Background <p>Diet and lifestyle are key modifiable risk factors for the components of metabolic syndrome (MetS). In low- and middle-income countries undergoing nutrition transition, the relative importance of dietary patterns versus broader lifestyle, socio-demographic, and economic determinants of metabolic risk remains unclear, particularly among young adults. This study aimed to examine these associations in Rwanda.</p> Methods <p>Between January and April 2023, a community-based cross-sectional survey was conducted among Rwandan adults aged 18–35 years (<i>N</i> = 699). Dietary intake was assessed with a validated food frequency questionnaire, and dietary patterns were derived using exploratory factor analysis. Lifestyle behaviour patterns were identified using latent class analysis based on seven risk behaviours. Metabolic risk factors were assessed following WHO STEP-wise approach. A Mixed-effect logistic regression, with province included as a random effect, examined associations between dietary/lifestyle patterns and MetS components, adjusting for socio-demographic and economic factors.</p> Results <p>Three dietary patterns were identified (<i>Modern</i>, <i>Low-variety</i>, and <i>Traditional)</i>. Latent class analysis yielded two lifestyle classes: a lower-risk unhealthy lifestyle class (25.75%) and a higher-risk unhealthy lifestyle class (74.25%) characterized by greater probability of smoking, heavy episodic drinking, sedentary behaviour, inadequate sleep, and high salt intake. Individual metabolic risk factors were common (e.g., reduced high-density lipoprotein-cholesterol HDL-C: 25.9%; abdominal obesity: 20.3%), though MetS prevalence was low (5.4%). In multivariable-adjusted analyses, dietary patterns showed no independent associations with any MetS component. In contrast, the high-risk lifestyle pattern was positively associated with elevated fasting blood glucose (Odd Ratio, OR = 2.05, 95% Confidence Interval, CI: 1.14, 3.70) and inversely associated with abdominal obesity (OR = 0.36, 95% CI: 0.20, 0.67). Socio-demographic and economic factors, particularly sex, age, occupation, and urban/rural residence, showed strong and consistent associations with MetS components.</p> Conclusion <p>Among young adults in Rwanda, lifestyle and socio-demographic and economic factors showed more consistent associations with metabolic risk indicators, whereas dietary patterns did not show independent associations. Future longitudinal investigations incorporating additional lifestyle factors and objective dietary assessment methods to overcome the inherent limitations of self-reported intake are warranted. In parallel, public health policy should prioritise targeted, community-based lifestyle interventions and socioeconomic disparity-reduction strategies to reduce metabolic risk among young adults.</p> Trial registration <p>The study was registered as a clinical trial on November 27, 2019, at clinicaltrials.gov (reference number NCT04204538).</p>