Edited by Lisa Ranzenhofer, PhD, and Janet Schebendach, PhD.
As members of the research team at the Columbia Center for Eating Disorders, we are prepared for a variety of questions from those considering a stay at our inpatient treatment program. Among the common questions from patients is, “Why do I have to eat so much to maintain my weight?” And, “How long do I have to do this for?”
While the average daily caloric intake required for a typical adult to maintain their weight is in the ~2,000 range, patients recovering from anorexia nervosa often require substantially more. A high caloric requirement is at least somewhat intuitive during the weight restoration phase of treatment. Let’s say that during this phase, the goal is to gain two pounds per week; to gain two pounds per week, an individual would have to consume at least 1,000 calories above and beyond their usual daily requirement.
But why would over 3,000 calories a day be needed to maintain weight after weight restoration? While more research is needed to definitively answer this question, a few hypotheses offer starting points.
In order to understand these hypotheses, let’s start by thinking through what kinds of activities and physiologic processes make up total caloric expenditure (metabolism). There are three basic components of total metabolism: (1) resting metabolic rate, (2) physical activity and non-exercise activity thermogenesis, and (3) the thermic effect of food.
- Resting metabolic rate is the rate at which your body utilizes energy to function at complete rest. It fuels basic vital functions like breathing and keeping warm. A past theory to explain why those recovering from anorexia nervosa require upwards of 3,000 calories is that people with anorexia nervosa have a faster resting metabolic rate and therefore require more calories to maintain their weight. However, this hypothesis is not born out by the data. In fact, metabolic studies conducted by our group and others suggest that – similar to a starved person without anorexia nervosa – deprivation of food causes a drop in metabolic rate. This is thought to be a result of a loss of lean body mass and decreased rate of organ function which both contribute to how much energy is expended at rest.
- Physical activity and non-exercise activity thermogenesis is the energy expended for anything we do that is not resting or eating. Physical activity includes things like walking or biking, whereas non-exercise activity thermogenesis includes anything else that takes energy, like writing, typing, and even fidgeting. So, a hypothesis that may explain the higher caloric intake required for individuals following weight restoration is that those recovering from eating disorders tend to be more physically active, even unintentionally. Increased activity – even if it is something like pacing or getting up out of your chair more often – is known to be associated with increased caloric requirements for those without anorexia nervosa, so it could be that those with anorexia nervosa need those additional calories to account for the extra movement.
- The thermic effect of food is the energy needed to break down the food we eat. Ordinarily, in healthy individuals without eating disorders, the metabolic rate typically increases by about 10% after eating, which is a result of the thermic response to food. During refeeding, however, the thermic response increases to about 30%. So, as individuals are doing the hard work of eating more to recover, they may also be burning more calories breaking down that food. This exaggerated post-meal metabolic response to food may remain in effect well into the weight maintenance period.
What about estimation of calorie intake? Another hypothesis that has been proposed to explain why those recovering from anorexia nervosa tend to require more than the typical 2,000 a day, even once a healthy weight has been achieved, has to do with overestimating intake. People with a history of an eating disorder like anorexia nervosa appear to know quite a bit about the nutritional and caloric content of foods. Yet, studies have supported the hypothesis that individuals with anorexia nervosa tend to overestimate their caloric intake; repeated overestimation could lead those in recovery to be more likely to mistakenly conclude that they have met their caloric prescription. This tendency to overestimate compounded over time may be part of the reason why a higher caloric prescription is typically needed for those recovering from this eating disorder.
With these hypotheses about why people in recovery tend to require more calories to maintain their weight, we begin to have some sense of the “why.” The next question may be, “how?” Weight maintenance, especially during such uncertain times, can certainly be challenging – below you can find some additional articles that may be helpful:
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