The goal of this observational study is to investigate the relationship of CLOCK 3111T/C (rs1801260) gene variant with nutritional habits, nutritional status, chronotype, sleep quality, some biochemical parameters in overweight or obese individuals and to observe its effect on weight loss diet intervention. The main questions it aims to answer are: * Is the frequency of carrying the CLOCK 3111T/C (rs1801260) gene risk allele different between individuals with normal body weight and those who are overweight or obese? * Do those with the CLOCK 3111T/C (rs1801260) risk allele have a higher frequency of evening chronotype and a shorter sleep duration? * Is the effect of CLOCK 3111T/C (rs1801260) gene alleles different on weight loss diet response in overweight or obese individuals? A questionnaire will be applied to the individuals in both groups (normal body weight and overweight/obese individuals) to evaluate their general characteristics, eating habits, adherence to Mediterranean diet, DASH and MIND. In addition, anthropometric measurements, 3-day food consumption record and 3-day physical activity record will be taken from individuals. CLOCK 3111T/C (rs1801260) gene variant analysis in whole blood, adiponectin and leptin hormones in serum samples will be studied. Participants those who are overweight/obese will be asked to follow a weight loss diet for 3 months. Researchers will compare participants with normal body weight and those who are overweight or obese to see if there is a difference between the frequency of carrying the CLOCK 3111T/C (rs1801260) gene risk allele.