Tipping the balance: why ARA:DHA ratio and level matter in infant formula

• Earlier this year, infant formula recalls due to arachidonic acid (ARA) contamination put the quality of nutritional lipids under the microscope—raising broader questions about the importance and safety of ARA in early life nutrition.
• However, the concerns about product quality should not overshadow decades of scientific evidence supporting ARA's nutritional importance—together with docosahexaenoic acid (DHA).
• Read on to explore the science behind ARA in infant formulas and learn why providing ARA and DHA at appropriate levels and ratios matters for infant development.

Breast milk is the gold standard for infant nutrition and the primary reference point for infant formula composition. An extensive body of literature shows that breast milk always contains ARA and DHA. Notably, ARA levels consistently exceed those of DHA in human milk, with evidence showing average ARA concentrations of 0.47—0.55% of total fatty acids versus 0.32–0.37% for DHA.^1,2 This yields an ARA:DHA ratio of approximately 1.5:1. 

These findings point to two important considerations for infant formula: providing sufficient amounts of both ARA and DHA, and achieving an appropriate balance between them. The ratio alone does not tell the whole story—the absolute levels of each fatty acid matter too. This matters because, while infants can synthesize ARA and DHA, the conversion rate is too low to meet their demands during this period of rapid growth and development, meaning they depend on dietary supply. If breastfeeding is not possible and infant formula is required, it is important that formula mimics breast milk closely by providing ARA and DHA at the appropriate levels and ratios. Indeed, infants fed formula without ARA can show up to 50% reductions in ARA status compared to breastfed peers.^3,4,5,6,7 This highlights the importance of including ARA in infant formula to help ensure formula-fed babies do not miss out on this fatty acid, which is so important for healthy growth and development.

ARA benefits: neurodevelopment and beyond

ARA and DHA are well known for their roles in neurodevelopment, including visual and cognitive development, with the latter encompassing attention, memory, language, intelligence, learning, and problem solving. Both fatty acids accumulate rapidly in the brain and other neurological tissues from the third trimester of pregnancy and then for the first couple of years postpartum and beyond.  Consistent with these findings, clinical studies in infants receiving formula supplemented with ARA and DHA have shown that this nutritional lipid combination can lead to important neurodevelopmental and cognitive outcomes from infancy up to at least nine years of age.^{9,10,11,12,13}

The physiological impacts of ARA extend well beyond the brain too. It is the major unsaturated fatty acid in the heart, muscles, liver, kidneys, and key immune cells. It is also a precursor for eicosanoids—signaling molecules involved in inflammation, immune response, blood clotting, and vascular development.^1,5,14 Interestingly, ARA in breast milk is also associated with reduced asthma risk, especially in infants with genetically low ARA synthesis.¹⁵

Getting ARA and DHA right: why levels and ratios matter 

One of the most exciting bodies of research in this space is the DIAMOND trial—a landmark study that investigated both short- and long-term neurodevelopmental outcomes in formula-fed infants.¹⁶ The study compared a control formula containing no ARA or DHA against three test formulas providing different levels of DHA (0.32%, 0.64%, and 0.96% of fatty acids), all within the global human milk range, with ARA held constant at 0.64% of fatty acids. This allowed researchers to investigate not only the effects of ARA and DHA supplementation, but also how different DHA levels—and the resulting ARA:DHA ratios of 2:1, 1:1, and 1:1.5— influenced a range of cognitive, behavioral, and brain outcomes from 1.5 months through nine years of age.

The results were striking. Compared to the control formula which contained no ARA or DHA, infants fed the supplemented formulas showed statistically significant improvements across a wide range of neurodevelopmental measures. These included sustained attention at four, six, and nine months; visual acuity at 12 months; and mental development scores at 18 months. Benefits also extended to executive function (specifically rule-learning and implementation) from three to five years; language and vocabulary at five years; and verbal and full-scale IQ at six years.^{9,10,12,17,18,19}

Another important finding from the DIAMOND study was that cognitive benefits were consistently present when ARA equaled or exceeded DHA—and often diminished when DHA exceeded ARA. At the 1:1.5 ratio (where ARA levels were lower than DHA), sustained attention, mental adaptability, verbal IQ, and composite intelligence scores were reduced compared to the two groups where ARA was equal to or higher than DHA. When the DHA content exceeded ARA, the ARA status in red blood cells also decreased dramatically even though the formula level of ARA remained the same. A likely mechanism could be that ARA and DHA compete for the same mechanisms to be incorporated into red blood cells and brain tissues. As such, the potential consequences of providing more DHA than ARA in formula could lead to reduced ARA status and a loss of certain neurodevelopmental benefits.

Closing the regulatory gap with science-backed recommendations

The scientific consensus is clear. With the exception of the European Commission, all national and international regulations and standards require that ARA must be added to infant formula when DHA is included—at least to the same level. A group of 25 international experts agreed, concluding that DHA without balanced ARA may reduce brain ARA concentrations, impair neurodevelopment, and adversely affect growth and immune function.¹² Critically, formulas providing DHA—but without ARA—have not been adequately evaluated for safety in healthy term infants.

Jim Richards, Head of Nutrition, Science and Advocacy from dsm-firmenich remarks: “It is our position that all formulas intended for infants should include DHA from 20–50 mg/100kcal, and that ARA should be added to at least the same level as DHA, with an ARA:DHA ratio of 1:1 – 2:1, and a maximum inclusion of 50 mg/100 kcal.”