A frustrating and often misunderstood phenomenon occurring during the nutritional rehabilitation phase of eating disorder recovery, specifically anorexia nervosa, is when patients enter a hypermetabolic state. Hypermetabolism is the significant increase in metabolic rate that develops in patients who begin eating appropriately after a prolonged period of starvation. Put simply, this means patients energy needs increase a LOT and they must significantly increase their caloric intake to reach a healthy weight. One would assume that after a long time of undernutrition, the body would ecstatically hold onto any nutrients it was given. However, research and clinical experience tell us a different story. My hope is to use this article to answer the commonly asked questions I receive as a registered dietitian about hypermtabolism during the eating disorder recovery process. But before we jump into the nitty gritty details, let’s take a moment to review the basics of metabolism.
What is Metabolism?
Metabolism is the sum total of all the chemical reactions that occur in the body for life-sustaining purposes. These chemical processes include managing hormone levels, maintaining body temperature, breathing, contracting muscles, digesting and absorbing food, eliminating waste via urine and feces, and much more. That’s right, metabolism is much more than just a vessel that makes you gain or lose weight. It takes a lot more energy to maintain life than diet culture leads you to believe, especially during the weight restoration process.
What Factors Affect Metabolism?
Contrary to popular belief, you do not have much control over the speed of your metabolism. Eating spicy foods, drinking apple cider vinegar, or closing one eye and hopping in circles while eating kale is not going to kick your metabolism into high gear. The main determining factor in your body’s basal metabolic rate is genetics, but even within families, metabolic rates can differ. Other factors influencing your metabolism include:
Muscle Mass: Muscle tissue is more metabolically active than fat tissue and therefore burns more calories at rest on a daily basis
Sex: Males typically have faster metabolisms than females
Dieting History: Signifiant dieting history negatively affects your metabolism
When most people ask me about metabolism, they are concerned about how many calories they are burning. In order to answer that, we have to look at total energy expenditure.
Total Energy Expenditure
Total energy expenditure (TEE) refers to total number of calories burned in one day when exercise is included. TEE is composed of 3 different factors:
1. Basal Metabolic Rate (BMR): 60-80%
The amount of energy needed to sustain life. This includes energy used for breathing, heart rate, cell production, and more.
2. Diet-Induced Thermogenesis: 10%
The amount of energy used for digestion, absorption, and conversion of food into energy.
3. Physical Activity Level: 15-20%
The amount of energy burned through physical activity. This number will vary depending on individual activity levels.
Effect of Food Restriction on Metabolism
One of the main reasons even the most persistent dieter will eventually regain weight is due to metabolic adaptations that occur as a result of food restriction and attempts to lose weight. Metabolic adaptation refers to the slowing of the metabolism in response to large amounts of weight loss, resulting in fewer calories being needed to maintain normal weight. This occurs because your body’s physiology wants to protect you from starvation-induced malnutrition. From an evolutionary standpoint, this is genius. Your body is able to recognize that inadequate food is coming in over an extended period of time and fine tune its metabolic efficiency to expend less energy, thus keeping you alive longer. Once food intake is returned to normal, metabolic rate increases. Unfortunately, our modern-day “thin is better” culture doesn’t appreciate this.
For an individual with long-standing anorexia, the effect of malnutrition on their metabolism is a bit different. Their metabolism returns back up to normal, but it doesn’t stop there. For many of them, they experience a long bout of increased energy expenditure via hypermetabolism.
What is Hypermetabolism?
The knowledge of a slowing metabolism with food restriction and weight loss leads to an increased fear of eating for my patients. Many of them believe they have “broken” and they are shocked to hear of the high energy requirements needed during recovery. Although I jokingly tell them that would make my job much easier as their dietitian, weight gain during recovery from anorexia is much more difficult than they imagine. In response to increasing food intake during the early stages of recovery, the body becomes hypermetabolic, resulting in a faster than usual metabolism and increase in nutrient needs. While the exact reason for this is unknown, it occurs almost universally in patients restoring their weight.
This phenomenon is responsible for the all too often “You want me to eat how much!?” conversation in my office. Patients and their loved ones are often shocked when I have to increase meal plans multiple times to produce even the slightest bit of weight gain. Parents will tell me “But, they have never eaten that much food in their life! Not even while playing competitive sports.” I think I speak for most dietitians when I say, I don’t make the rules, I just make the meal plans. This is one major reason it is vital to seek professional help.
Meal Plan for Hypermetabolism
It’s widely agreed upon that the initial primary goal in treatment for anorexia nervosa has to be full weight restoration. This is a critical step in reestablishing physical, mental, and emotional well-being. Unfortunately, this is often one of the most difficult steps for my patients. They are being asked to face their biggest fear 6 times per day every single day. For reference, eating disorder treatment often involves the consumption of 3 meals and 3 snacks per day.
Not only are they faced with the fear of eating, they are forced to deal with the physical repercussions of increasing food intake after a long period of starvation. As mentioned earlier, they become metabolically inefficient and require a significantly larger number of calories than usual just to maintain their weight.
For an adult woman recovering from anorexia who is hypermetabolic, this means consuming 2-5x the amount of calories compared to a healthy adult woman. This is when I often get asked, “How do I need this much food if 3,500 kcal equal 1 pound?” It’s true that a lot of science books reference the 3,500 kcal rule when it comes to gaining 1 pound, but it’s just not that simple. Research shows that a patient who is hypermetabolic may require up to 5,000 – 10,000 excess kcal to gain 1kg, which equals 2.2 lbs. If there is one thing as an eating disorder dietitian I know for sure, it is that there is no normal when it comes to meal plans and everyone’s required energy intake is extremely individualized.
It’s important to note that even on relatively high meal plans, weight loss in the first couple weeks of treatment often occurs as a result of the increased metabolic rate. This can be confusing and frustrating for patients and their families, but is a normal part of the refeeding process.
What Causes Hypermetabolism?
While the exact reason why someone may experience hypermetabolism is unclear, research suggests that patients experience an increased thermic effect of food, meaning that energy is converted into heat rather than being used to build new tissue. This is often experienced as night sweats when patients wake up with soaked sheets. Recent studies show that individuals with anorexia become hyperthermic (elevated body temperature) at night, which is normally when body temperature decreases. Some believe this may be due to changes in hormones.
How Long Does Hypermetabolism Last?
Although it is different for everyone, research shows a patient can be hyper metabolic anywhere from 3-6 months after full weight restoration with some articles stating it can last up to 1 year.
Remember...
Recovery is possible, but it takes time and it’s never a straight and narrow path. Your body and mind need time to heal and consistency, rather than perfection, is most important. Expecting results after just a couple weeks or months is unrealistic if you or a loved one has been struggling for awhile. The body is smarter than we think and knows how to heal when you give it the nutrients and self-care it asks for. As a reminder, it is vitally important to reach out to your medical doctor and registered dietitian if you believe you or someone you love is recovering from an eating disorder.
As always, contact me with any questions you may have and click below to read more of the Nutrition Musings blog.
Kelly Melanson, Registered Dietitian
