NEW YORK (Reuters Health) - People with diabetes who ate a diet consistent with general health guidelines and high in fruit, vegetables, fiber and unsaturated fat were less likely to develop kidney disease than unhealthy eaters, in a new study.
Researchers also found that eating normal amounts of salt and protein was not tied to a higher risk of kidney disease or death - despite doctors traditionally recommending people with diabetes go easy on those nutrients.
"Most of the recommendations we give are opinion-based, I think," Dr. Rainer Oberbauer, who worked on the study at the Medical University of Vienna in Austria, said.
"Since there are no randomized trials on the other parameters that they usually recommend such as salt restriction, fruits, vegetables and so on, doctors recommend what's kind of logical and intuitive without any real data."
Among people with diabetes, high amounts of sugar in the blood can lead to kidney damage over time. So can high blood pressure, which often accompanies diabetes.
For the new report, Oberbauer and his colleagues followed about 6,200 people aged 55 and older with diabetes and no advanced kidney problems. Those people were part of a larger multi-country study on diabetes and vascular disease funded by the pharmaceutical company Boehringer Ingelheim.
Participants filled out questionnaires about how often they ate a range of foods. The researchers plotted those responses on a healthy eating scale of 0 (lowest quality) to 90 (highest quality).
People in the study had an average diet score of 24.6, with a range of 9.8 to 66.2.
Over the next five and a half years, about 32 percent of study participants developed kidney disease and eight percent died.
Oberbauer and his colleagues found that participants who scored in the top one-third for overall diet were 26 percent less likely to be diagnosed with chronic kidney disease and 39 percent less likely to die during the study period than those in the bottom one-third.
That was after taking into account their age, gender and how long each person had had diabetes.
Moderate drinking - about five alcoholic drinks per week - was tied to a lower risk of chronic kidney disease, as was eating more animal protein.
Sodium, measured from a urine sample, was not linked to a person's chance of developing new or worsening kidney disease except at very high or low levels.
The results don't prove that eating a healthier diet can ward off kidney problems.
But, the researchers wrote in JAMA Internal Medicine, "If the associations identified would be causal, then for each 1,000 individuals with type 2 diabetes and vascular disease adhering to a healthy diet, 131 would be expected to experience incidence or progression of (chronic kidney disease) within the next 5 years compared with 151 individuals on an unhealthy diet."
Dr. Holly Kramer, who studies nutrition and kidney disease at Loyola University Chicago, said the study had a number of limitations - including that sodium was measured in the urine at a single time point, rather than over one or more days, and that the researchers didn't have data on the total amount of calories people ate each day.
However, she said the findings are consistent with past studies showing that fruit and leafy green vegetables, in particular, are beneficial.
"You really need to look at all of the results together and summarize what is consistently found, and use that to determine nutritional guidelines," Kramer, who co-wrote an editorial published with the new study, told Reuters Health.
That research "consistently shows that if you eat fresh fruits, vegetables, low-fat dairy products, that that is helpful," she said. "And eating more of the American-style (diet), which is red meat, fat, sugar, is not beneficial and increases the risk of kidney disease."