Metabolic Effects of Linoleic Acid-Rich Oil Compared to a Blend Oil in Adults With Insulin Resistance

Official title

Role of Linoleic Acid in Cardiometabolic Health Beyond Its Lipid-lowering Effects, and Its Dietary and Pathophysiological Implications

Overview

Linoleic acid (LA), the predominant omega-6 polyunsaturated fatty acid in human diets, has been associated with improved lipid metabolism and insulin sensitivity compared with saturated fats. However, its role in metabolic health remains debated due to the limited number of well-controlled intervention studies. This randomized controlled trial aims to evaluate the metabolic effects of an LA-rich oil compared with a blended oil in adults with insulin resistance. Participants will be randomly assigned to receive either a daily supplement of LA-rich oil or a control blend oil for 8 weeks, while maintaining their usual diet and lifestyle. The primary outcome is the change in insulin resistance, assessed by the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR). Secondary outcomes include changes in fasting glucose, insulin, lipid profile, inflammatory and oxidative stress markers, and body composition. The study is designed as a single-blind, parallel-group intervention conducted at the Pontifical Catholic University of Chile. The results are expected to clarify the effects of increased dietary linoleic acid intake on insulin sensitivity and metabolic risk factors, contributing to the ongoing debate about the role of omega-6 fatty acids in cardiometabolic health.

Detailed description

Background

Non-communicable diseases (NCDs) are among the leading causes of morbidity and mortality worldwide. A healthy diet may help reduce the risk of these conditions by modulating the availability of nutrients and metabolites. However, the underlying mechanisms are not fully understood and may even lead to misconceptions.

A common example is the widespread belief that a high intake of omega-6 polyunsaturated fatty acids (PUFAs) is harmful to health. Without strong scientific support, some have advocated limiting dietary linoleic acid (LA)-the predominant PUFA in human diets-under the assumption that it competes biochemically with omega-3 fatty acids, thereby reducing their beneficial effects. Nevertheless, meta-analyses of prospective cohort studies have shown that higher LA intake or circulating levels are associated with lower total and LDL cholesterol, reduced cardiovascular disease risk, and a lower incidence of type 2 diabetes. These findings highlight the need to reassess the biological effects of LA and its potential role in metabolic regulation. To support evidence-based dietary recommendations promoting LA intake, well-controlled intervention studies are needed to better understand its cardiometabolic effects.

Hypothesis

Elevated blood levels of linoleic acid (LA), in response to increased dietary intake, confer cardiometabolic benefits beyond lipid-lowering effects, improving insulin sensitivity and reducing cardiovascular risk in individuals with cardiometabolic risk conditions.

Objectives

The primary objective is to evaluate the effect of a short-term intervention with an LA-enriched oil on insulin sensitivity and glucose homeostasis in adults with insulin resistance.

Secondary objectives include assessing the impact of the intervention on lipid profile, circulating fatty acid composition, inflammatory status, hepatic enzymes, oxidative stress markers, and estimated cardiovascular risk in Chilean adults with insulin resistance and cardiometabolic risk conditions.

Experimental Design

This study is a randomized, single-blind, controlled, parallel-group clinical trial conducted at the Clinical Research Center (CICUC) of the Pontifical Catholic University of Chile. Eligible adults with insulin resistance will be randomly assigned in a 1:1 ratio to receive either a linoleic acid-rich oil or a blend oil for 8 weeks at a dose of 0.4 mL per kilogram of body weight per day. Fasting blood samples will be collected at baseline and at 8 weeks to assess insulin resistance (HOMA-IR), lipid profile, circulating fatty acid composition, inflammatory and oxidative stress markers (AOPP, oxidized LDL), and hepatic enzymes. Anthropometric and clinical parameters will also be recorded following standardized protocols.

Interventions

• Dietary supplement Linoleic Acid-Rich Oil
  Participants in the experimental group will receive a daily supplement of a linoleic acid (LA)-rich oil at a dose of 0.4 mL per kilogram of body weight per day, taken orally for 8 weeks. The oil is characterized by a high content of omega-6 polyunsaturated fatty acids, primarily linoleic acid (\~60%). To facilitate adherence and appropriate use, participants will receive a recipe booklet encouraging the use of the oil in cold or minimally cooked preparations, or as a topping over foods. They wi
• Dietary supplement Blend Oil
  Participants in the control group will receive a daily supplement of a blend oil at a dose of 0.4 mL per kilogram of body weight per day, taken orally for 8 weeks. The blend was formulated to contain approximately equal proportions of saturated, monounsaturated, and polyunsaturated fatty acids, with less than half the linoleic acid content of the LA-rich oil. Participants will receive a recipe booklet promoting the use of the oil in cold dishes or lightly cooked preparations, or as a dressing o

Primary outcome measures

• Change in insulin resistance (HOMA-IR) [Time frame: Baseline and 8 weeks after the start of the intervention.]

Secondary outcome measures (12)

• Glycated hemoglobin (HbA1c) [Time frame: Baseline and week 8]
• Fasting glucose [Time frame: Baseline and week 8]
• Fasting insulin [Time frame: Baseline and week 8]
• Lipid profile [Time frame: Baseline and week 8]
• Liver enzymes [Time frame: Baseline and week 8]
• Body Weight [Time frame: Baseline and week 8]
• Body mass index (BMI) [Time frame: Baseline and week 8]
• Waist circumference [Time frame: Baseline and week 8]
• Inflammatory markers [Time frame: Baseline and week 8]
• Oxidative stress markers [Time frame: Baseline and week 8]
• Change in plasma fatty acid profile [Time frame: Baseline and week 8]
• 24-hour dietary recall [Time frame: Baseline and week 8]

Eligibility criteria

Inclusion criteria

• Men and women aged 20 to 60 years.
• Insulin resistance (HOMA-IR > 2.6).
• At least one cardiometabolic risk factor: abdominal obesity (waist circumference > 90 cm in men or > 80 cm in women); low HDL-cholesterol (< 40 mg/dL in men or < 50 mg/dL in women); elevated LDL-cholesterol (> 70 / 100 / 130 mg/dL, according to estimated cardiovascular risk); or elevated blood pressure (≥ 130/85 mmHg).

Exclusion criteria

• Diabetes diagnosis.
• Severe psychiatric illness.
• Malabsorption disorders or previous bariatric surgery.
• Pregnancy or lactation.
• Previous clinical cardiovascular disease.
• Regular use of medications that could influence study outcomes, including:

lipid-lowering agents insulin sensitizers antihypertensive drugs anticoagulants antiretroviral therapy thyroid hormones oral corticosteroids immunosuppressants polyunsaturated fatty acid (PUFA) supplements.

• Fasting serum triglycerides ≥ 500 mg/dL or LDL-cholesterol ≥ 190 mg/dL.
• Body mass index (BMI) ≥ 35 kg/m².
• Very high blood pressure.
• Any additional condition that may limit adherence to the study.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Treatment

Study locations

Chile · 1 center

• Centro de Investigaciones Clínicas UC (CICUC) - Pontificia Universidad Católica de Chile — Santiago

Publications

• Berkowitz L, Echeverria G, Salazar C, Faundez C, Coe CL, Ryff C, Rigotti A. Lipidomic Signature of Healthy Diet Adherence and Its Association with Cardiometabolic Risk in American Adults. Nutrients. 2024 Nov 22;16(23):3995. doi: 10.3390/nu16233995. PMID 39683389
• Berkowitz L, Razquin C, Salazar C, Biancardi F, Estruch R, Ros E, Fito M, Corella D, Coe CL, Ryff CD, Ruiz-Canela M, Salas-Salvado J, Wang D, Hu FB, Deik A, Martinez-Gonzalez MA, Rigotti A. Sphingolipid profiling as a biomarker of type 2 diabetes risk: evidence from the MIDUS and PREDIMED studies. Cardiovasc Diabetol. 2024 Dec 18;23(1):446. doi: 10.1186/s12933-024-02505-7. PMID 39695759
• Berkowitz L, Mateo C, Salazar C, Samith B, Sara D, Pinto V, Martinez X, Calzada M, von Schultzendorff A, Pedrals N, Bitran M, Echeverria G, Ruini C, Ryff C, Rigotti A. Healthy Eating as Potential Mediator of Inverse Association between Purpose in Life and Waist Circumference: Emerging Evidence from US and Chilean Cohorts. Int J Environ Res Public Health. 2023 Nov 23;20(23):7099. doi: 10.3390/ijerp PMID 38063529
• Calderon M, Plaza G, Gomez M, Samith B, Pinto V, Martinez X, Sara D, Echeverria G, Calzada M, Berkowitz L, von Schultzendorff A, Pedrals N, Bitran M, Rigotti AG. [Limitations and opportunities for the appropriation of the Mediterranean diet in Chilean adults with diagnostic elements of metabolic syndrome]. Nutr Hosp. 2024 Feb 15;41(1):86-95. doi: 10.20960/nh.04652. Spanish. PMID 38047416
• Echeverria G, Samith B, von Schultzendorf A, Pinto V, Martinez X, Sara D, Calzada M, Pacheco J, Plaza G, Scott F, Romero J, Mateo C, Julio MV, Utreras-Mendoza Y, Binder MV, Gutierrez F, Riquelme ME, Cuevas M, Willatt R, Sanchez O, Keilendt A, Butron P, Jarufe A, Huete I, Tobar J, Martin S, Alfaro V, Olivos M, Pedrals N, Bitran M, Avalos I, Ruini C, Ryff C, Perez D, Berkowitz L, Rigotti A. Mediterr PMID 37538196

Identifiers

NCT: NCT07287514 · 230330018 · 11240454

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗