Case Study: Man With Type 2 Diabetes and Stage 1 Kidney Disease on Atkins-Like Diet Free

C.S. is a 45-year-old Hispanic man with a 10-year history of type 2 diabetes. He has a glycated hemoglobin of 7.0% and a blood pressure of 130/80 mmHg, treated with an angiotensin-converting enzyme inhibitor for the past 2 years. He has stable background retinopathy and is a nonsmoker. His BMI has been 30 (height 5′10″, weight 210 lb) for the past year. However,lately, he has put himself on the latest high-protein diet (i.e., the Atkins diet).

His weight has dropped by 10 lb, his fasting serum triglyceride level has fallen from 185 to 130 mg/dl, and his blood pressure has decreased to 120/78 mmHg. His LDL cholesterol has remained stable at 102 mg/dl on a statin. His serum creatinine is 0.9 mg/dl, and his 24-hour urine shows a significant increase in microalbumuria from 100 mg/24 hours last year to the current 200 mg/24 hours. He has stage 1 chronic kidney disease indicating kidney damage,with a normal glomerular filtration rate (GFR) of 98 ml/min/1.73 m².

1. Would the weight reduction, blood pressure, and lipid-lowering accomplished by this high-protein, low-carbohydrate diet be an acceptable choice for a patient who is at significant risk of cardiovascular disease?

2. What are the recommendations of the American Heart Association (AHA), the National Kidney Foundation (NKF), the National Academy of Sciences, and the American Diabetes Association (ADA) regarding this type of diet for diabetes and/or weight loss?

3. What has research revealed about appropriate levels of macronutrients for patients such as C.S.?

It is likely that microalbuminuria is the start of a continuum progressing to macroalbuminuria and proteinuria. Microalbuminuria predicts renal disease in diabetes (both type 1 and type 2) and relates to premature mortality. Microalbuminuria is also a marker for pronounced diabetic vascular disease(endothelial dysfunction and chronic low-grade inflammation). Abnormal albuminuria is a major risk factor for cardiovascular complications,predicting increased cardiovascular morbidity and mortality.¹ 

Twenty to thirty percent of patients with type 2 diabetes develop evidence of nephropathy. Some patients already have microalbuminuria or overt nephropathy upon diagnosis. Without intervention, 20-40% of those with microalbuminuria progress to overt nephropathy. For those on the continuum from overt nephropathy to end-stage renal disease (ESRD), the greater risk of death from coronary artery disease (CAD) may intervene.² 

The average adult protein intake in the United States is 15-20% of total calories and has remained consistent from 1909 to the present.³  Most Americans eat 50% more protein than they need. The Recommended Dietary Allowance (RDA) is 0.8 g of good quality protein per kilogram body weight per day for men and women. The high-protein Atkins and Zone diets recommend 125 g/day (36% kcal from protein) and 127 gm/day (34% kcal from protein),respectively.⁴  The initial phases of the South Beach diet are similar, but no specific nutrient intake can be found in the diet's literature. In C.S., the Atkins diet would contribute 1.3 g protein/kg body weight and 36% of total daily calories from protein. Thus, high-protein diets promote a significantly abnormally high protein intake.

There is some evidence that a sustained high-protein diet can adversely affect renal function, especially in people with diabetes with or without mild renal insufficiency. In patients without renal insufficiency, a high-protein diet may act by acutely increasing the GFR and causing intraglomerular hypertension, which may cause progressive loss of renal function. In the Nurses Health Study, 1,624 female nurses between 30 and 55 years of age were followed for a period of > 11 years. The highest quartile of total protein intake, an average of 93 g/day, was significantly associated with a decline in GFR in women with mild renal insufficiency, thus worsening renal disease.⁵  Previous studies had shown mixed results of high-protein diets on renal function but had limitations such as small patient numbers, limited follow-up, and a narrow range of protein intake.

Looking at this relationship from another angle, a meta-analysis recently showed that protein restriction retards the rate of decline in GFR, thus lessening kidney damage. The resulting decrease in kidney damage was small and not impressive. However, when studies looking at people with diabetes were combined, a total of 102 patients given a mean protein restriction of 0.7 g/kg/day versus a control group given 1 g/kg/day (a narrow range), showed a more impressive improvement in renal function independent of the original renal function over 22 months.⁶  A crosssectional study of > 2,600 people with type 1 diabetes found that a protein intake > 20% of calories was associated with an increased urinary albumin excretion rate. Researchers concluded that people with diabetes should not exceed a protein intake of 20% of calories.⁷  Any study in type 1 diabetes is applicable to type 2 diabetes as it relates to nephropathy. Therefore, there is evidence to recommend avoidance of high protein intakes in patients at risk for renal disease, i.e. all patients with type 1 or type 2 diabetes.

Nutrient analysis of high-protein diets is a concern. With some high-protein diets, such as Atkins, come carbohydrate restrictions. Yet high-carbohydrate foods, such as fruits, vegetables, and low-fat dairy products, provide potassium, magnesium, and calcium, which modestly reduce blood pressure.⁸ Normal blood pressure is critically important in preventing CAD and microalbuminuria. With high-protein diets and carbohydrate restrictions come decreased-fiber diets. High-fiber diets have many beneficial effects,including weight loss and lower cardiovascular and cancer risks. With high-protein diets come higher intakes of saturated fats, which are potentially atherogenic.⁹  In addition, experimental evidence indicates that a high-protein diet and the resultant increase in saturated fat intake may accelerate the progression of renal disease. Increased LDL cholesterol can stimulate mesangial hypertrophy and stimulate cytokine formation, which may ultimately cause tissue injury. In both type 1 and type 2 diabetes, hypercholesterolemia is a predictor of deteriorating kidney function.¹⁰ 

The RDA for carbohydrate is set at 130 g carbohydrate/day for adults and children based on the average minimum amount of glucose utilized by the brain to ensure optimal brain function.¹¹  That pretty much omits Atkins (28-33 g/day) and the early phases of the South Beach diet. Recent AHA guidelines discourage high-protein diets for weight loss,citing potential increased risk for coronary heart disease and renal disease.¹²  The most recent ADA technical review on nutrition states that high-protein diets are not recommended until further research establishes their safety.³  Concerns include renal function and cardiovascular disease. The NKF states in its Kidney Disease Outcomes Quality Initiative guidelines for chronic kidney disease that there is no benefit from a protein intake higher than the RDA of 0.8 g/kg body weight and that this is a reasonable level to recommend for patients with chronic kidney disease in stages 1-3.¹³  Thus, many respected nonprofit health care organizations discourage the use of high-protein, low-carbohydrate diets.

Literature reviews of research on the effect of high-protein,low-carbohydrate diets on obesity and lipid levels are not convincing. A review of the literature describing adult outpatient recipients of low-carbohydrate, high-protein diets compared a wide variety of study designs,carbohydrate levels, durations, and calorie levels. Only five studies evaluated low-carbohydrate, high-protein diets for > 90 days, and these were nonrandomized, uncontrolled studies. The three variables that most predicted weight loss were calorie level, duration of calorie restriction, and number of very obese participants in the study. Reduced carbohydrate content was not significantly associated with weight loss.¹⁴ 

Another review concluded that populations at risk for renal disease, such as patients with diabetes, should avoid high-protein diets. The authors also caution that evidence suggested that protein intakes in excess of two to three times the RDA may have harmful effects on calcium homeostasis and possibly bone mass,¹⁵  a problem for a population already predisposed to osteoporosis. In addition, a comparison of high-protein, low-carbohydrate diets versus a low-fat diet for weight loss shows them equally effective after 1 year in duration.¹⁶  A recent small, randomized, clinical trial comparing a low-carbohydrate (< 30 g) to a conventional low-fat diet in severely obese patients, including individuals with diabetes, showed no significant difference in weight loss after 1 year, although weight loss was minimal (11 vs. 7 lb). Of interest was that the weight loss on the low-carbohydrate diet did not appear to be sustainable and that blood urea nitrogen levels increased more in the low-carbohydrate group.¹⁷ 

Reduced energy intake is an important therapeutic objective for the patient in the case described above. Reduced energy intake would reduce his blood pressure and serum lipids as well as improve his glycemic control. Weight loss was effective in lowering his blood pressure and serum triglycerides, as one would expect. However, the macronutrient content of his diet may have exacerbated the microalbuminuria. Therefore, a patient such as C.S. would be illadvised to stay on the high-protein diet because of the potential risk to his kidney function as shown by his elevated microalbuminuria.

With guidance from a registered dietitian, C.S. started a 1,500-kcal,low-fat diet with a walking program of 2 miles/day, 6 days/week. He was very tired of the restrictive nature of the high-protein diet and welcomed a change. His urine microalbumin level fell to < 50 mg/24 hours.

Two important studies show strategies that work to yield long-term weight loss. In order to determine what strategies work for long-term weight loss,the National Weight Control Registry elicited and studied information from> 800 people who have been successful in this endeavor. Only half had lost weight through weight loss programs. The remainder had lost weight without medical intervention. Keys to success were an average calorie intake of ∼1,400 kcal/day, a low-fat diet (24% of kcal), and a high energy expenditure through exercise (2,800 kcal/week).¹⁸  The Diabetes Prevention Program also documented that a low-fat diet, increased physical activity, and educational sessions with frequent follow-up allowed participants to lose 7% of their body weight and maintain a 5% weight loss for 3 years.¹⁹ 

• High protein intakes cause higher workloads for kidneys, whose function is to handle amino acid fragments during protein degradation and excrete nitrogen as urea.

• There is no research documenting that a high-protein diet maintains weight reduction any better than a low-fat diet, which is safer and offers long-term results.

• Safety and efficacy of high-protein, low-carbohydrate diets are a concern for patients with diabetes, regardless of documented kidney disease.