In this study, we investigated the correlation between serum uric acid and body fat before and after weight loss in obese children and adolescents. The results showed that a combination of aerobic exercise and appropriate caloric control can help reduce weight, especially FM. Importantly, we found that UA was associated with BMI, FM, and FFM with adjusting age and gender, and played an important role in weight loss.
To date, the research on weight loss methods is roughly divided into dieting, exercise, meal replacement, drugs and surgical weight loss. Among them, exercise combined with diet intervention is considered to be the most scientific and reasonable way to lose weight [14, 15]. In terms of exercise methods, aerobic exercise is characterized by activities that are fun and have low exercise load intensity, which is more suitable for children. In addition, when the aerobic exercise time exceeds 30 min, the fat decomposition efficiency in the body is increased, and the body functions as a main energy supply material, thereby achieving the effect of weight loss . Aerobic exercise not only helps to reduce fat and retain muscle , but also improves glucose and lipid metabolism [17, 18]. Likewise, our results showed that after a 6-weeks weight loss interventions, participants' weight and body fat were significantly reduced, while muscles were little increased. The average weight loss in obese children was 10.30 kg (12.07%) consisting of 9.92 kg of FM, which was more evident than in many other studies.
Globally, the incidence of hyperuricemia is estimated to be about 2.0–3.1%, and it is higher in men than in women [19,20,21,22]. With the increase in the incidence of childhood obesity, it is one of the reasons for the increase in the incidence of hyperuricemia in obese children . Importantly, a 21-year follow-up study found that obese children were 3.25 times (male) and 3.55 times (female) more likely to develop hyperuricemia than adults of normal weight . However, since the normal range of uric acid depends on age and gender [11, 12], the cut-off points for the diagnosis of hyperuricemia in children and adolescents are also different, which also brings some trouble for pediatricians to diagnose hyperuricemia.
Previous studies have shown that an elevated uric acid levels are associated with obesity, metabolic syndrome, hypertension and disorders of glucose and lipid metabolism in childhood [24, 25]. In addition, studies in adults indicated that hyperuricemia is positively associated with BMI, WC, and body fat, but is also positively associated with muscle [9, 26]. Surprisingly, the results from our study found that uric acid in obese children and adolescents was not only positively related to BMI, FM, and FFM, but also to the decrease in FM during weight loss. To the best of our knowledge, this result is first reported herein and is a highlight of our research.
However, the pathophysiological mechanism involved in the occurrence of hyperuricemia in obese children is not yet clearly established, and the mechanism of the effect of UA on body fat is also not yet fully understood. Previous study indicated that hyperuricemia induced inflammation of fat cells and oxidative stress. And fat cell inflammation and oxidative stress were the key mechanisms for fat mice to develop obesity and metabolic syndrome . In addition, as for the association between blood uric acid and TC and TG, significant relationship was found in this study with adjusting for age and gender before and after intervention. This might imply that high uric acid affected the redistribution of adipose tissue by inducing the abnormality of lipids metabolism.
In light of the findings of this study, we should pay close attention to blood uric acid levels during weight loss in obese children, which may be a sensitive and useful signal indicator. However, for obese children diagnosed with hyperuricemia, whether uric acid lowering treatment is needed before weight loss should be considered and further researched. But it was worth mentioning that our research found that reasonable diet and exercise can reduce uric acid by 53 mmol/L.
Of course, the limitations of this study should be considered. First, the sample size of this study is small, and it is difficult to elaborate the mechanism of uric acid on body fat. Second, clinical data were only monitored and evaluated before and after the intervention. Finally, this study did not follow up on the effects of aerobic exercise combined with dietary weight loss on children's long-term quality of life and health status.