Background/Objectives: Ultra-processed foods (UPFs) have become a dominant component of the modern diet, paralleling the rise in obesity and chronic disease prevalence worldwide. This narrative review aims to synthesize evidence on how dietary processing and UPF consumption interacts with dietary quality, energy balance, and biological pathways to influence metabolic health. Methods: We performed a targeted literature search of peer-reviewed articles and authoritative reports examining UPF definition (via the NOVA classification), global consumption patterns, behavioral drivers of overconsumption, nutrient composition, and mechanistic links to metabolic dysfunction. Emphasis was placed on recent human and animal research relating UPFs to obesity, cardiometabolic outcomes, inflammation and gut microbiome alterations. Results: High UPF intake is consistently associated with reduced diet quality (higher saturated fat, sugar, sodium; lower fiber and micronutrients), increased energy density, faster eating rates and activation of reward pathways. These factors facilitate excessive energy intake and adiposity, promoting metabolic dysregulation, chronic low-grade inflammation, hormonal disturbances and gut microbiome shifts. While cross-sectional and cohort evidence is extensive, causal intervention trials and mechanistic human work remain limited. Conclusions: The accumulated evidence suggests that UPFs may influence chronic disease risk through their unbalanced nutrient profiles and through additional effects introduced by industrial processing. To translate these insights into public health strategies, future work should prioritize real-world intervention studies to reduce UPF consumption and examine resulting effects on energy balance, inflammation and gut health.

Normal weight obesity (NWO) is a body composition phenotype that is associated with increased cardiometabolic risk and is characterized by a normal weight body mass index but elevated body fat. The purpose of this study was to determine sex differences in aerobic capacity across body composition phenotypes, including normal weight lean (NWL), NWO, and traditional obesity (OB). We recruited 60 participants according to three body composition phenotypes: NWL (n = 10 females, n = 10 males), NWO (n = 10 females, n = 10 males), and OB (n = 10 females, n = 10 males). Measurements included fasting metabolic risk factors, body composition X-ray scan, and peak exercise test on a cycle ergometer to determine aerobic capacity (VO_2peak). Across groups, males (34.5 ± 11.7 mL/kg/min) exhibited greater VO_2peak than females (28.8 ± 8.8 mL/kg/min; p = 0.04). There were no differences in VO_2peak between sexes within the same body composition phenotype, but NWL (42.7 ± 9.0 mL/kg/min) exhibited greater VO_2peak than NWO (27.9 ± 4.4 mL/kg/min; p < 0.0001) and OB (24.4 ± 7.3 mL/kg/min; p < 0.0001). VO_2peak was inversely correlated with relative body fat in the full sample (r = −0.67; p < 0.0001), but was stronger in males (r = −0.78; p < 0.0001) than females (r = −0.53; p = 0.0028). Visceral adipose tissue was not significantly correlated with VO_2peak in the full sample (r = −0.25; p = 0.05) or in males (r = −0.23; p = 0.25), although they were inversely correlated in females (r = −0.36; p = 0.048). Our results suggest low aerobic capacity in both men and women with NWO, similar to men and women with OB. The relationship between body composition and aerobic capacity is strong across body composition phenotypes, but appears to be more consistent in females than males. For healthcare professionals aiming to lower cardiometabolic risk, attention should be given to improving aerobic fitness in both men and women with elevated body fat, including those with NWO.