As hospitals move beyond traditional soybean oil-based nutrition, researchers are probing whether olive or fish oil formulations offer meaningful advantages for patients who depend on intravenous feeding.

Study: Comparison of Olive Versus Fish Oil Based Parenteral Nutrition and Clinical Outcomes - A Systematic Review. Image Credit: Nicoleta Ionescu / Shutterstock

A recent systematic review published in the Journal of Human Nutrition and Dietetics found that direct evidence comparing olive- and fish-oil-containing parenteral nutrition (PN) formulations remains limited, with no clear evidence that either is superior for hospitalized adults.

Previous evidence suggests that reducing soybean oil content in PN may provide clinical benefits, while olive- and fish-oil-containing formulations have been proposed to influence immune, inflammatory, and liver-related outcomes. However, in the six trials reviewed, the two approaches did not differ significantly in major clinical outcomes such as hospital length of stay. More research is needed to determine whether olive or fish oil formulations provide greater clinical benefits and to guide their use in hospitalized adults.

PN has become an essential support for patients who may not be able to meet their regular nutritional requirements via oral or enteral routes. Researchers are trying to identify which lipid emulsion would confer the greatest clinical benefit to such individuals. Research efforts are ongoing to compare emulsions based on fish oil and olive oil in acute care settings.

Existing literature provides inconsistent findings. Some studies suggest that fish oil-containing PN can lower infection risk after surgical procedures, while other studies report less pronounced clinical benefits and suggest that fish oil-containing formulations may not provide sufficient essential fatty acids for long-term use. Other studies have reported reductions in total bilirubin concentrations over time with both fish- and olive-oil-containing PN.

About the review

In the present systematic review, researchers compared third-generation olive oil and fourth-generation fish oil-containing PN formulations and evaluated clinical outcomes.

The team searched the Embase, Medline, Web of Science, and CINAHL databases for intervention studies and randomized controlled trials (RCTs) comparing olive oil and fish oil-based PN for inpatients aged at least 18 years. Non-experimental observational studies, systematic reviews, and meta-analyses were excluded, as were studies involving animal models, pediatric populations, or patients receiving PN at home.

Once relevant records were obtained, two independent researchers screened the titles and abstracts. Full-text screening was subsequently performed. They evaluated the risk of bias in the included studies using the Cochrane risk-of-bias tool, version 2 (RoB 2). During the data extraction process, the researchers recorded study characteristics, participant characteristics, intervention and control groups, and study outcomes. For each included study, the team documented authors, country, publication year, study design, study duration, participant age, diagnosis, and PN regimen, including indication, composition, and duration.

Results and discussion

The initial search yielded 3,424 papers. After removing 739 duplicates, 2,569 papers that did not fulfill the selection criteria, 109 papers with ineligible study designs, and one paper with inaccessible full text, the team reviewed six RCTs. In the included trials, the primary outcomes were related to oxidative stress, inflammation, and infection in studies conducted in Spain, Mexico, and Turkey.

The trials comprised postoperative patients, type 2 diabetes patients, and people diagnosed with septic shock or intestinal failure. The mean age of the participants ranged between 45.5 and 72.1 years. In all trials, PN was provided to participants for at least four days. The risk of bias was low in three studies, high in two, and raised some concerns in one. The small number of studies and wide variation in reported outcomes prevented the researchers from conducting a meta-analysis.

Importantly, the fish oil interventions were not uniform. All six studies used fish oil alongside other lipid emulsions, either in mixed formulations or by adding fish oil to olive oil-based PN. Differences in formulation and fish oil concentration meant that the researchers could not establish exact dosing or compare doses across studies.

In one low-risk trial, infections during the first seven days of PN were significantly more frequent among fish-oil recipients, although overall infection rates did not differ significantly between groups (54% with olive oil vs. 47% with fish oil). Another trial found a significant difference in non-septic infections, with higher incidence rates among olive oil recipients compared to those receiving fish oil for five or more days (approximately 79% vs. 23%). Sepsis was also numerically less frequent in the fish oil group in this trial, but the difference was not statistically significant.

Individual trials reported significantly lower glucose, bilirubin, interleukin-8 (IL-8), and IL-17A levels, and higher high-density lipoprotein (HDL) levels with fish-oil-containing PN. The IL-8 and IL-17A findings, however, came from a study judged to have a high overall risk of bias. These findings arose from different studies and were not consistently demonstrated across the evidence base. In one study, thiobarbituric acid reactive substance (TBAR) levels were significantly lower following olive oil-containing PN use.

In the olive oil group, mean C-reactive protein (CRP) levels tended to be higher, while another study showed non-significant trends toward a lower rise in both interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) compared with the fish oil group. However, these findings did not attain statistical significance. The included studies reported differing trends regarding prealbumin levels in the study groups, but none found a significant between-group difference.

Olive oil is primarily composed of oleic acid, along with bioactive components such as phytosterols, alpha-tocopherol, and phenolic compounds, which possess antioxidant and potentially anti-inflammatory properties. Fish oil is rich in long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which serve as precursors to various anti-inflammatory modulators. These differences in fatty acid composition may partly explain the proposed benefits of newer lipid emulsions compared with soybean oil-based formulations.

Conclusion

Previous evidence suggests that reducing soybean oil content in PN can provide clinical benefits, but the six directly comparative trials included in this review did not establish that fish-oil-containing PN was superior to olive oil-based PN, or vice versa. It remains unclear whether either olive- or fish-oil-containing PN is superior to the other in influencing immune function, liver function, clinical outcomes, or inflammation for hospitalized adults. In future studies, researchers should include more high-quality RCTs with clearly defined and comparable lipid formulations and dosing regimens to confirm the findings and determine the benefits of later-generation lipid emulsions in patient subgroups.

Journal reference:

• Carey, S., Astorga, M., Hubble, A., and Ferrie, S. (2026). Comparison of Olive Versus Fish Oil Based Parenteral Nutrition and Clinical Outcomes-A Systematic Review, Journal of Human Nutrition and Dietetics, 39, e70331, DOI: 10.1111/jhn.70331, https://onlinelibrary.wiley.com/doi/10.1111/jhn.70331