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Comparative evaluation of the impact of acute exercise performed in the morning and evening on serum fatty acid profiles in trained and untrained men

Şermin Algül, Fatma Caf, Ayşe Şeker, Oğuz Özçelik · Human Movement · 2026

This study compared how a 45-minute aerobic workout performed in the morning versus evening affected blood fatty acid levels in 10 trained and 10 untrained men. Evening exercise increased certain fatty acids (stearic and linoleic acid) only in untrained participants, while trained individuals showed lower baseline fatty acid levels overall.
Takeaway: If you're untrained, prioritize morning exercise over evening workouts for potentially more favorable acute fatty acid responses.
Abstract (source)

Purpose: Exercise modulates lipid metabolism; however, the influence of the time of day on serum fatty acid responses remains incompletely understood. Although the effects of exercise intensity and duration are well documented, limited research has examined whether morning versus evening exercise produces different metabolic outcomes in individuals with varying training backgrounds. This study investigated the acute effects of morning compared with evening aerobic exercise on serum fatty acid profiles, including palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA), in trained and untrained men.

Methods: Twenty healthy men (n = 10 trained, n = 10 untrained) completed randomised morning (08:00–09:00) and evening (20:00 – 21:00) running sessions lasting approximately 45 minutes at 64–76% of their maximal heart rate (HRmax). Venous blood samples were collected before and after each session, and serum fatty acids were quantified using gas chromatography. A repeated-measures analysis of variance (ANOVA) was used to assess the effects of training status, exercise timing, and acute aerobic exercise.

Results: Levels of most serum fatty acids did not change significantly following exercise. However, in the untrained participants, evening exercise resulted in significant increases in C18:0 and C18:2 serum levels. Trained individuals demonstrated lower baseline C18:0 levels and lower evening SFA levels compared with the untrained participants. No significant differences were observed for C16:0, C18:1, MUFA, or PUFA levels.

Conclusions: The study

Findings: suggest that exercise timing influences serum fatty acid responses, particularly in untrained individuals. Evening exercise increased levels of lipogenesis-related fatty acids, and trained individuals exhibited a more favourable basal lipid profile. Considering exercise timing may help optimise lipid regulation and reduce cardiometabolic risk.

Randomized controlled trialOpen accessEndurance & CardiovascularRecovery & Sleep
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