BACKGROUND: A silent intragenic polymorphism (1359 G/A) of the cannabinoid receptor 1 gene resulting in the substitution of the G to A at nucleotide position 1359 in codon 435 (Thr) was reported as a common polymorphism in Caucasian populations. Intervention studies with this polymorphism have not been realized. OBJECTIVE: We decide to investigate the role of missense polymorphism (G1359A) of cannabinoid receptor 1 gene on adipocytokines response and weight loss secondary to a low-fat versus a low-carbohydrate diet in obese patients. DESIGN: A population of 249 patients was analyzed. A nutritional evaluation was performed at the beginning and at the end of a 3-month period in which subjects received one of two diets (diet I: low fat vs. diet II: low carbohydrate). RESULTS: One hundred forty three patients (57.4%) had the genotype G1359G (wild-type group), and 106 (42.6%) patients had G1359A (92 patients, or 36.9%) or A1359A (14 patients, or 5.6%; mutant-type group). With both diets in wild-type and mutant-type groups, body mass index (BMI), weight, fat mass, waist circumference and systolic blood pressure levels decreased. With both diets and in wild-type group, glucose, total cholesterol and insulin levels and homeostasis model assessment test score decreased. No metabolic effects were observed in mutant-type group. Leptin levels decreased significantly in the wild-type group with both diets (diet I: 10.8% vs. diet II: 28.9%; P<.05). CONCLUSION: The novel finding of this study is the lack of metabolic improvement of the mutant-type groups G1359A and A1359A after weight loss with both diets. Decrease in leptin level was higher with low-carbohydrate diet than low-fat diet.