The research group added isolated soy protein to the diets of 14 military veterans - who were under treatment for advanced stages of type 2 diabetes - and claimed that at the end of the treatment the men all had significantly fewer unwanted proteins in their urine and slightly higher "good" HDL cholesterol levels in their blood.
"The number of type 2 diabetics is increasing to epidemic proportions, with the disease being found in younger and younger individuals everyday," said Sandra Teixeira, who worked on the study, which is published in the August issue of the Journal of Nutrition.
As she pointed out, this also means that more people are suffering from kidney and cardiovascular disease as a result of their diabetes.
"Our most remarkable result was that soy protein added to the diet, instead of animal source protein (in this case casein), resulted in a significant reduction in the amount of protein in the urine," said John Erdman, a professor of nutrition at the University of Illinois College of Medicine. "Patients eating casein actually had an increase of urine protein levels."
The men who participated in the study were aged between 53 and 73 and consumed pre-measured amounts, based on their weight, of either vanilla flavored isolated soy protein made from soybeans or casein, as part of additional dishes or drinks in their diet.
"Our hypothesis was that we could slow down or maintain protein levels in the urine by introducing soy protein," said Lea Ann Carson, a research dietitian in the department of food science and human nutrition at Illinois. "We actually saw a reduction in these levels."
The researchers reported that those consuming the soy protein had a 9.5 per cent reduction in the excretion of urinary albumin, an undesired buildup of globular protein indicative of worsening kidney function, while participants eating casein had an 11.1 per cent increase in urinary albumin.
Moreover, levels of "good" HDL cholesterol improved by 4.3 per cent, though overall cholesterol ratios improved only slightly. HDL dropped just fractionally in the men who consumed casein.
"The results suggest that a dietary modification as easy to implement as consuming soy-protein-rich foods may help to prevent diabetic kidney disease in addition to improving blood-lipid profile," said Teixeira. "This is quite important in light of the growing diabetic population, and larger trials are warranted to confirm the findings."
The researchers were unable to explain why the soy protein worked as it did. Erdman said that isoflavones, estrogen-like components in soy, may play a role as they are thought to have improved blood lipids in earlier soy studies.
Alternatively, he noted they had observed an elevated level of serum arginine - a chemical precursor to nitrogen oxide that dilates arteries - in the men, and suggested that arginine may improve blood flow in the kidney.
However this is not the first time a link has been made between soy protein and diabetes. Iranian researchers suggested last year that soy protein could help diabetes patients protect their hearts and kidneys from damage caused by the disease.
A crossover randomized clinical trial was conducted on 14 type 2 diabetes patients (10 men, four women) with nephropathy (diabetes-related kidney damage) in Tehran. The patients were asked to follow a diet typically recommended to control nephropathy including 0.8 g/kg protein - based on 70 per cent animal and 30 per cent vegetable protein - for seven weeks.
After a washout period of four weeks consuming the pre-study diet, subjects were readmitted to repeat the same cycle with a similar diet containing 35 per cent soy protein and 30 per cent vegetable protein.
The patients were found to have experienced significant reductions in total cholesterol, triglyceride and LDL-cholesterol after following the soy diet. And the researchers reported a favourable effect on renal function.
The incidence of type 2 diabetes is climbing rapidly in Europe as the population becomes increasingly overweight. Researchers have warned of the impact on healthcare of the many side effects of obesity, including type 2 diabetes, heart disease and cancer.
Currently, 5-10 per cent of the world's healthcare budget is spent on diabetes, and by 2025 this figure could reach 40 per cent in some countries if predictions of diabetes prevalence are fulfilled. Most of the economic costs of diabetes are attributable to the various complications linked to it, with up to two-thirds of people with diabetes in certain countries developing serious chronic complications.
The International Diabetes Federation and World Health Organisation emphasise the benefits of a healthy lifestyle (eating a well-balanced diet, stopping smoking, and exercising regularly) in the prevention of diabetes.