August 13, 2013
News Review From Harvard Medical School -- Healthy Diet May Protect Diabetics' Kidneys
People with diabetes may be less likely to develop kidney disease if they eat a healthy diet and drink moderately, new research suggests. The study included more than 6,200 diabetes patients. Researchers kept track of them for more than 5 years. In that time, about 32% developed chronic (long-lasting) kidney disease. About 8% died. People who scored highest on a scale measuring the health of their diets were 39% less likely to die than those with the least healthy diets. They were 26% less likely to develop kidney disease. About one-third of those in the study drank alcohol regularly. People who had about 5 drinks per week were 25% less likely to develop kidney disease. They also were 31% less likely to die during the study. The journal JAMA Internal Medicine published the study. HealthDay News wrote about it August 12.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
We often hear that high blood pressure is "the silent killer." But the same can be said for another common condition that gets less attention -- chronic (long-lasting) kidney disease.
Chronic kidney disease means the kidneys have less capacity to filter toxins from the blood and remove them from the body in the urine.
As we age, kidney function declines. Half of American adults over 75 may have below-normal kidney function.
That sounds serious. But kidneys have lots of reserve. Most people's kidneys last many years beyond 75. But it's a different story if you have diabetes.
The risk of kidney disease is four times higher in people with diabetes. And their chance of kidney failure is even greater. Kidney failure results in death unless it is treated with dialysis or a transplant.
Experts have disagreed about the best diet to prevent or avoid worsening of kidney disease in people with type 2 diabetes. This study was designed to help provide answers to this controversy.
The researchers used the two most common tests that measure kidney health:
- Glomerular filtration rate (GFR): This is calculated with a simple blood test. GFR reflects how well the kidneys are filtering out waste from the blood. A normal rate is at least 90 milliliters (3 ounces) of blood filtered per minute. A rapidly falling GFR indicates declining kidney function.
- Urine protein level: Damaged kidneys let proteins pass into the urine. Checking the urine for protein, even at low levels, is an easy way to check for kidney disease.
The researchers identified the diabetics who developed new or worsening chronic kidney disease by using the following measures:
- A 5% yearly average decrease in GFR over 5½ years
- New or higher protein levels in the urine
- Kidney failure
- Death during the 5½-year period
Nearly 32% of the people still alive after 5½ years developed chronic kidney disease. Just over 8% died during that time. The other 60% of the diabetics were alive and did not show any significant kidney function decline.
The researchers then looked at the diets of all the people in the study. The people who ate more than 3 servings of fruit per week had a lower risk of chronic kidney disease. Moderate alcohol intake also was linked to better kidney function.
But the real surprise was the effect of protein consumption. Nutritionists have traditionally told people with kidney disease to stay on a low-protein diet. But this study did not find that was helpful. People with type 2 diabetes who ate low-protein diets had more decline in kidney function than those who ate high-protein diets.
What Changes Can I Make Now?
If you have diabetes, you should have a yearly blood test to determine your GFR and a urine test for protein.
Other studies suggest you can significantly decrease your risk of chronic kidney disease by:
- Maintaining a healthy weight
- Eating limited amounts of red meat
- Avoiding processed meats
- Consuming few, if any, soft drinks
Although this study linked higher protein intake with less kidney damage, many other studies have not supported this. Vegetable protein sources and low-fat dairy products may be safer than animal proteins.
If you have high blood pressure or retain fluid, then you should limit salt. It's unclear if a low-salt diet will help other people with diabetes or mild chronic kidney disease to preserve kidney function. Check with your doctor on this one.
You can help protect your kidneys in other ways as well.
- Don't smoke.
- Keep your blood pressure in the normal range.
- Use caution with medicines that can harm the kidneys. Low doses of nonsteroidal anti-inflammatory drugs such as ibuprofen and naproxen are generally safe. However, people who already have any chronic kidney disease probably should avoid them.
What Can I Expect Looking to the Future?
We can expect experts to continue debating dietary advice for people with diabetes at risk of kidney disease. The results of this study haven't brought any clarity to the issue.
Eating more fruits is consistent with usual dietary advice. But we didn't learn much else from this study. There was no mention of vegetables or whole-grain foods. And the findings regarding the link between higher protein intake and decreased risk of chronic kidney disease go against conventional advice.