The COVID-19 pandemic significantly impacted daily life, disrupting routines and altering lifestyle behaviors. This study aimed to investigate changes in body weight, nutritional status, and weight loss practices among adults in Türkiye during the first year of the pandemic. A cross-sectional online survey was conducted between March and April 2021, including 806 participants. Height and weight were self-reported, and weight loss practices, along with their details, were evaluated. A qualitative component explored participants’ perceptions of weight change, with 274 valid responses. The mean weight gain during the pandemic was 0.88 kg (p < 0.001). Among participants, 44.9% reported weight gain, 22.6% reported weight loss, and 14.1% experienced weight fluctuation. Among those who experienced weight fluctuations, 47.4% resulted in weight loss, 14.9% showed no change, and 37.7% experienced weight gain. The prevalence of overweight increased from 19.2% to 22.8%, and obesity rose from 8.7% to 9.4% (p = 0.005). Regarding weight loss practices, 30.1% of participants engaged in physical exercise, while 25.7% reported following weight loss diets. Qualitative analysis revealed that changes in physical activity, eating habits, and psychological factors were key determinants of weight change. These findings emphasize the diverse effects of the pandemic on weight status and management.