March 2003

Vol. 2     No. 3  

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Restrict Protein – Save Your Kidneys1

The popularity of high protein diets (like Atkins, Zone, Sugar Busters, Suzanne Somers, etc.) and the common use of protein supplements, especially among body builders, are increasing the risk of life-threatening kidney failure for millions of people.  Although the damage caused by excess dietary protein has been recognized for more than 100 years, most people believe this nutrient is the most important one to seek in their diet.  Certainly you need to get enough protein from your foods.  However, the truth is, it is virtually impossible to fail to do so with any diet of natural unprocessed foods – even when these foods are all vegetarian.  The problem is always with getting too much protein – and the consequences of failing to understand this fact, solidly based in science, can mean a miserable life tied to a dialysis machine and a premature death from uremia (the build up of toxic byproducts of metabolism).

Kidneys Filter Out Protein

Your two kidneys are two vital organs located in your abdomen.  They filter the blood, removing excess water, nutrients and impurities from your body.  The protein you eat, that your body does not use, must be eliminated (there is no storage depot in the body for excess dietary protein).  This excess is filtered from the blood by the kidneys and put into the urine for elimination.  You can actually observe the effects of eating too much protein when you see the formation of frothy bubbles in the toilet bowl after urinating following a single high protein meal.  You can also smell the asparagine amino acid from protein found in high concentration in asparagus when you urinate.

As you consume more protein, the kidneys must increase their filtration rate.  Higher filtration rates (called the Glomerular Filtration Rate – GFR) result in higher pressures and flows in the kidneys’ filtration system (nephrons).  This high pressure in medical terms is called intraglomerular hypertension.  This hypertension over long periods of time permanently damages the kidneys’ tissues – and kidney function is lost.

Damage for All – Disease for Some

For most people this damage is inconsequential because their kidneys have such an overabundance of reserve capacity. Two-thirds of kidney function must be lost before illness even begins.  Estimates are that the average American loses only about one-third of his or her kidney function after 70 years of eating the amount of excess protein in the typical American diet – nothing is noticed.  However, this is a different story for someone who already has lost kidney tissue from another cause – such as donating one kidney (half of function is lost) or losing a kidney from an accident.  People with diabetes, hypertension, atherosclerosis, and nephritis – all conditions caused by the American diet – lose kidney function as well.  In these cases, the excess protein typically consumed with the American diet can be deadly.  Even worse, high protein diets commonly used to lose weight (temporarily) and protein powders to build muscle, can be expected to put many more people at risk for failing kidneys. (High protein diets and protein powders really don’t build muscle – if the excess protein we ate went into our muscles, then all Americans would look like Arnold Schwarzenegger.)

Eat the Right Amount of Protein – A Natural Design

The diet I recommend is centered on starchy vegetables, like rice, corn, potatoes, sweet potatoes, breads, and pastas.  The protein content of these foods is ideal as designed by nature through eons of evolution – about 6% to 14% of the calories.  Another advantage of the foods I recommend is they are made of vegetable proteins which are much less troublesome for the kidneys to process than are proteins derived from animal foods.  There are some higher-protein, starchy vegetable foods classified as legumes (beans, peas, and lentils) – these are about 28% protein.  In general, I recommend that a healthy person limit these to, on average, one cup of cooked legumes a day (for example, one day you may have three cups and none for the next two days).  People with loss of kidney function must restrict these legumes even more.  Most green and yellow vegetables are high in protein, but the absolute amount of protein consumed from these low calorie foods is so small that the proteins in these vegetables are rarely of any consequence.  Fruits are low in protein.

As I mentioned, the most burdensome foods for the kidneys are animal products, because they are loaded with protein.  Interestingly, those animal foods lowest in fat are highest in protein.  So, often-recommended white fish, turkey, chicken and skim milk products are going to provide more damaging protein than the higher fat versions of these meats and dairy products.

Understanding the truth about protein will not only protect you from kidney damage, but also osteoporosis.  Plus, the high protein foods your friends are dying for are also loaded with fat and cholesterol leading to heart disease and cancer.  The well-informed consumer will understand that Nature designed her plant foods to be complete and well balanced long before they arrived on the dinner table for your enjoyment.

1) Knight EL.  The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency.  Ann Intern Med. 2003 Mar 18;138(6):460-7.

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