Possibility of kidney stones and bone loss - Weight Control - low-carbohydrate, high-protein diets - Brief Article - Statistical Data Included

USA Today (Society for the Advancement of Education), Oct, 2002

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 diet. Subject readings improved to 581 mg per day during intake of the moderately carbohydrate-restricted diet. Net acid excretion rose from baseline levels of 61 milliequivalents per day to 116 during the severely carbohydrate-restricted diet phase. Chronic acid load suppresses the function of osteoblasts (bone -forming cells) and stimulates the function of osteoclasts (a cell associated with bone resorption).

Wang explains that "This type of diet increases the propensity to develop kidney stones. On the basis of this study alone, there was an increased risk of developing kidney stones and a possible increase in the risk of bone loss. We already know that osteoporosis is going to be a major issue as the population ages and, if people are going to eat this kind of diet on a long-term basis, it's unknown what the implications would be for your bones."

"We are not questioning the value of this diet in producing weight loss," stresses Kashayer Sakhaee, coauthor of the study and a professor of internal medicine. "We are investigating a countermeasure so that subjects can benefit from weight loss without experiencing the side effects of increased risk of [kidney] stones and bone loss."