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Ask the Medical Expert Archives 2000-2004

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Low Carb Dieting
May 2000

Q. Can you tell me if increased protein intake and decreased carbohydrate intake is a well-founded diet plan? It seems that American culture dictates a very high carbohydrate intake, and we are in the worst shape of any nation. Also, is there any relationship between this and the formation of kidney stones?

A. A fairly reasonable approach is to have a majority of your calories come from carbohydrates with less coming from protein and fat. One common ratio is 40:30:30 (40% of the calories from carbohydrates, 30% protein, and 30% from fat). While at first this may seem strange, it does make a lot of sense. The American diet has far more protein than it needs, and often times protein foods are fatty foods (for example a steak is high in protein and high in fat). So by limiting your intake of protein, you can coincidentally decrease your intake of fat, which is always considered a good idea. In addition, the vast majority of amino acids (the building blocks for protein) can be made by the body from carbohydrates.

There is a trick to the 40:30:30 ratio. Each gram of protein and each gram of carbohydrate have about four calories, whereas each gram of fat has about 9 calories. So while the above ratio indicates that the amount of protein and fat that you consume should be about equal, this is on a calorie-to-calorie basis. Since fat has twice the calories per gram that protein does, one would have to eat half as much fat as protein for the above ratio to hold. As an example, given a 2,000 calorie per day diet the 40:30:30 ratio suggests that you would get 800 calories from carbohydrate, 600 calories from protein and 600 calories from fat (800 + 600 + 600 = 2,000). Given the above numbers, this means 200 grams of carbohydrate, 150 grams of protein and about 55 grams of fat.

Clearly these numbers are just ballpark suggestions, but they do lead one to a more healthy diet. The question about the kidney stone is interesting, because a high protein diet can foster the promotion of certain types of kidney stones.

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