This is an observational study with no active intervention implemented. Its primary aim is to analyze the relationship between the Composite Dietary Antioxidant Index (CDAI) and overweight/obesity, as well as the associated metabolic abnormalities, using the dataset-with no experimental manipulation involved.

Body Mass Index (BMI) will be calculated as weight (in kilograms) divided by the square of height (in meters). According to the World Health Organization's classification, a BMI of 25.0 - 29.9 kg/m² is considered overweight, and a BMI of 30.0 kg/m² or higher is considered obese. Data on weight and height will be obtained from the NHANES dataset.

Metabolic phenotypes are classified as metabolically healthy or unhealthy based on the components of metabolic syndrome defined in the third report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). Waist circumference data is not used in this classification due to its high correlation with BMI.

A participant is defined as metabolically healthy if they have none or only one of the following four metabolic abnormalities: (1) Serum triglycerides (TG) ≥ 150 mg/dL; (2) Serum high-density lipoprotein cholesterol (HDL-C) < 40 mg/dL in men or < 50 mg/dL in women; (3) Fasting glucose ≥ 100 mg/dL or use of hypoglycemic drugs; (4) Blood pressure ≥ 130/85 mmHg or use of antihypertensive drugs.

A participant is defined as metabolically unhealthy if they have two or more of the above metabolic abnormalities. Relevant data will be retrieved from the NHANES database.