Using a definition of obesity as having a BMI greater than 30 kg/m2 (which, in English measurements, corresponds to a 5 foot tall person who weighs 153 pounds, or a 6 foot tall person who weighs 221 pounds), the researchers calculated the incidence of kidney stones in people who were non-obese and in those who were obese. Among the non-obese individuals, 2.6 percent were diagnosed during the study period with kidney stones, compared to 4.9 percent of the obese individuals. When the investigators arranged those in the obese group by their BMIs, ranging from above 30 kg/m2 to more than 50 kg/m2, they found that the increased risk remained constant, regardless of how heavy the individuals were.

Matlaga says that he and his colleagues aren't sure why obese people are more at risk for kidney stones, though metabolic or endocrine factors unique to obesity are likely reasons, along with dietary factors such as a high-salt diet. The researchers plan to study these potential risk factors in subsequent studies.

Source: Johns Hopkins Medical Institutions