Does Dietary Treatment Cause Obesity in Phenylketonuria? Comparison of Obesity Ratios of Patients Receiving Dietary Treatment and Tetrahydrobiopterin Treatment

Phenylketonuria is treated either with tetrahydrobiopterin (BH4) or with a phenylalanine-restricted diet. Patients in the diet group may tend to consume carbohydrate-rich foods which have a risk for obesity. In this study, the prevalence of obesity+overweight among phenylketonuria patients either treated with phenylalanine-restricted diet or with BH4 were compared.Patients with phenylketonuria were divided into two groups on dietary treatment and BH4 treatment. Body mass index (BMI), BMI-percentile, and z-score values of patients were calculated and classified as underweight, normal-weight, overweight, and obese according to their nutritional status. The annual mean phenylalanine level of each patient is also evaluated. The study was done retrospectively.A total of 130 patients was included. 77 were receiving diet (female (n,%):37, 48.1%; male (n,%):40, 51.9%) and 53 were receiving BH4 (female (n,%):33, 62.3%; male (n,%):20, 37.7%) respectively. According to BMI-z-score, the sum of the ratio of obesity+overweight was found to be 35.1% in the diet group, 16.9% in the BH4 group. Ratio was significantly higher in diet group (p=0.02). When obesity+overweight ratios were examined in terms of female/male distribution, no significant difference was found. Considering the correlation of obesity+overweight ratios with age in two groups, the median age of the patients with normal weight+underweight in the BH4 group were found as 46-months, and the median age of obese+overweight patients was 137-months (p=0.001). For the same situation, there was no significant difference in the dietary treatment group (p=0.92). Mean annual phenylalanine levels were significantly higher in obese+overweight patients (p=0.047) in the BH4 treatment group but this difference was not significant in the diet group (p=0.051).Patients on the phenylalanine-restricted diet have a risk of obesity or overweight. Therefore, attention should be paid not only to the phenylalanine levels of these patients but also to their weight control and dietary content