Obesity is a medical condition in which the accumulation of excess body fat may have a negative impact on an individual’s health that increases the risk of various diseases or potentially reduces life expectancy. Worldwide there are 1.5 billion overweight or obese adults, a number that is expected to reach three billion by 2030. More than 34.9 % of adults (age ≥ 20 years) and 17 % of youths (age 2–19 years) and 8.1 % of infants and toddlers in the United States are obese. The prevalence of obesity in United States is high and has remained stable [1]. The health risk of obesity in United States has been associated with many diseases. Obesity-related conditions include, type 2 diabetes, hypertension, heart disease, high cholesterol, hypertension, stroke and cancer. The costs associated with obesity in the United States are exponential. In 2008, the estimated annual medical cost of obesity in the United States was $147 billion. The average medical costs for people who are obese are $1,429 higher than those individuals of normal weight in 2006 [2].

On the other hand, approximately 10 % of men and 5 % of women developed kidney stones in their lifetime and more than $2 billion are spent annually on treating stone disease. Among other health related issues, there is a strong association between obesity and stone disease. Many studies have shown a direct correlation between obesity and stone disease. This chapter will examine the Association between obesity and the risk for developing nephrolithiasis.

Obesity and weight gain are both associated with an increased risk of kidney stones. Men weighing more than 220 lb and women weighing more than 150 lb were 44 and 90 %, respectively, more likely to develop stone disease than individuals weighing less than these body weights. Both men and women who gained more than 35 lb after the after 21 years of age were 39 and 82 %, respectively, more likely to develop calculi than individuals who did not gain weight. Among women, younger and older women who gained 35 lb had an 82 and 70 %, respectively, higher risk of forming stones than those whose weight did not change. These studies demonstrate the strong link between obesity and formation of stone disease [3].

Body mass index (BMI) is used to measure weight and height to indicate obesity. For example, for adult men and women with a BMI between 18.5 and 24.9 is considered healthy; an adult with a BMI between 25 and 29.9 is considered overweight and a BMI of ≥30 is considered obese.

Higher BMI’s and larger waist circumferences are both risk factors for kidney stones. Researchers think that there may be a link between fat tissue, insulin resistance, and urine composition. People with larger body sizes may excrete more calcium and uric acid, which increase the risk of kidney stone formation. BMI is shown to be associated with both an increased prevalence of nephrolithiasis and with larger stone sizes [4].

Waist circumference is one of the simplest and most often used measure of abdominal obesity. Women with a waist size ≥35 in. and men with a waist size ≥40 in. are considered to have abdominal obesity.

Waist circumference was correlated with an increase risk of stone formation in men and women. The relative risk (RR) of forming stones in men with larger waist (>43 in.) compared to smaller waist (<34 in.) was 1.48 [3]. In older and younger women, the RR to form stones with larger waist (>40 in.) compared to smaller waist (<31 in.) was 1.71 and 1.94, respectively [3].