Fluctuating body weight may worsen insulin resistance — and insulin resistance can, in turn, stress the kidneys and harm kidney tissue.
Obesity is a risk factor kidney disease, and people who are heavy are often advised to lose weight to possibly improve their chances of avoiding kidney disease and a host of other problems. One problem with weight loss, though, is the up-and-down pattern of it as people who are successful in dropping pounds often wind up gaining them back. The “yo-yo” effect of weight loss carries its own set of risks, contributing perhaps to the development of diabetes in some people and the risk of morbidity and mortality of coronary heart disease.
In the December issue of the journal Obesity, a team of Korean researchers led by Young Su Joo of Yonsei University in Seoul reported results of a longitudinal study that added to the evidence that body weight fluctuations are unhealthy. Their results showed that up-and-down body weight was associated with a decline in kidney function that could portend chronic kidney disease.
Joo and colleagues found that the risk of rapid decline in kidney function (as measured by the estimated glomerular filtration rate [eGFR]) was significantly higher among people with greater fluctuations in body weight than those whose body weight was steadier. More specifically, the risk of rapid decline in kidney function (defined for the purposes of this study as an annual eGFR decline of greater than 3 ml/min/1.72 m2 per year) was 48% higher in the group with greatest body weight fluctuation compared with the group with the lowest. After the statistical adjustments for education, income, physical activity, blood pressure and other factors, the difference decline in kidney function between the high and low fluctuation group was even greater at 66%.
This is an epidemiological study not an investigation into the pathophysiology of weight loss fluctuations. But Joo and colleagues offered several possible explanations for how yo-yoing weight might harm kidneys. Up-and-down body weight worsens insulin resistance, and insulin resistance has the effect of increasing oxidative stress and other processes that harm the kidneys, they said. Body weight fluctuations may also have an effect on the blood pressure that stresses the kidney.
Joo and colleagues conducted this study with data extracted from the Korean Genome and Epidemiology Study, a prospective study that tracked people in an urban and rural area of Korea. They excluded people with known kidney disease and cancer, so the study cohort was narrowed down to just under 6,800 people. They had data from median follow-up period of almost 12 years too to work with. People in the study were weighed periodically, so the researchers used differences in body weight between those periodic weight measurements to arrive at a statistic for average successive variability (ASV) for weight. Then they divided the 6,800-member cohort into the highest, medium and lowest tertiles of ASV.
During the dozen years that people were followed, rapid eGFR decline indicative of kidney disease occurred in 913 of the entire group included in this study, which works out to 13.4% (913 out of 6,790). In the tertile with lowest weight variability, the prevalence of rapid eGFR was 12.5% and in the tertile with highest, it was 16.3%. The researchers also calculated that each 1-kilogram increase in the ASV translated into a 24% increase in the risk of rapid eGFR decline, and they noted that the relationship between rapid eGFR decline and ASV was strong even after adjustment was made for confounding factors.