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NEW YORK, Sept. 28 (UPI) -- Physical fitness and avoiding weight gain may be more significant than shedding pounds to prevent kidney disease in obese adults, a new study indicates. The findings, published Thursday in the journal Obesity, came from researchers at Drexel University's College of Medicine and Dornsife School of Public Health in Philadelphia.
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Previous studies found an association between weight gain and higher chronic kidney disease risk, but this study is among the first to explore the role of physical fitness and chronic kidney disease risk in an obese population without diabetes or kidney disease as a baseline.
"Over 40% of U.S. adults have obesity, which is an independent risk factor for kidney disease," the study's lead author, Dr. Meera N. Harhay, told UPI via email.
Harhay is a professor of medicine in the Department of Medicine at Drexel University College of Medicine.
"Most studies that have looked at kidney disease risk factors in obese adults have focused on those with diabetes or other risk factors, such as cardiovascular disease," she said. "But many adults with obesity don't have diabetes and might be otherwise healthy."
Unlike most previous research on physical activity and chronic kidney disease risk, the adults in this study did not have diabetes, heart disease or reduced kidney function at baseline.
More than 1 in 7 U.S. adults -- some 37 million -- suffer from chronic kidney disease. Estimates indicate that 9 out of 10 of these people are unaware that they have the disease.
Deaths from chronic kidney disease are rising nationally, from 91.7 per 1,000 in 2019 to 100.6 per 1,000 in 2020 -- with higher increases among Black and Hispanic populations.
Treating patients is also taxing for the nation's health care system, with more than $85 billion spent by Medicare alone in 2020. As of February, 88,658 people were on the waiting list for a life-saving kidney transplant in the United States.
The researchers followed 1,208 overweight and obese adults from six cities nationwide who were participants in the National Institutes of Health-sponsored Multi-Ethnic Study of Atherosclerosis.
Volunteers were recruited from July 2000 to August 2002 and followed over a median of nine years, during follow-up exams at 18 months, three years, five years and 10 years.
Investigators found an association between weight gain and a higher risk of chronic kidney disease. Specifically, each 5 kilograms of weight gain from baseline was associated with a 1.34 times higher rate of developing chronic kidney disease.
This increase was measured by blood tests of estimated glomerular filtration rate, or eGFR, using a formula that factors in both cystatin C -- a protein produced by cells -- and serum creatinine, which kidneys filter out of blood through production of urine. High levels of cystatin C and serum creatinine signal poor kidney function.
The group also examined how physical fitness, as indicated by walking pace, was linked to kidney function.
A slow walking pace (under 2 miles per hour) -- as self-reported in surveys at each visit -- was associated with more rapid kidney function decline.
Patients with a slower pace are at higher risk for developing chronic kidney disease than faster-walking individuals. The findings were similar whether or not patients had high blood pressure at baseline.
"We found that individuals who gained weight and those who had slow gait speed, a marker of low physical fitness, developed kidney disease faster than those who had stable weight and higher fitness," Harhay said.
"Also, interestingly, kidney disease risk was similar between those who maintained their weight and those who lost weight. Our results tell us that preventing weight gain and improving physical fitness are important strategies to mitigate kidney disease risk among obese adults.
"Weight loss is probably helpful for many other reasons, but we should emphasize the importance of fitness and being able to maintain one's weight instead of gaining further."
The study population included individuals with obesity from numerous racial and ethnic backgrounds and ages who did not have kidney disease or diabetes or other known cardiovascular disease at baseline.
"Therefore, our results may not be generalizable to adults with these risk factors," Harhay said. "Our study also did not include those with extremely severe obesity --over 300 pounds."
Even though researchers did not see an association between weight loss and lower chronic kidney disease risk, Harhay added that kidney-related health benefits are likely from weight loss in this population, such as improvements in glycemic and blood pressure control.
Dr. Reshmi Srinath, who was not involved in the study, told UPI via email that "these results are very reliable."
Srinath is an assistant professor in the division of endocrinology, diabetes and bone disease at Mount Sinai Health System in New York. She also is director of the Mount Sinai Weight and Metabolism Program.
"This study provides compelling evidence about the association between obesity, continued weight gain and development of kidney disease in a large, multi-ethnic cohort," she said.
"Slow gait was also shown to have association with risk of kidney disease, which demonstrates the importance of physical functioning and risk of morbidity."
Srinath added that while most studies focus on risk of diabetes and cardiovascular outcomes, more data is needed that assesses the risk of developing kidney disease. Clinicians "need to be better about monitoring kidney function in those with weight gain."
Dr. Marie Nevin, who was not involved in the research, told UPI that it was a "solid study" based on its size and 10-year duration. Nevin is an endocrinologist with Summit Health in Morristown, N.J.
"These findings are significant because this points to the fact that patients, through their own efforts of not gaining weight and physical activity, can positively impact their risk for kidney disease," she said.
"Since chronic kidney disease may ultimately have such a negative impact on patients' quality of life, knowing that lifestyle modification could potentially improve this outcome is very helpful."
However, she added that "it is an interesting and perhaps a surprising result, that weight loss was not necessarily protective of kidney disease. This will have to be confirmed in larger studies."
