Kidney disease is one of the complications of diabetes. In 2008, 44 percent of the new cases of kidney failure were attributable to diabetes. Like diabetes alone, diabetic kidney disease requires dietary modifications.
As kidney disease progresses patients usually need to watch their sodium, potassium and phosphorus intake. In addition, they have often been asked to start to follow a low protein diet. But the use of low protein diets has become controversial with even many nephrologists disagreeing on its importance.
Although still a recommendation of many health care organizations (such as the Academy of Nutrition and Dietetics and National Institute of Digestive and Kidney Diseases), restriction of protein in the diet for preservation of kidney function is felt by many to be unnecessary and perhaps harmful. (Of note: Restriction of protein in the treatment of acute renal failure is still an effective modality of care.)
The origin of this protein-restriction recommendation is two -fold. First, people with advanced-stage kidney disease prior to dialysis have a buildup of nitrogenous waste in their bodies, a product of the nitrogen molecules leftover from protein breakdown during digestion. As the kidneys fail they are unable to excrete these waste products. The excess nitrogen causes symptoms of nausea and vomiting. Reduction of protein helps to ameliorate these symptoms.
Second, a series of animal studies in the 1970s and 1980s demonstrated that reducing protein was able to decrease the pressure on the filter cells in the kidney, thereby improving filtration rates and attenuating the time to dialysis. The drugs used to prevent and treat kidney disease (angiotensin receptor blockers and angiotensin converting enzyme inhibitors) work on this same principle.
When researchers attempted to reproduce the results of animal studies in humans, they were stumped. A large-scale study called the Modification of Protein in Renal Disease (MDRD), completed in the 1980s, did not find any improvement in renal function for those following a low protein diet.
There are definite benefits of low protein diets which may be the reason they are still encouraged. These diets tend to be low in phosphorus and saturated fat. And in addition to often requiring a modification in phosphorus intake, many patients with kidney disease have significant elevations in cholesterol and triglyceride levels.
However, reducing protein in the diet below a certain level can lead to malnutrition. In addition, low protein diets are difficult to follow for most people.
So what constitutes a low protein diet? That too is not well-defined. The recommended dietary allowance (RDA) for protein for adults is .8 grams of protein per kilogram of body weight and the estimated average requirement (EAR) is .66g/kg. (The RDA is set at a level of nutrient intake high enough to meet the needs of all healthy people whereas the EAR is the average amount needed to meet the needs of one-half of all healthy people.) Amounts under .8gm/kg are not encouraged for people with diabetes. This translates into 54 grams of protein per day for a man weighing 150lbs.
This level of protein is significantly under what many Americans eat. Protein intake for adults 19-30 years of age estimated from National Nutrition and Health Examination Survey 2003-2004 (NHANES) data was 91 grams +/-22 grams. In general healthy individuals can accommodate a wide range of protein intakes, however, sustained consumption of very high levels of protein may cause alterations in the metabolism of other nutrients
Protein is found in almost all foods in the diet. Meats, eggs and dairy products contain large amounts of protein; starches and vegetables have small amounts; and fruits and fats have minimal content. Considering that a 3 oz piece of chicken breast contains over 21 grams of protein, it is easy to see how the protein content of a day’s meals can add up, especially for those who eat meat.
Dr. Robert Stanton, head of the renal division at Joslin Diabetes Center, adds, “There isn’t any evidence to support the use of low protein diets for people with type 2 diabetes. The studies done were completed on patients with type 1 and they were either small or inconclusive.”
So if you have kidney disease what should you aim for? If you are a big meat- or dairy-eater, reducing your portions to 3 to 4 oz twice per day is prudent but it may not be necessary to start counting every half cup of rice or green beans you have.
Combining a diet for kidney disease and diabetes is complex and can be frustrating to follow. Making an appointment with a registered dietitian who is familiar with the needs of patients with kidney impairments can help you stay well-nourished and continue to enjoy your food.