Obesity is prevalent amongst individuals with achondroplasia (the most common form of disproportionate short stature), yet few studies exist on the metabolic health profile of these individuals, and none have examined post-prandial responses. Therefore, this study characterised the post-prandial responses of systemic metabolites and metabolic substrate oxidation rates of 40 individuals with various forms of extreme morphology (ACHON, individuals with achondroplasia, n = 22; OTHER SD, individuals with a diagnosed form of skeletal dysplasia other than achondroplasia, n = 4; SMALL, individuals with no diagnosed form of restricted growth but matched for fat-free mass (<47.5 kg), n = 4; and LARGE, individuals with high fat-free mass (>57.25 kg for females and 75.35 kg for males, as comparators), n = 10). Participants visited the laboratory for an oral glucose tolerance test (OGTT; 75 g glucose, including 150 mg of [U-¹³C] glucose), followed 3 hours later by a mixed-meal tolerance test (MMTT; 100 g carbohydrate, 50 g fat and 30 g protein). Arterialised blood samples were collected throughout the post-prandial periods, with expired breath samples analysed to calculate substrate oxidation via indirect calorimetry and exogenous carbohydrate oxidation via EA-IRMS (elemental analyser – isotope ratio mass spectrometry; Sercon Hydra 20-20 IRMS). Across the 180-minute OGTT, the ACHON group oxidised the highest absolute quantity of the ingested carbohydrate (mean 24.0 g; 95 % CI 22.0, 26.0 g), relative to the OTHER SD, SMALL and LARGE groups. Individuals in the ACHON group also oxidised more carbohydrate across the MMTT (52.0 ± 31.1 g·180 min^-1; mean ± standard deviation); over 4-fold greater than that measured in the SMALL group (11.9 ± 10.6 g·180 min^-1, p < 0.001), and almost 3-times greater than that measured in the OTHER SD group (17.8 ± 11.2 g·180 min^-1, p < 0.001), but a similar quantity to the LARGE group (50.0 ± 30.6 g·180 min^-1, p = 0.867). Plasma glucose incremental area under the curve (iAUC) for the OGTT was higher in the ACHON group (545 ± 166 mmol·L^-1·180 min), compared to individuals with SMALL (428 ± 219 mmol·L^-1·180 min) and LARGE body size (368 ± 253 mmol·L^-1·180 min). At 120 minutes into the OGTT, plasma glucose concentrations were on average highest in the ACHON group (8.4 ± 1.5 mmol·L^-1), compared to the OTHER SD (7.6 ± 1.4 mmol·L^-1), SMALL (6.0 ± 1.7 mmol·L^-1) and LARGE groups (7.5 ± 3.5 mmol·L^-1). In summary, individuals with achondroplasia appear to prioritise exogenous carbohydrate oxidation when ingesting a glucose bolus and mixed-macronutrient meal, compared to those with other forms of skeletal dysplasia and varied/extreme body sizes and proportions. In contrast to previous reports of normoglycaemia within achondroplasia, the current cohort of individuals with achondroplasia displayed dysregulated glycaemic control on average, with 16 individuals in the prediabetic/diabetic range.