Introduction: Long-term fasting (LF) activates an adaptative response to switch metabolic fuels from food glucose to lipids stored in adipose tissues. The increase in free fatty acid (FFA) oxidation during fasting triggers health benefits. We questioned if the changes in lipid metabolism during LF could affect lipids in cell membranes in humans. We thus analysed the FA composition in erythrocyte membranes (EM) during 12.6 ± 3.5 days of LF and 1 month after food reintroduction.
Methods: A total of 98 subjects out of three single-arm interventional studies underwent a medical supervised long-term fasting (12.6 ± 3.5 days) programme. The distribution pattern of 26 FA as well as the HS-Omega-3 Index were assessed in the EM using gas chromatography.
Results: Eighteen of 26 FA showed significant changes. Within the group of saturated FA, myristic (14:0) and stearic acid (18:0) decreased while palmitic (16:0) and arachid acid (20:0) increased. While most monounsaturated FA increased, trans fatty acids decreased or remained unchanged. Within the polyunsaturated FA, arachidonic (20:4n6) and docosahexaenoic (22:6n3) acid increased, while linoleic (18:2n6), alpha-linolenic (18:3n3) and eicosapentaenoic acid (20:5n3) decreased. Consequently, the HS-Omega-3 Index increased. 11 out of the 18 FA with significant changes returned to baseline levels 1 month afterwards. Levels of linoleic and alpha-linolenic acid increased over baseline levels.
Conclusions: Long-term fasting triggers changes in the FA composition of EM.
Keywords: Omega‐3 index; adipose tissue; erythrocyte; fasting; fatty acids; long‐term fasting.
© 2025 The Author(s). European Journal of Clinical Investigation published by John Wiley & Sons Ltd on behalf of Stichting European Society for Clinical Investigation Journal Foundation.