Possibility of kidney stones and bone loss.

• Position: Weight Control - Low-carbohydrate, high-protein diets - Brief Article - Statistical Data Included

Popular low-carbohydrate, high-protein diets may result in rapid weight loss, but researchers at the University of Texas Southwestern Medical Center at Dallas report that they also pose serious health problems, including an added susceptibility to kidney stones and a possible greater risk of bone loss. They note that acid excretion--a marker for the acid load in the blood--increases as much as 90% while subjects are on diets that severely restrict carbohydrates. Levels of urinary citrate, which inhibits kidney stones, fell by almost 25% in the group during a six-week study.

When you restrict the amount of carbohydrates, you can go into a state called ketoacidosis," Chia-Ying Wang, assistant professor of internal medicine, points out. "Our body needs a certain source of energy and a quick source are carbohydrates, which are readily available. When you restrict carbohydrates, the body then turns to other sources, one of which is fat. Ketone bodies are formed when the body is forced to burn fat for energy."

Ten healthy subjects ate a regular diet for two weeks at the start of the study. They followed that with a highly restrictive one that included some vegetables, but no fruits, and fewer than 20 grams of carbohydrates per day for two weeks. Participants then ate a less-restrictive diet for the final four weeks. Urinary citrate levels fell from 763 milligrams per day to 449 during intake of the severely carbohydrate-restricted...