Slim Pickings: The Facts About Low Carbohydrate,
High Protein Diets

Pamela S. Kent

Obesity is a chronic disease that has become a major health problem in most industrialized countries because of its high prevalence, causal relationship with serious medical illnesses, and economic impact. According to the third National Health and Nutrition Examination Survey (NHANES III), the prevalence of obesity (defined as a body mass index, BMI greater than 30) increased 8.4% over the past decade and it is estimated that more the one-third or 97 million people in the United States between the ages of 20 and 70 are obese (Coresh, Astor, Greene, Eknoyan, & Levey, 2003). This increase in obesity has intensified the search for an effective weight loss strategy.

Addressing the Obesity Epidemic

Historically, protein energy malnutrition (PEM) has been the main nutritional concern in the CKD population, not “overnutrition.” In the past 20 years, the obesity epidemic and the incidence of end stage renal disease (ESRD) have risen considerably in the United States. According to the USRDS (2005) there are 430,000 individuals requiring renal replacement therapy. Approximately 20 million individuals have mild to advanced CKD and 8 million of those have less than 60% of kidney function remaining. Since obesity is predominantly associated with type 2 diabetes and systemic hypertension, the primary causes of ESRD, one can speculate that obesity may be one of the most frequent precursors of ESRD (Hall et al., 2004; Reisin, 2001).

Should patients who are obese with renal impairment be encouraged to reduce their weight? There are currently no guidelines for weight loss management in patients with CKD. Weight reduction can be an important adjunct to both blood pressure and glycemic control (Moloney, 2000). Weight reduction in patients who are obese into the high end of normal BMI range may also help to reduce the high cardiovascular mortality and morbidity of patients with uremia. The initial goal of weight loss initiatives should be to reduce body weight by approximately 10% from baseline in accordance with the National Heart, Lung, and Blood Institute (NHLBI) guidelines.

Tailoring the Weight Loss Diet

Some weight loss diets are nutritionally sound and consist of recommendations for healthy eating while other popular diets may cause metabolic complications (Freedman & Kennedy, 2001). Low carbohydrate, high protein diets greater than 1.5 g protein/kg BW are commonly used for weight reduction in the general population. Although these diets may pose no risk to the healthy population in the short term, there is no long-term evidence to support overall efficacy and safety (Einenstein, Roberts, Dallas, & Saltzman, 2002). Due to rising incidence and prevalence of the overweight population and the susceptibility to CKD, high protein diets pose a significant risk to this population. Any patient considering following a high protein diet should preferably have their glomerular filtration rate (GFR) checked as a serum creatinine level may be misleading (Friedman, 2004).

The protein recommendations of the low carbohydrate, high protein diets far exceed the recommended protein intake for both the general and CKD population as shown in Table 1. There are a number of reasons to suspect that these diets may cause metabolic alterations in renal function (Friedman, 2004; Reddy, Wang, Sakhaee, Brinkley, & Pak, 2002). Individuals with diabetes can accelerate preexisting renal disease with a high protein intake. Typically the protein is from animal sources that increase total fat, saturated fat, and cholesterol intake. High protein foods also contain purines that are metabolized to uric acid and may cause gout. Excessive protein intake also increases urinary calcium loss, which could lead to osteoporosis as well as increasing the GFR that causes hyperfiltration and glomerular injury. There is also a risk for microalbuminemia in individuals with diabetes and hypertension who ingest high protein intakes. In addition, the elimination of beneficial carbohydrates like whole grains and vegetables may increase the risk of cancer. The resulting ketosis from a deficit of carbohydrates could impact fluid and electrolyte homeostasis. There is also concern that high protein diets may be associated with kidney stones (Reddy et al., 2002). Therefore, patients with a GFR less than 60 ml/min/1.73 m2 or diagnosed with nephrotic syndrome should avoid a high protein diet.

The weight loss diet for the kidney patient should be tailored to the needs of the patient and should be adequate nutritionally. The essential components of a weight management program should include a calorie reduction of 300-500 calories per day, appropriate variety in food choices and reduction of fat to no more than 30% of daily calories. The safety and efficacy of weight loss in overweight individuals requiring renal replacement therapy is unknown. The 2005 Clinical Practice Guidelines for Cardiovascular Disease in Dialysis Patients (National Kidney Foundation, 2005) suggest that weight loss in the dialysis setting should be closely monitored by a registered dietitian and physician.

Conclusion

Strategies to address the epidemic of obesity must encompass a wide range of behavioral, social, and environmental factors. If weight loss is to be successful, an interdisciplinary team approach should be employed. The goals for obesity treatment are to decrease body weight, prevent relapse, and develop supportive eating and physical activity behaviors. Appropriate renal diet modifications should be recommended according to the stage of CKD. Studies are still needed to assess intentional weight loss strategies in the CKD patient.

References
Coresh, J., Astor, B.C., Greene, T., Eknoyan, G., & Levey, A.S. (2003). Prevalence of chronic kidney disease and decreased kidney function in the adult U.S. population: Third National Health and Nutrition Examination Survey. American Journal of Kidney Diseases, 41(1), 1-12.

Einenstein, J., Roberts, S.B., Dallas, G., & Saltzman, E. (2002). High-protein weight-loss diets: Are they safe and do they work? A review of the experimental and epidemiologic data. Nutrition Reviews, 60, 189-200.

Freedman, M.R., & Kennedy, E. (2001). Popular diets: A scientific review. Obesity Research 9(1), 1S-40S.

Friedman, A.N. (2004). High-protein diets: Potential effects of the kidney in renal health and disease. American Journal of Kidney Diseases, 44(6), 950-962.

Hall, J.E., Henegar, J.R., Dwyer, T.M., Liu, J., Da Silva, A.A., Kuo, J.J., et al. (2004). Is obesity a major cause of chronic kidney disease? Advances in Renal Replacement Therapy, 11(1), 41-54.

National Kidney Foundation. (2005). K/DOQI clinical practice guidelines for cardiovascular disease in dialysis patients. American Journal of Kidney Diseases, 45(supp. 3), S1-S154.

Moloney, M. (2000). Dietary treatments of obesity. Proceedings Nutritional Society, 59(4), 601-608. Retrieved February 25, 2006, from http://www.nhlbi.nih.gov/guidelines/obesity/ e_txtbk/txgd/algorthm/algotext.htm

Reddy, S.T., Wang, C.Y., Sakhaee, K., Brinkley, L., & Pak, C. (2002). Effect of low carbohydrate high-protein diets on acid-base balance, stone forming propensity, and calcium metabolism. American Journal of Kidney Diseases, 40(2), 265-274.

Reisin, E. (2001). Obesity and the kidney connection. American Journal of Kidney Diseases, 38, 1129-1134. Retrieved February 25, 2006, from http://www.usrds.org/adr.htm

United States Renal Data System (USRDS). (2005). USRDS annual data report. Bethesda, MD: National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases.