Background: Childhood obesity and its complications are serious health problems and diet/lifestyle changes can be beneficial for the prevention of diseases. Adaptation of the Healthy Lifestyle-Diet (HLD) Index in accordance with the dietary guidelines for Turkey (TR) and determination of the relationship between metabolic syndrome risk factors in obese children were the aims of this study. Methods: This study was conducted on 164 overweight or obese children (87 male, 77 female) aged 9–13 years. For all participants, the HLD-TR Index and a 24-h dietary recall were performed and the mean adequacy ratio (MAR) was calculated. Anthropometric measurements and the body composition of the children were taken. Metabolic syndrome risk factors and insulin resistance were assessed. Results: The mean age of the male and female children was 11.2±1.49 and 11.0±1.40 years, respectively. The majority of the children were obese in both genders. There were no statistically significant differences in the HLD-TR scores between the genders. As the index scores increased, a decrease in the energy intake and an increase in the MAR were observed. Negative correlations between the index scores and body mass, waist circumference and body fat mass were observed. Furthermore, a one-unit increase in the index score decreases the insulin resistance risk by 0.91 times after adjustments for age and gender (odds ratio: 0.91 [0.85–0.97]). Conclusions: The HLD-TR Index is a valid tool that can give an idea about the quality of the diet in obese children. Furthermore, with the increase in the compliance with recommendations for diet/lifestyle changes, indicators of obesity and metabolic syndrome were decreased.