The influence of intermittent fasting on body metrics, lipid profile, and physical performance in young and middle-aged men

<b>Background:</b> Intermittent fasting (IF) is increasingly adopted for weight and metabolic health management, yet its impact on lipid profile and physical performance in young and middle-aged men remains unclear. <b>Aim:</b> The present study examined the effect of a five-month (IF) on body composition, lipid profile, and physical performance. <b>Methods:</b> A randomized controlled trial was conducted to evaluate the impact of this eating pattern. Forty active male participants were divided into two age groups (a young group from 23 to 28 years and a middle-aged group from 46 to 59 years) and then randomly assigned to experimental (young experimental group (YE), middle-aged experimental group (ME)) or control groups (young control group, middle-aged control group). Before and after the five-month (IF) intervention (4 days per week), all participants performed the Running-based Anaerobic Sprint and the Test Blood for the determination of lipids profile. <b>Results:</b> Both young (YE) and middle-aged (ME) experimental groups showed significant reductions in weight (<i>p</i> = 0.012 for YE and <i>p</i> = 0.011 for ME), body mass index (BMI) (<i>p</i> = 0.011 for YE and <i>p</i> = 0.012 for ME) and fat-free mass (<i>p</i> = 0.004 for YE and <i>p</i> = 0.043 for ME) compared to control groups. Analysis of variance (ANOVA) revealed significant main effects of time and group for weight (<i>p</i> < 0.001; <i>p</i> = 0.012), BMI (<i>p</i> = 0.012; <i>p</i> = 0.038), and fat-free mass (<i>p</i> = 0.023; <i>p</i> = 0.037), with significant time × group interaction for weight (<i>p</i> = 0.017) and trends for BMI (<i>p</i> = 0.048) and fat-free mass (<i>p</i> = 0.07); no significant effects were observed for body fat percentage (<i>p</i> > 0.05). In addition, our results showed that (IF) was associated with significant decrease in total cholesterol (<i>p</i> = 0.004 for YE and <i>p</i> = 0.0024 for ME) and high-density lipoprotein (HDL) levels (<i>p</i> = 0.004 for YE and <i>p</i> = 0.009 for ME) in both experimental groups. Low-density lipoprotein decreased significantly only in the young IF group (<i>p</i> = 0.041). However, IF did not affect triglyceride levels or physical performance. ANOVA revealed a significant interaction between time and group for HDL (<i>p</i> < 0.001), with greater reductions in middle-aged participants, and a significant group effect for triglycerides (<i>p</i> < 0.001), which were higher in middle-aged groups at both time points. <b>Conclusion:</b> These results suggest that while IF can positively influence body composition and is associated with selective changes in lipid profiles, its effects on triglycerides and physical performance may be limited. These findings underscore the need for further research to explore the long-term metabolic implications of IF, as well as potential age-related differences in response to fasting regimens.