Introduction: The coronavirus disease 2019 (COVID-19) isolation has altered individuals’ food purchasing behaviour and dietary intake patterns. Therefore, this study aims to investigate the changes in dietary intake patterns and their impacts on the weight status of young adults in Malaysia during the COVID-19 lockdown. Methods: This cross-sectional study involved 1045 young adults in Malaysia. The changes in dietary intake patterns were assessed using the Dietary Diversity Questionnaire with slight modifications, while anthropometric measurements including body height, body weight before the pandemic and current body weight were self-reported. Results: Overall, nearly half of the respondents (48.8%) gained weight during the confinement, with an average increment of 4.06 ± 3.23 kg. Of 1045, 45.3% reported consuming more fruits and 60.2% had higher plain water intake during the pandemic. It is observed that 41.0% to 66.8% of the young adults changed their dietary intake patterns during the pandemic. Increased consumption in cereals and grains (β = 0.084, p = 0.015, 95% CI = 0.017–0.160), as well as oils and fats (β = 0.123, p = 0.001, 95% CI = 0.059–0.241), was positively associated with weight gain during the pandemic. On the contrary, an increased plain water intake was negatively associated with weight gain during the lockdown (β = −0.100, p = 0.003, 95% CI = −0.171–−0.034). Findings in the current study also suggested that cutting back cereals and grains (β = 0.156, p < 0.001, 95% CI = 0.122–0.288), as well as oils and fats (β = 0.091, p = 0.012, 95% CI = 0.022–0.183), contributed significantly to weight loss during the pandemic confinement. Conclusion: In conclusion, the enforcement of the Movement Control Order (MCO) drove up the prevalence of overweight/obesity among young adults in Malaysia. Increased consumption of cereals and grains and oils and fats contributed to weight gain in the pandemic lockdown. Nonetheless, a noticeable proportion of young adults in Malaysia shifted to a healthier food choice by increasing the consumption of fruits and vegetables.