Healthy Diet Lowers CKD Risk in Type 2 Diabetes Patients

Miriam E. Tucker

August 13, 2013

A diet full of fruits and vegetables appears to slow the development of chronic kidney disease (CKD) in high-risk patients with type 2 diabetes, but protein and sodium intake has little effect, a new observational study has found.

The results, from a substudy of the Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial (ONTARGET), were published online August 12 in JAMA Internal Medicine by Daniela Dunkler, PhD, from McMaster University, Hamilton, Ontario, and colleagues.

"The absolute novelty is that we…elucidated the associations of diet on the incidence of kidney disease in patients with diabetes," principal investigator Rainer Oberbauer, MD, professor of medicine at the University of Vienna, Austria, told Medscape Medical News. The finding of a lack of effect for protein and sodium intake was somewhat surprising, he said, given that it counters long-held dogma. "We were all taught the mantra of protein restriction and prevention of progression."

However, he cautions, "It is of note that our study is an observational study, and causal inference is not justified from these findings."

But the authors, as well as an editorial accompanying the paper, by Holly Kramer, MD, from Loyola University, Chicago, Illinois, and Alex Chang, MD, from Johns Hopkins University, Baltimore, Maryland, agree that the study, albeit with limitations, nonetheless points to clear benefit for consumption of fruits and vegetables and for moderate alcohol intake.

"Perhaps the best dietary advice we can give patients with type 2 diabetes and kidney disease is the same as the advice for those who want to avoid chronic kidney disease and the same dietary advice for everyone: eat a diet rich in fruits and vegetables, low-fat dairy products, and whole grains while minimizing saturated and total fat," Drs. Kramer and Chang write.

Healthy Diet Reduced CKD by 26%, Cut Death by 39%

Dr. Oberbauer and colleagues explain that little is known about the influence of diet on the incidence or progression of CKD in individuals with type 2 diabetes.

They assessed 6213 participants from ONTARGET who had type 2 diabetes and either normoalbuminuria or microalbuminuria at baseline. ONTARGET originally enrolled 25,620 participants aged 55 and older who either had either vascular disease or type 2 diabetes with end-organ damage and so were at high risk for kidney disease.

The substudy's primary outcome was 1 of 3 states at 5.5 years of follow-up:

  • Alive with no incidence or progression of  CKD.

  • Alive with incidence or progression of CKD.

  • Deceased.

"Incidence or progression" of CKD was defined as at least 1 of the following events: new microalbuminuria, new macroalbuminuria, a glomerular filtration rate decline of more than 5%/year, or end-stage renal disease.

Of the patients, 31.7% (1971) were alive with incidence or progression of CKD and 8.3% (516) had died after 5.5 years.

Diet was assessed with the modified Alternate Healthy Eating Index (mAHEI), a measure of adherence to dietary guidelines, with a higher score indicating greater consumption of healthful foods such as vegetables and lower consumption of unhealthy items such as fried foods.

Several statistical models were used to account for confounders, including age, diabetes duration, albuminuria status, sex, ONTARGET randomization arm, body mass index (BMI), blood pressure, glucose level, and previous antihypertensive use.

High scores on the mAHEI were significantly associated with reduced CKD risk. The mean score for those with no renal event was 25.23, vs 23.42 among those who died (P < .001).

Those in the highest mAHEI tertile had a significantly 26% lower risk for CKD progression compared with the lowest tertile (odds ratio [OR], 0.74). The risk for death was reduced by 39% for those in the highest vs the lowest tertile (OR, 0.61).

"Because participants with a healthier diet lived longer, they had a longer period during which to develop the renal outcome, but it occurred less frequently," the authors note.

Protein Intake Unexpectedly Linked to Lower CKD Risk

Greater consumption of both total and animal protein was associated with a lower risk for CKD progression, with an OR of 0.86 for the highest vs the lowest tertiles of mAHEI.

While this finding was unexpected, previous data suggesting an increased risk for CKD with greater protein intake have typically focused on later-stage CKD, Dr. Dunkler and colleagues point out.

Alcohol was consumed by 32.6% of the study population. ORs for the highest vs lowest tertiles were 0.75 for CKD progression and 0.69 for mortality. The association between alcohol and CKD was J-shaped, with a greater risk occurring after about 20 drinks per week.

"Moderate alcohol consumption may serve as a proxy for social integration and overall subjective well-being but may also act through direct vascular effects," the authors note.

Higher 24-hour potassium excretion was associated with reduced risk for CKD (OR, 0.78 for highest vs lowest tertile), but sodium excretion was not associated with risk for CKD, even after researchers controlled for the effects of sodium on blood pressure. There was a U-shaped relationship between sodium excretion and mortality, just as was seen in the overall ONTARGET study population.

Clinical Implications: Stick to a Healthy Diet

According to Dr. Dunkler and colleagues, this study showed that the 2 main nutritional recommendations for people with CKD — a low-protein diet and a low-sodium diet — did not reduce the incidence and progression of kidney disease.

"Although the finding was not causally shown, it may be legitimate to advise individuals with type 2 diabetes and vascular disease to adhere to a healthy diet avoiding extremes of protein and salt intake to reduce their high risk for renal disease and death," they stress.

Indeed, such advice is appropriate to prevent cardiovascular disease, they note. The editorialists agree, noting that the Mediterranean-style diet employed in the PREDIMED randomized study published earlier this year decreased the incidence of major cardiovascular events in individuals with diabetes or at least 3 cardiovascular risk factors.

"In summary, our findings indicate that a healthy diet is associated with a reduced risk of developing CKD and slower progression of early kidney disease among individuals with type 2 diabetes," Dr. Oberbauer and colleagues conclude.

Dr. Oberbauer heads a lab at the university that conducts academic research in genetic and clinical epidemiology of kidney disease. Among the lab's major projects is a CKD European Union–wide collaborative called SysKid, which funded the current observational trial. The ONTARGET trial itself is funded by Boehringer-Ingelheim. Dr. Dunkler and colleagues, Dr. Kramer, and Dr. Chang have reported no relevant financial relationships.

JAMA Intern Med. Published online August 12, 2013. Abstract Editorial

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