not a health effect to the differences in SCFAs and The of in milk fat–based formulas have a are still The differences in between cow's milk fat and vegetable oils have no effect on the quantity of energy absorbed from fat and an effect on calcium may be with vegetable oils. These effects on calcium and be important for preterm and further is is presently no that the levels of and sphingolipids in vegetable oils with milk fat be a health to infants. The of cholesterol in vegetable oils and its in human and bovine milk that it may be to vegetable oil–based infant formulas with have that such effect on plasma cholesterol levels and that levels of plasma cholesterol are less in than in the formula is vegetable oil–based or milk Studies on the effect of neonatal dietary cholesterol level on cholesterol metabolism in have results. there is no for cholesterol from the infant but this issue must continue to be with on infant and that can affect cholesterol there are presently no contraindications for replacing milk fat with vegetable oils in infant formulas, but a of lipid in vegetable oil and milk fat, as described in this review, have potential for important physiological effects and should be the of