Background: The objective of this systematic review is to analyze the influence of carbohydrate (CHO) intake on physical and technical aspects, glucose and muscle glycogen levels, fatigue, cognition, and gastrointestinal comfort involved in the performance of soccer players, as well as to examine whether there are any differences between men and women. Methods: A bibliographic search was conducted in PubMed, Web of Science, Scopus, and SportDiscus, resulting in 61 selected articles. The PRISMA recommendations and the Cochrane Handbook for Systematic Reviews guidelines were followed. Results: The results indicate that CHO intake before and during the match improves speed and the number of sprints, attenuates the decrease in shooting accuracy and speed, increases time to fatigue, and enhances cognitive function. There is no consensus on passing, dribbling, jumping, or agility improvements. Glucose levels drop during the first 15 min of the second half without affecting performance. Conclusions: It is recommended that players ingest 6–8 g/kg/d of CHO the day before, a meal with 1–3 g/kg 3–4 h before, and 30–60 g/h during the match. Muscle glycogen drops drastically at the end of the match, remaining low at 48 h. Hence, 1–1.5 g/kg/h is recommended during the first 4 h, starting from the first 20 min. Female soccer players have a similar physical demand to men, and energy availability is low, especially in the post-match periods, as they underestimate their energy expenditure and do not consume enough CHO. Therefore, the recommended guidelines should be followed, individualized, and periodized according to each athlete’s energy needs.

Collagen supplementation (CS) has emerged as a promising therapeutic approach with potential benefits for managing metabolic syndrome (MetS)-related risk factors. This narrative review integrates human evidence with preclinical mechanistic insights into the metabolic actions of collagen. Anti-obesity effects are attributed to increased satiety, gastric distension, GLP-1 secretion and enhanced fatty acid oxidation mediated by PPAR-α activation and AMPK signalling. In type 2 diabetes, collagen improves glucose homeostasis by enhancing insulin sensitivity, upregulating GLUT-4 and inhibiting dipeptidyl peptidase IV (DPP-IV), thereby prolonging incretin activity (GLP-1 and GIP) and supporting β-cell function. The antihypertensive effect of collagen peptides (CP) is primarily linked to angiotensin-converting enzyme (ACE) inhibition, which reduces angiotensin II levels while promoting bradykinin-mediated vasodilation and nitric oxide release. In addition, CP has shown potential in improving lipid profiles by modulating PPAR-γ and AMPK, increasing HDL-C and reducing LDL-C and triacylglycerols. Emerging evidence also supports a role for collagen in restoring gut microbiota balance, increasing short-chain fatty acid production and reducing pro-inflammatory and oxidative pathways, contributing to systemic metabolic regulation. Overall, these findings suggest CS exerts multi-targeted benefits on MetS components through modulation of endocrine, inflammatory and metabolic pathways. Nevertheless, larger, long-term clinical trials are warranted to determine optimal dosing regimens, evaluate long-term efficacy, and further elucidate microbiota-mediated effects.