Essential Fatty Acid Requirements and Intravenous Lipid Emulsions

Abstract

Linoleic acid (LA) and α‐linolenic acid (ALA) must be supplied to the human body and are therefore considered essential fatty acids. This narrative review discusses the signs, symptoms, diagnosis, prevention, and treatment of essential fatty acid deficiency (EFAD). EFAD may occur in patients with conditions that severely limit the intake, digestion, absorption, and/or metabolism of fat. EFAD may be prevented in patients requiring parenteral nutrition by inclusion of an intravenous lipid emulsion (ILE) as a source of LA and ALA. Early ILEs consisted solely of soybean oil (SO), a good source of LA and ALA, but being rich in LA may promote the production of proinflammatory fatty acids. Subsequent ILE formulations replaced part of the SO with other fat sources to decrease the amount of proinflammatory fatty acids. Although rare, EFAD is diagnosed by an elevated triene:tetraene (T:T) ratio, which reflects increased metabolism of oleic acid to Mead acid in the absence of adequate LA and ALA. Assays for measuring fatty acids have improved over the years, and therefore it is necessary to take into account the particular assay used and its reference range when determining if the T:T ratio indicates EFAD. In patients with a high degree of suspicion for EFAD, obtaining a fatty acid profile may provide additional useful information for making a diagnosis of EFAD. In patients receiving an ILE, the T:T ratio and fatty acid profile should be interpreted in light of the fatty acid composition of the ILE to ensure accurate diagnosis of EFAD.

Emergence of Mixed‐Oil Fat Emulsions for Use in Parenteral Nutrition

“…Although, ω‐3 and ω‐6 fatty acids are preferred by these enzymes, in the presence of deficiency, Mead acid levels can be elevated. In addition, this increased accumulation of Mead acid or eicosatrienoic acid (20:3ω‐9), compared with arachidonic or eicosatetraenoic acid (20:4 ω‐6), leads to an elevation in the triene/tetraene ratio, which is typically substantially <0.4 20 . With the use of IFE‐free PN, biochemical manifestations of EFAD (fall in linoleic acid [LA], triene/tetraene ratio >0.4, and elevated Mead acid level) can be noted 2–4 weeks after PN initiation 10 , 21 – 23 .…”

“…With the use of IFE‐free PN, biochemical manifestations of EFAD (fall in linoleic acid [LA], triene/tetraene ratio >0.4, and elevated Mead acid level) can be noted 2–4 weeks after PN initiation 10 , 21 – 23 . If not treated, clinical signs of hair loss, scaly skin, and abnormal liver function tests present several weeks later, followed by reduced growth, dermatitis, hair loss, and liver dysfunction 20 . Fortunately, SO contains 50% of fat as LA and 10% as α‐linolenic acid, requiring only a small amount of IFE to prevent EFAD (2.9–8.7 g/d or 29–87 mL Intralipid in a 60‐kg individual receiving 25 kcal/kg/d) 20 , 24 , 25 .…”

“…If not treated, clinical signs of hair loss, scaly skin, and abnormal liver function tests present several weeks later, followed by reduced growth, dermatitis, hair loss, and liver dysfunction 20 . Fortunately, SO contains 50% of fat as LA and 10% as α‐linolenic acid, requiring only a small amount of IFE to prevent EFAD (2.9–8.7 g/d or 29–87 mL Intralipid in a 60‐kg individual receiving 25 kcal/kg/d) 20 , 24 , 25 . The amount may vary based on age, ability to tolerate some oral intake, and initial nutrition status, with major organizations such as the European Society of Parenteral and Enteral Nutrition taking the conservative approach of recommending at least 1g/kg/wk of IFE to prevent EFAD in adults 2 …”

“…No significant difference was noted, however, in clinical outcomes 72 – 74 . In addition, given the reduction in LA with the substitution of SO for OO, concern was also raised regarding the development of EFAD 75 . Trial data demonstrated a significant reduction in α‐linolenic acid but also noted higher Mead acid levels.…”

“…Trial data demonstrated a significant reduction in α‐linolenic acid but also noted higher Mead acid levels. Since there was no clinical evidence for development of EFAD and triene/tetraene ratios remained normal, it was hypothesized that these changes were more likely due to the composition of ClinOleic 20% rather than the development of EFAD 75 …”