Increased REE May Make Regaining Weight More Difficult For AN Patients

Patients with anorexia nervosa who have difficulty gaining weight during refeeding may be cooperating fully but may be thwarted by an underlying increase in resting energy expenditure (REE), according to the results of a recent study. French researchers have identified four factors that may make it more difficult for these patients to regain weight despite carefully designed refeeding protocols (Am J Clin Nutr 2004; 80:1469).

In this study of 87 malnourished women with anorexia nervosa (mean body mass index, or BMI: 13.2 kg/m2), refeeding induced an increase in REE; this remained higher than baseline when free fat mass (FFM) was taken into account. Dr. Virginie Van Wymelbeke and co-workers at Le Bocage University Hospital, Dijon, France, identified anxiety, abdominal pain, physical activity and cigarette smoking as factors that interfered with their patients’ weight gain.

The 87 anorexic women were hospitalized for nasogastric tube feeding for about 2 months. The authors measured oral food intake plus enteral nutrition, body weight and body composition, body temperature, REE, physical activity, mood, abdominal pain, cigarette smoking, nutritional status, serum thyroid-stimulating hormone and other thyroid hormones, and catecholamines. Each variable was measured before refeeding, upon “spontaneous” oral intake while the patient was in the hospital and after 8, 30, and 45 days of refeeding. Before refeeding, the free triiodothyronine (T3) concentration was low in 78 of 87 patients (89%), whereas free thyroxine (T4) and TSH were within normal levels.

Recovery was defined as a stable and normal body mass index above 18 kg/m2 and normal energy intake (1.5 x REE), and disappearance of fear of eating and fear of becoming fat. A final criterion for recovery was normal eating behavior at the one-year follow-up visit. The 87 patients were compared with 48 healthy non-anorexic women of the same age (mean BMI: 21).

Four factors and the need for more food during refeeding

After one week of refeeding, body temperature increased significantly and oral intake plus enteral feeding reached a mean of 2.5 times the initial intake. There was a significant increase in body weight (an increase of a mean of 3.28%) and the mean REE:FFM ratio increased significantly (11.7%). The increase in REE:FFM was reported in 78 of the 87 patients. The authors noted that the rise in REE observed at the beginning of refeeding could not be explained by FFM alone. In fact, there was no increase in either FFM or muscle mass. In addition, the one-week increase in REE represented 31% of the total REE increase during the 2.5 months of refeeding. These data suggest that during overfeeding the metabolic rate of FFM cells increases within a few days.

The second factor linked to the increase in REE:FFM is anxiety, which could be due to the patient’s fear of gaining weight—this mechanism seems to be present throughout refeeding. This was clearly suggested by the positive correlation that was found between anxiety level and REE:FFM in patients who had a poor outcome after discharge. The third factor, depression, may contribute to lower REE. Levels of physical activity and abdominal pain are another pair of potential factors. Physical hyperactivity is one method that patients with anorexia nervosa use to try to lose weight. Finally, the authors found an interaction between REE:FFM and smoking status: nonsmokers and light smokers tended to have an REE:FFM l4% lower than that in the two other groups, who were heavier smokers.

Eighteen of the patients recovered, but 15 had a poor outcome, which was defined as a loss of 7.2 kg and a mean BMI of 15.5 at the end of the study. The authors estimated that these patients lost a mean of 7 kcal/day per gram of body weight due to increased REE. They also note that a body weight gain of 150 gm/day requires an additional 2600 kcal/day, or 75 kcal/kg body weight/day, to achieve a steady weight gain. They suggest that, once the risk has been identified during refeeding in the hospital, patients be given 1.4 X REE plus about 7 kcal/gm body weight/day to achieve desired weight gain.