Determining Energy Needs for Patients with Eating Disorders

“Eat when you are hungry and stop when you are full” is an expression I wish I could use with clients. After all, this is how many individuals meet their daily energy needs. But, for most clients with eating disorders, this mantra is not appropriate. For one thing, patients typically do not experience accurate hunger and fullness cues in the early stages of their nutritional recovery. Secondly, even if they do have accurate internal cues, they usually struggle with the ability to give themselves permission to eat. That is the nature of an eating disorder.

A Need for Structure

Generally, patients need a considerable amount of structure when normalizing their eating pattern during recovery. They require guidance about when, what, and how much to eat because the eating disorder has distorted their perception of normal, healthy eating behavior.

Mechanical eating and meal plans are two tools dietitians use to get patients back on track. Mechanical eating determines when the patient should have meals and snacks by suggesting she eat every three to four hours. Meal plans, which are designed with the client’s input, determine the content of meals and snacks in terms of the food groups and recommended number of servings.

Determining Energy Needs

Unlike the internal cue approach to eating, however, meal plans entail providing clients with a specific caloric prescription. Dietitians determine the amount of food energy necessary to improve the client’s nutritional status and restore their weight, but not make them vulnerable to refeeding complications. The assessment of energy needs in this population can be challenging because many questions remain unanswered regarding the effects of an eating disorder on energy expenditure.

In the May 2002 edition of the International Journal of Eating Disorders, authors de Zwaan, Aslam, and Mitchell summarized what we currently know about this topic. De Zwaan and her colleagues reviewed the available literature concerning the energy expenditure of individuals with anorexia nervosa, bulimia nervosa, and binge eating disorder (In J Eat Dis 2002; 31:361). While the majority of studies measured resting energy expenditure (REE), several measured total energy expenditure using the doubly-labeled water method in both anorexia nervosa and bulimia. A few studies looked at components of total energy expenditure in anorexia nervosa, specifically, dietary induced thermogenesis and activity-induced thermogenesis. It is important to note that REE is the amount of energy used when the body is at complete rest (but the client is not asleep), not controlling for the level of stress and body temperature. REE is one of four components of total energy expenditure.

What the Studies Showed

The authors discovered that the data regarding the impact of binge-eating and purging behavior on REE are inconsistent. To date, it is still not clear whether clients with bulimia nervosa experience the energy-conserving metabolic adaptations that are characteristic of semi-starvation. But for individuals with anorexia nervosa, this is well known. In fact, the most consistent finding noted by the reviewers is a marked reduction in REE when anorexic patients are initially seen at a low weight. Energy expenditure increases rapidly, however, as they progress with refeeding. In other words, in the short term, changes in energy intake are more important than body weight per se in determining energy expenditure for patients with anorexia nervosa.

The authors report that REE is measured most often in clinical settings because it can be done relatively simply using indirect calorimetry. This procedure measures an individual’s consumption of oxygen and production of carbon dioxide using either a respiratory chamber or a ventilated hood. Unfortunately, indirect calorimetry is not an option for most clinicians because of the high cost of the equipment. Instead, they may use predictive equations to estimate the resting energy expenditure of their patients. However, de Zwaan and her team advise clinicians to be cautious about using predictive equations to calculate REE for low-weight patients. Formulas such as the Harris-Benedict Equation or even equations that have been derived specifically for female patients with anorexia nervosa may yield inaccurate estimates of REE.

De Zwaan and her colleagues concluded their review article by recommending that more research be devoted to the subject. They also suggest that future research efforts be designed to further study energy expenditure of individuals with bulimia nervosa and binge eating disorder. As well, the authors believe that future research could lead to reliable and cost-effective ways of measuring REE for patients with anorexia nervosa. Accurate predictions of the energy intake necessary to promote weight restoration for these clients would be clinically useful.

Impact on Clinical Practice

While many in the eating disorders treatment community may not completely understand the effects of an eating disorder on energy expenditure, this review article can give clinicians some reassurance. Several of the observations made by de Zwaan and associates support current treatment practices. Dietitians in this field are already predicting energy levels that achieve weight goals for patients without putting them at risk of refeeding complications.

Most dietitians have their own method of determining the energy needs of their patients. These methods tend not to rely on predictive equations or indirect calorimetry, but on lessons learned from their clinical experience, making it more of an art than a science.

A colleague, Jadine Cairns, a master’s candidate and dietitian with the British Columbia Children’s Hospital Eating Disorders Program, recently shared her method of determining energy needs. Cairns reports that she does not use a predictive equation. In the past, she has tried a formula published in 1995 by Schebendach and associates (Int J Eat Disord 1995;17:59) but found the equation estimated energy needs that she felt were too high for her patients.

Cairns’ approach begins with determining the patient’s current daily energy intake. For patients who are considered at low risk of refeeding syndrome, their current food intake determines the caloric content of their initial meal plan. However, she designs the initial meal plan with at least 1200 kcal/day. Typically, patients begin treatment with caloric prescriptions that range from 1200 to 1800 kcal/day. Clients who struggle with bulimia nervosa and are somewhat close to a healthy weight are prescribed at least 1600 to 1800 kcal/day even if they report eating very little. To promote weight gain, Cairns adds 350 to 500 kcal until the client’s weight goal is reached. For patients considered at a high risk of refeeding complications, she designs the initial meal plan with a caloric prescription of about 800 kcal/day until their serum values for electrolytes, magnesium, and phosphorus are within normal ranges.

— Linda M. Watts, MA, RD