NN&I - July 2010
22 Nephrology News & Issues July 2010www.nephronline.comNutrition Update salts, it is important to understand the difference between organic and inor -ganic phosphorus. Phosphorus found naturally in foods is termed organ -ic because it is bound to phytates. Phosphorus in phytates (or phytic acid) is bound to inositol in the fiber of raw whole grains, legumes, seeds, soybeans, and nuts. Humans lack the enzyme phatase, necessary for releas-ing the phosphorus from the phytates during digestion and therefore are unable to absorb phosphorus-phytate. Mammals absorb approximately 50% of phosphorus from plant sources and 70% of phosphorus from animal sources. In contrast, phosphorus added during food processing is mostly in the form of inorganic salts and is almost completely absorbed. Thus, inorganic phosphorus represents an even larger phosphorus burden than ingesting a similar amount of organic phosphorus.4Another challenge is that it is cur -rently impossible to accurately calcu -late the amount of inorganic phospho -rus found in foods.5 Most of the soft -ware programs available to estimate a patient's phosphorus intake are based on standard food composition tables, which usually do not include the phosphorus from these additives. This leads to an underestimation of dietary phosphorus intake. Food label-ing regulations in the United States do not require manufacturers to list the phosphorus content in the "Nutrition Facts" panel of food as they do for sodium.6Is chicken good or bad for you? Chicken is a prime example of the problem. When 38 different chicken products were analyzed for inorganic phosphorus additives, 35 (92%) had phosphorus-containing additives list -ed among their ingredients.6 Sullivan et al. found an average of 440 mg of phosphorus in two 100 g servings of additive-containing products. The actual phosphorus content was great -er than the content expected from nutrient database for every category of chicken products containing addi -tives. For example, actual phospho- rus content exceeded expected phos-phorus content by an average of 84 mg/100 g for breaded chicken breast strips.7 Variation exists within cate -gories as well. For example, the dif- ference between actual and expected phosphorus content ranged from 59 to 165 mg/100 g for breast patties. An analysis examining the potassi -um and phosphate content in a variety of 'enhanced' and additive-free meat and poultry products available in local supermarkets found that prod-ucts that were labeled enhanced had an average phosphate concentration 28% higher than additive-free prod-ucts, with some products almost 100% higher.1What's best for patients? So, with this in mind, should we still be restricting such healthy and economic foods, such as beans, whole wheat bread, dairy and peanut butter, and directing our patients to consume enhanced chicken meals? A research study published in the Journal of the American Medical Association con -cluded, "Educating end-stage renal disease patients to avoid phospho-rus-containing food additives resulted in modest improvements in hyper -phosphatemia."2 Since educating our patients promotes little improve -ment in their meal selection, perhaps offering healthy, appealing, previous -ly banned alternatives may improve their diets and clinical outcomes. The foods eaten alongside of phos-phorus-containing foods can also affect phosphorus absorption. The yeast in certain bread and live cultures (often termed probiotics) in yogurt enhance the digestibility and absorp -tion of phosphate. For example, eating peanut butter with yeast-containing bread or oatmeal with yeast-contain -ing toast will enhance phosphorus absorption.8 This makes quantifying the actual phosphorus absorbed very difficult since we tend to eat a mixed diet rather that a single food in isola-tion. However, as dietitians we spend Dietary advice made easy... or not Patient: What beverages can I drink? Dietitian: Home-made iced tea is fine, as are Arizona and Turkey Hill, but Nestea Cool, Lipton Green Tea, or Snapple Green Tea should not be part of the kid-ney diet. Water and Dasani flavored water are fine, but Aquafina flavored water, Vitamin water, or Propel water are not appropriate for the kidney diet. Patient: What about chicken. Can I eat that? Dietitian: Most chicken is fine as long as it is additive free from the grocery store. Stay away from additive added fast food chicken as well as additive added chicken in frozen meals. Patient: What about breads? Dietitian: Become familiar with the leavening agents in the breads you want to eat. If they use baking powder such as biscuits and corn breads then that is not advisable. Breads using yeast are also not recommended because it enhances the phosphorus absorption. Best selections are unleavened breads such as pita, tortillas, naan or matza breads. Patient: Thank you, I think. Nutrition Update_NNI0710_7.indd 22 6/16/10 2:59:07 PM
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