Age-Related Variations in Body Composition and Metabolic Health: A Cross-Sectional Study in Adults

Background and Objectives: Midlife represents a critical window for the emergence of metabolic risk factors. This study aimed to investigate age- and sex-related changes in lipid profiles, body composition, oxidative stress, and fatty acid content. Materials and Methods: This cross-sectional study included adults grouped by age: <30, 30-39, and 40-49 years. The assessments covered body composition (fat mass, fat distribution, and lean mass), fasting lipids, inflammation markers measurements, and platelet fatty acids evaluation. Results: In total, 169 adults took part in this study (60 men and 109 women), aged 36.30 ± 6.25 years. Fat mass and its regional distribution were higher after age 40, especially in females. In women, fat mass was lower in the thirties and higher again in the forties, while, in men, fat accumulation was progressive. Participants aged 40-49 had a significantly worse metabolic profile than younger individuals. Statistically significant higher total cholesterol, LDL cholesterol, triglycerides, and glucose were shown in the 40-49-years group when compared to younger groups. Malondialdehyde was higher in the 40-49-years vs. 30-39-years group (105.83 vs. 99.72, p = 0.034). In women aged 40-49, a more adverse lipid and glycemic profile was observed compared to younger groups. Platelet fatty acids in the 40-49-years group showed higher polyunsaturated fatty acids and ω6 percentages (12.85% vs. 10.14%, p = 0.046 and 11.44% vs. 8.79%, p = 0.031), including higher linoleic (8.80 ± 5.18 vs. 6.97 ± 5.05, p = 0.045), arachidonic (2.64 ± 2.64 vs. 1.82 ± 1.73, p = 0.030), and docosahexaenoic (0.61 ± 0.86 vs. 0.31 ± 0.49, p = 0.008) acids, when compared to younger groups. Fat mass strongly correlated with insulin resistance, triglycerides, and CRP, and inversely with HDL-C. Conclusions: Significant age-related changes in body composition, metabolic biomarkers, and platelet fatty acid profiles occur after the age of 40, with distinct gender-specific patterns. The fifth decade of life is a transitional period characterized by central adiposity, deteriorating metabolic profiles, and altered fatty acid composition, especially in women.