Carbohydrate Oxidation Rates in Patients With Anorexia Nervosa

This study was prompted by the authors' observation that some patients with anorexia nervosa (AN) do not gain weight despite appropriate caloric intake and some recent evidence ¹ that patients with AN respond differently to caloric supplementation depending on what their body habitus was before developing AN. The primary purpose of this study was to study carbohydrate oxidation rates in patients with AN and determine whether differences could be discerned between those patients who gained weight and those who failed to gain weight.

The study consisted of 21 female AN patients whose average weight was 30.1% ± 1.5% below their ideal body weight and 10-age matched healthy women serving as controls (NC). Caloric intake was stabilized over a 10-day period. At the conclusion of the 10-day period, those 21 AN patients were divided into two groups (AN-a consisted of 10 patients who gained less than 2% of their body weight, and AN-b consisted of 11 patients who gained more than 2% of their body weight during the 10-day feeding period). The average daily caloric intakes in the AN-a, AN-b, and NC groups were 1465 kcal/d (42.2 kcal/kg), 2121 kcal/d (58.6 kcal/kg), and 1755 kcal/d (35.2 kcal/kg), respectively. At the beginning of the 10-day study period, after an overnight fast, the subjects ingested 50 g of glucose at 8 AM. Venous blood was sampled for glucose and insulin over the next 3 hours and oxygen consumption and carbon dioxide production were measured with a metabolic cart. Urine was collected for measurement of urinary nitrogen content.

There was no difference in nonprotein respiratory quotient (NPRQ) between AN-a and NC groups. However, NPRQ was significantly elevated in the AN-b group before and after glucose ingestion compared with the NC and AN-a groups. Before glucose ingestion, carbohydrate oxidation rates were 61 6 13 mg/min in the NC group, 55 6 12 mg/min in the AN-a group, and 122 6 13 mg/min in the AN-b group. After glucose ingestion, the rates increased in the NC and AN-a groups and remained elevated in the AN-b group. The plasma glucose response was similar in all three groups, whereas the plasma insulin response was decreased in the AN-b group and tended to be decreased in AN-a group compared with the NC group.

These authors concluded that measurement of the basal NPRQ may be a predictor of weight gain in patients with AN and they go on to suggest that caloric intake may need to be increased in those patients who fall into the AN-a category. They also suggest that hepatic glucose processing enzymes (eg, glucokinase and phosphofructokinase) are present in larger amounts in the AN-b vs the AN-a group; however, the relationship to weight gain is unclear.