By Melissa Pryer, LDN, RD, CNSD

With so many fad diets in today’s mainstream, how is a person to know fact from fiction? Currently, one popular diet approach is the low-carbohydrate diet. Low-carbohydrate diets encourage people to strictly limit carbohydrate foods considered to have a high glycemic index. As defined by The New Glucose Revolution – Complete Guide to Glycemic Index Values, the glycemic index is a physiological measurement of carbohydrate quality. Carbohydrate quality is determined by the immediate effect foods have on blood-glucose levels. A carbohydrate that quickly breaks down during digestion and produces a quick blood-glucose response has a high glycemic index. Carbohydrates that slowly break down and gradually release glucose into the bloodstream are considered to have a low glycemic index.

When following a low-carbohydrate diet, people are encouraged to substitute low glycemic index foods for the high glycemic foods they might typically eat. Some examples of foods with a high glycemic index include sugar, syrups, honey, breads and pastas made with white flour, white rice, carrots, white potatoes, many fruits and fruit juices and many ready-to-eat breakfast cereals.

Foods defined as low-glycemic include meat, fish, poultry, eggs, nuts, most non-starchy vegetables, cheese and fats such as oils, butter and shortening. For a complete list of foods and their glycemic index, please visit www.glycemicindex.com.

Promoters of the low-carbohydrate approach to weight loss believe that by decreasing carbohydrate intake, particularly carbohydrates with a high glycemic index, decreases the presence of glucose in the bloodstream. As a result, the body releases less insulin, a hormone that helps transport glucose from the bloodstream into the cells. The decreased insulin response leads to fewer excess calories converted to fat stores. The safety, efficiency and long-term effects of this diet approach are unknown and continue to be debated by health professionals.

In the article Weight-loss and Nutrition Myths, published by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), many myths about nutrition, weight loss and exercise are discussed. Concerning weight loss, NIDDK discusses the importance of a balanced diet, including foods from all food groups. Following a low-carbohydrate, high protein diet is not considered balanced and may lead to a decreased intake of whole grains, fruits and vegetables, which can cause constipation from low fiber intake. These foods are also good sources of many vitamins and minerals needed by the body. Decreasing intake of these foods may lead to vitamin and mineral deficiencies. Another main concern with this diet approach is a condition known as ketosis. Ketosis is a buildup of partially broken-down fats (ketones) in the bloodstream and may occur if less than 130 grams of carbohydrates are consumed each day. As a result of ketone build-up in the blood, the body may produce high levels of uric acid, which is a risk factor for developing gout and kidney stones. For pregnant women and people with diabetes or kidney disease, ketosis is especially dangerous. 

How does this approach to weight loss impact people with kidney disease? Many individuals with kidney disease follow a diet that restricts intake of certain minerals and fluid. Often, this diet restricts the intake of sodium, potassium, phosphorus, protein and fluid at various degrees based upon the nature and severity of the person’s kidney disease. Monitoring intake of these nutrients can possibly slow disease progression and prolong remaining kidney function.

Because of numerous dietary restrictions necessary for a renal diet, many foods from each food group in the Food Guide Pyramid can only be eaten in small quantities. For example, foods such as canned soups or vegetables, many frozen dinners, luncheon meats, bacon and sausage should be limited due to high sodium content. Intake of tomatoes, potatoes, oranges, bananas, spinach and prune juice should be limited because they are high in potassium. Meat, beans, nuts and most dark cola drinks are high in phosphorus and should be consumed in controlled amounts. High-protein foods such as meat, poultry, fish, cheese and nuts should be eaten in adequate amounts, but not in excess, which can unnecessarily increase the workload of the kidney. Intake of all fluids must be monitored and adjusted based on weight, presence or absence of swelling and urine output. Necessary dietary restrictions will greatly vary based on remaining kidney function and if the person is on hemodialysis or peritoneal dialysis. A renal dietitian can individualize a diet pattern for each person’s needs.

Because so many foods may be restricted in the renal diet, patients may find it difficult to meet calorie and protein needs. By adhering to a low-carbohydrate regimen in conjunction with the renal diet, the challenge to ensure adequate nutrition becomes even greater, if not impossible. When calorie and protein needs are not adequately met, people with chronic kidney disease (CKD) are at increased risk of malnutrition and have a greater susceptibility to other subsequent illnesses.

Strategies and guidelines for weight loss and weight maintenance for those with CKD are similar to those without CKD. Eating more calories than the body can utilize causes weight gain. Weight loss occurs when the body utilizes more calories than consumed. Key components to understanding caloric intake control are keeping food records and understanding portion size. Records enable a person to analyze typical eating patterns and food choices, and then determine what changes need to occur. When keeping a food record, document foods eaten, portion size consumed and when foods are eaten. The food record should reflect three to five days and include weekdays and weekends. The food record will reveal current eating patterns and opportunities for improving diet. A dietitian can analyze the food record and provide a detailed analysis, personalized instruction and individualized recommendations based on findings.

Understanding portion size is another key component for successful weight loss and weight maintenance. Portion sizes can be determined by reading food labels or by using a standardized tool, such as the Food Guide Pyramid. When looking at food labels, the label will indicate the serving size, number of servings and nutrition components (calories, total fat, total carbohydrate, protein, etc.), which are reflective of one serving of that product. The Food Guide Pyramid provides a more generalized approach by defining serving sizes for several food items that fall into different food groups of the Food Guide Pyramid. Regardless of the method utilized, understanding a portion of a particular food, and comparing it to one’s usual intake, allows a person to better control caloric intake and be more successful with weight loss and maintenance.

Many theories and strategies about weight loss are currently circulating in the healthcare industry and media. It is important to understand the basis of each claim and review credible resources discussing each new idea. To promote safe, long-lasting weight loss and weight maintenance, healthcare professionals repeatedly deliver the same message:

“A diet that includes a variety of foods from all food groups in the appropriate portion size accompanied by consistent physical activity is the only proven safe and effective method to reach and maintain a healthy weight.”

Melissa D. Pryer, LDN, RD, CNSD is a clinical dietitian and preceptor of dietetic interns at Touro Infirmary in New Orleans.

Resources:

1. The Food Guide Pyramid – USDA Center for Nutrition Policy and Promotion (www.usda.gov/cnpp/pyrabklt.pdf)

2. How Much Are You Eating? – USDA Center for Nutrition Policy and Promotion (www.usda.gov/cnpp/Pubs/Brochures/index.html)

3. Guidance on How to Understand and Use Nutrition Facts Panel of Food Labels –USDA Center for Food Safety and Applied Nutrition (www.cfsan.fda.gov/~dms/foodlab.html)

4. NIDDK Weight-control Information Network (www.niddk.nih.gov/health/nutrit/nutrit.htm)

The information contained herein is intended for educational purposes only. It is not intended and should not be construed as the delivery of medical care. Persons requiring diagnosis or treatment, or those with specific questions, are urged to contact their local healthcare provider for appropriate care.

This article originally appeared in the December 2004 issue of Kidney Beginnings: The Magazine, Vol. 3, No. 4.

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