It has been estimated that almost half of gout patients in Europe are obese.1 BMI is strongly correlated with serum urate (SU),2 and weight loss in people without gout has been shown to decrease SU.3 Hyperuricaemia is a critical factor in the development of gout, which is caused by deposition of monosodium urate crystals in the joints and tissues. Hence, lowering SU is considered central in the long-term management of gout. The recommended target for SU is <360 μmol/L (<6 mg/dL), and if this is sustained over time, it leads to dissolution of monosodium urate crystals, reduction in gout flares, and resolution of tophi.
Even though weight loss is commonly recommended for gout,4 no one has previously conducted a systematic review investigating the effects of weight loss. Therefore, our objective was to determine the benefits and harms associated with weight loss in overweight and obese gout patients.
Following our protocol, we searched four electronic databases and two trial registries. We included longitudinal studies with ≥10 overweight or obese gout patients, where the effects following weight loss (intentionally or unintentionally) were quantitatively estimated. We specified 11 outcomes for data-extraction. During the process, we realised that the planned meta-analyses were not possible, because the studies were too heterogeneous. Thus, we decided to summarise the results from each study. The internal validity and the quality of evidence were assessed using the ROBINS-I tool5 and the GRADE approach,6 respectively.
We included 10 eligible studies. Only sparse data were available, and the most frequently reported outcomes were SU, achieving SU target (<360 μmol/L), and gout flares. Only one of the included studies was a randomised controlled trial, and four of the studies had no comparison group. Interventions included intentional weight loss from dietary changes with or without increased physical activity, bariatric surgery, and unintentional weight loss from a high protein diet, metformin, and diuretics. Three studies stratified cohorts according to weight change. Follow-up ranged from 4 weeks to 7 years, and mean weight loss ranged from 3–34 kg. In the risk of bias assessment, none of the studies were rated low risk for all seven bias domains, and four of the studies were rated critical risk for the first bias domain (bias due to confounding issues).
At the latest follow-up, the studies reported a change in SU ranging from -168 to +30 μmol/L. For those with SU above target at baseline, between 0 and 60% achieved target SU. Gout flares were reported in different ways, but overall, six out of eight studies reported beneficial effects. For all three outcomes (SU, achieving SU target, and gout flares) dose-response relationships were reported. However, it should be noted, that in the short term, two studies reported a temporary increase in SU and gout flares following bariatric surgery. We rated the quality of evidence for the three outcomes to be low, moderate, and low, respectively, because we downgraded for study types, risk of bias, and upgraded for dose response relationship, and large reported effects. In conclusion, the available evidence indicated beneficial effects of weight loss for overweight and obese gout patients, although short-term, unfavourable effects may occur. Since the current evidence consists of only a few studies (mostly observational) of low methodological quality, there is an urgent need to initiate rigorous randomised controlled trials.