The Low Protein Diet Versus Other Diets

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Carmelo Giordano and Sergio Giovannetti in Italy first reported on the use of very-low-protein diets supplemented by essential amino acids in chronic renal failure 40 years ago. Although their clinical results were impressive, their diets, which contained very small amounts of protein, were almost intolerable. Jonas Bergström and his associates in Sweden were the first to recommend what I am now referring to as the very-low-protein diet. This diet contains about 22 g per day of protein for an average-size individual, much less than the average U.S. intake of about 100 g per day of protein. The reason this very low intake of protein is acceptable to most patients is that the sources of dietary protein are not restricted; any food that stays within these limits is acceptable. This feature is critical, and is possible with the addition to the diet of supplements containing all of the essential amino acids as such or as their biochemical equivalents. Hence there is no need to be concerned about the amino acid composition of the foods consumed. This supplementation removes the threat of protein malnutrition, which has been the main argument against protein restriction.

In contrast, an unsupplemented low-protein diet, such as the 40 g protein diet that some nephrologists recommend (with the caveat that it may cause protein malnutrition) must emphasize so-called high-quality proteins, those proteins that contain very specific proportions of the essential amino acids. This requirement limits the variety of foods that can be included in the diet.

Another reason the very-low-protein diet is tolerated better than you might expect is because high-protein foods, such as meat and poultry, usually are totally excluded. For most patients (but not all), this is easier to adhere to than a diet that permits the occasional chicken or beef dish.

One reason these low-protein diets improve the signs and symptoms of renal failure is that they enable the body to utilize the nitrogen content of food more efficiently. You need less nitrogen in your diet to maintain your body's protein stores. Since intake of nitrogen seems to cause many of the signs and symptoms of kidney failure, less nitrogen makes people feel better.

If such diets slow the progression of kidney failure (which has not been firmly established, but is at least a possibility, as illustrated by a number of poorly controlled reports and by the case histories in Chapter 22), the mechanism by which they do so is unknown. One conceivable possibility is reduced cortisol production due to protein restriction; cortisol may play a role in disease progression.

One would suppose that a 40 g protein diet would be easier to follow than the one we recommend, but, in fact, the opposite is more often the case. In a study from Germany, patients reported a preference for the very-low-protein diet with supplements. A major difference, as explained earlier, is that there are no restrictions as to which foods are allowed, as long as they are low in protein.

In a random nine-month study, researchers compared a low-protein diet, limited to "high quality" proteins (the "potato-egg diet") with a diet containing 15 to 20 g of protein per day supplemented by essential amino acids. In patients on the supplemented diet, anemia was less severe, serum phosphorus levels were lower, and serum levels of several proteins were higher. The very-low-protein diet was thus more efficacious as well as easier to follow.

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