Know Your Macronutrients: Fats
- 9 January 2025


Introduction
Dietary fat is one of three macronutrients (components of foods that are broken down and absorbed by the body to support the maintenance of life) in the human milk and infant formula and is fundamentally important for infant growth and development. Dietary fat is an important energy source for infants, and it also impacts the development of major organs and organ systems including, but not limited to, the central nervous system, the immune system, the cardiovascular system, gastrointestinal system, and endocrine system.1 Dietary fat is also essential for helping the body absorb fat-soluble vitamins such as Vitamin A, D, E, and K.
Fatty acids are the building blocks of triglycerides (which are the main constituents of dietary and body fat). The positioning of fatty acids on the triglyceride structure has implications on infant gastrointestinal and musculoskeletal health outcomes. To learn more, see the ‘Dietary Fat Fast Facts’ box for more detailed information about the triglyceride structure and the importance of fatty acid positioning.
Dietary fat is classified as either unsaturated (liquid at room temperature) or saturated (solid at room temperature). Unsaturated fat is further characterized as monounsaturated or polyunsaturated. Omega-3 and omega-6 polyunsaturated fatty acids are considered essential, meaning that our bodies cannot synthesize these and we must therefore consume them in our diets. DHA, EPA, ARA, and ALA are sources of polyunsaturated fatty acids.
Saturated fats are found in foods such as animal products including meat, fatty fish, whole milk and whole milk dairy products, eggs, butter, and non-animal products such as oils from coconuts and palm fruits. Unsaturated fats are found in foods like fatty fish, nuts and seeds, oils (e.g., olive, safflower, canola) and grass-fed meat and dairy products. Infants also consume dietary fats in human milk and infant formula. Human milk contains fats like palmitic acid and cholesterol, and formula provides fats from sources like whole milk and vegetable oils.
FDA Requirements
The United States Food and Drug Administration (FDA) maintains dietary fat requirements of 3.3 g/100 kcal (30% calories) with a maximum of 6 g/100 kcal (54% calories) in infant formula.2 While the FDA establishes strict criteria for dietary fat quantities, infant formula companies have relative freedom in the sources of dietary fat in commercially available products. In other words, not all infant formulas are the same. As long as quantitative dietary fat requirements are represented in appropriate amounts in the final product, infant formula companies can determine whether to prioritize dietary fat from various sources like bovine whole milk (grass- or grain-fed), non-bovine milk, vegetable and seed oils, and more. An understanding of the bioactive roles, and processing effects of dietary fat sources on infant health, further guides the ingredient selection process.
Dietary Fat for Infant Health: A Shift in Paradigm
Historically, dietary fat has faced intense public health scrutiny due to concerns about perceived negative health outcomes.3 More recent discoveries in human milk science allow for a shift in the understanding of the foundational role of dietary fats on health outcomes, including key benefits for infant growth and development.
Mature human milk contains ~3-5% (35-40 g/L) fat (although fat content is the most variable component of human milk and depends on the stage of lactation, time of day, and individual characteristics of the mother) and provides a major source of energy for infants.4 The majority of fats (>95%) in human milk are present as triglycerides packaged in milk fat globule membrane (MFGM). The main purpose of MFGM is to deliver fatty acids to the infant; however, components of MFGM have also been shown to offer cognitive, immune, metabolic, and gastrointestinal benefits.5,6 MFGM is also found in bovine milk and infant formula companies using whole bovine milk retain more naturally occurring MFGM. However, infant formula using skimmed milk has had MFGM removed so some infant formula companies using skimmed milk have begun to add MFGM components to their products.6
Omega-3 and omega-6 polyunsaturated are essential fatty acids that cannot be made in the body and therefore must be consumed in the diet.7 These fatty acids are important for many health-related outcomes, including infant brain and nerve cell development.8 Optimal omega-6 to omega-3 ratios for infants remain controversial; however, some studies have shown beneficial outcomes with respect to cognition and visual acuity with a slightly higher ARA (an omega-6) to DHA (an omega-3) ratio.9,10 Vegetable, seed, and/or fruit oils are necessary ingredients for formula-fed infants in order to mirror the average fatty acid composition found in human milk known to support growth and development. Rapeseed, for example, has a balance of fatty acids, a preferred ratio of omega 3 to omega 6, and is high in oleic acid (mimicking levels in human milk).11 Something to be mindful of is how the extraction methods and processing of oils can impact ingredient integrity and oxidation associated with potentially harmful peroxides. Some formula companies choose to use organic oils that are low in erucic acid, non-GMO, and processed using low-heat extraction methods (non-hexane extraction), whereas others do not.12 Although these oils are necessary to include in infant formula, the use of whole milk lessens the reliance on seed oils to meet fatty acid requirements.
Nutrient Spotlight: Palmitic Acid
Analysis of human milk reveals that over 40% of the fat content in human milk is composed of saturated fat.13 Palmitic acid is a key saturated fatty acid in human milk, comprising 15-25% of total fatty acids. Palmitic acid can be esterified on the glycerol backbone in one of three positions. Palmitic acid in the SN-2 position makes up 70-88% of the total fatty acids in human milk14 (See the ‘Fast Facts’ box for a visual representation of how fatty acids can be esterified on the glycerol backbone at the SN-1, SN-2, or SN-3 position).
Palmitic acid in the SN-2 position offers functional health benefits for infants including improved nutrient absorption of calcium, resulting in softer stools and appropriate bone development.15 On the other hand, palmitic acid in the SN-1 and SN-3 positions is known to form calcium palmitate soaps, contributing to harder stools, fecal calcium loss, and constipation.16–18 Whereas palm oil is a common ingredient in infant formula, it provides palmitic acid in the SN-1 and SN-3 positions, sources of palmitic acid in infant formula from whole cow’s milk, contains 40% of the total fatty acids in the SN-2 position (compared to vegetable oil at 7-20%).14
Relevance For Your Clinical Practice
In order to give evidence-based infant formula advice and recommendations to families in your practice, it is important to understand the potential health implications of different nutrients found in commercially available products. Here are important health outcomes associated with some of the ingredients discussed:
Associated with softer stools, likely driven by the higher percentage of palmitic acid in the SN-2 position.15
Associated with harder stools when studied as a component of infant formula, likely due to the formation of calcium soaps in the intestines.18
Necessary ingredients in infant formula to achieve the fatty acid profiles known to support growth and development. Extraction and processing methods can impact the final ingredient.12
Saturated fats: Meat, fatty fish, whole milk and whole milk dairy products, eggs, butter, and oils from coconuts and palm fruits.
Unsaturated fats: Fatty fish, nuts and seeds, oils (e.g., olive, safflower, canola) and grass-fed meat and dairy products.
Infants consume dietary fats in human milk and infant formula. Human milk contains fats like palmitic acid and cholesterol, and formula provides fats from sources like whole milk and vegetable, fruit, and seed oils.
Ingredients described here represent a subset of many other factors, including other macronutrients and bioactive factors, that may impact infant health. All ingredients in commercially available infant formula are approved for use by the FDA. Beyond acknowledged health outcomes, infant formula purchasing decisions should be made holistically and with respect to financial means and accessibility, the infant’s tolerance of the product, personal values, and more.
Hardy SC, Kleinman RE. Fat and cholesterol in the diet of infants and young children: implications for growth, development, and long-term health. J Pediatr. 1994;125(5 Pt 2). doi:10.1016/S0022-3476(06)80739-0
21 USC 350a: Infant formulas. Accessed April 10, 2024. https://uscode.house.gov/view.xhtml?req=(title:21%20section:350a%20edition:prelim)
Olson RE. Is it wise to restrict fat in the diets of children? J Am Diet Assoc. 2000;100(1):28-32. doi:10.1016/S0002-8223(00)00012-2
Pietrzak-Fiećko R, Kamelska-Sadowska AM. The Comparison of Nutritional Value of Human Milk with Other Mammals’ Milk. Nutrients. 2020;12(5). doi:10.3390/NU12051404
Kosmerl E, Rocha-Mendoza D, Ortega-Anaya J, Jiménez-Flores R, García-Cano I. Improving Human Health with Milk Fat Globule Membrane, Lactic Acid Bacteria, and Bifidobacteria. Microorganisms. 2021;9(2):1-22. doi:10.3390/MICROORGANISMS9020341
Da Silva RC, Colleran HL, Ibrahim SA. Milk fat globule membrane in infant nutrition: a dairy industry perspective. J Dairy Res. 2021;88(1):105-116. doi:10.1017/S0022029921000224
Kapoor B, Kapoor D, Gautam S, Singh R, Bhardwaj S. Dietary Polyunsaturated Fatty Acids (PUFAs): Uses and Potential Health Benefits. Curr Nutr Rep. 2021;10(3):232-242. doi:10.1007/S13668-021-00363-3
Xiang M, Alfvén G, Blennow M, Trygg M, Zetterström R. Long-chain polyunsaturated fatty acids in human milk and brain growth during early infancy. Acta Paediatr. 2000;89(2):142-147. doi:10.1080/080352500750028735
Birch EE, Carlson SE, Hoffman DR, et al. The DIAMOND (DHA Intake And Measurement Of Neural Development) Study: a double-masked, randomized controlled clinical trial of the maturation of infant visual acuity as a function of the dietary level of docosahexaenoic acid. Am J Clin Nutr. 2010;91(4):848-859. doi:10.3945/AJCN.2009.28557
Drover JR, Hoffman DR, Castañeda YS, et al. Cognitive function in 18-month-old term infants of the DIAMOND study: a randomized, controlled clinical trial with multiple dietary levels of docosahexaenoic acid. Early Hum Dev. 2011;87(3):223-230. doi:10.1016/J.EARLHUMDEV.2010.12.047
Matthaus B, Özcan MM, Juhaimi F Al. Some rape/canola seed oils: fatty acid composition and tocopherols. Z Naturforsch C J Biosci. 2016;71(3-4):73-77. doi:10.1515/ZNC-2016-0003
Cravotto C, Fabiano-Tixier AS, Claux O, et al. Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets. Foods. 2022;11(21). doi:10.3390/FOODS11213412
Zhang Z, Wang Y, Yang X, et al. Human Milk Lipid Profiles around the World: A Systematic Review and Meta-Analysis. Adv Nutr. 2022;13(6):2519-2536. doi:10.1093/ADVANCES/NMAC097
Manios Y, Karaglani E, Thijs-Verhoeven I, et al. Effect of milk fat-based infant formulae on stool fatty acid soaps and calcium excretion in healthy term infants: two double-blind randomised cross-over trials. BMC Nutr. 2020;6(1). doi:10.1186/S40795-020-00365-4
Zhang Z, Wang Y, Li Y, et al. Effects of Sn-2-palmitate-enriched formula feeding on infants’ growth, stool characteristics, stool fatty acid soap contents and bone mineral content: A systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2023;63(30):10256-10266. doi:10.1080/10408398.2022.2079606
Kennedy K, Fewtrell MS, Morley R, et al. Double-blind, randomized trial of a synthetic triacylglycerol in formula-fed term infants: effects on stool biochemistry, stool characteristics, and bone mineralization. Am J Clin Nutr. 1999;70(5):920-927. doi:10.1093/AJCN/70.5.920
Bar-Yoseph F, Lifshitz Y, Cohen T, Malard P, Xu C. SN2-Palmitate Reduces Fatty Acid Excretion in Chinese Formula-fed Infants. J Pediatr Gastroenterol Nutr. 2016;62(2):341-347. doi:10.1097/MPG.0000000000000971
Petit V, Sandoz L, Garcia-Rodenas CL. Importance of the regiospecific distribution of long-chain saturated fatty acids on gut comfort, fat and calcium absorption in infants. Prostaglandins Leukot Essent Fatty Acids. 2017;121:40-51. doi:10.1016/J.PLEFA.2017.05.007
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