THE METABOLISM, HYPERMETABLOLISM AND IMPLICATIONS FOR RECOVERY FROM A RESTRICTIVE EATING DISORDER
A question that arises regularly from people in recovery from an eating disorder (ED) is in respect to issues around the body metabolism – what it is; what hypermetabolism is; whether they have ‘broken’ their metabolism and what it means for their recovery.
I hope to address a lot of the common concerns people experience around this topic in this post.
If you have had or have disordered eating then it is likely that your body metabolism has been affected at various points as a result, impacting on the body’s ability at those times to lose or gain weight and to function at an optimal level.
What Is The Body Metabolism?
Metabolism describes all the chemical processes that go on continuously inside the body to keep you alive and well; the organs functioning normally so that the heart beats and lungs work to breathe, cells repair, the gut digests food and the brain can think.
Even when completely resting therefore the body is using up calories to maintain basic function.
The minimum amount of energy required to carry out these resting chemical processes is called the basal metabolic rate (BMR) which accounts for anything between 40% and 70% of your body’s daily energy requirements depending on other factors such as age, lifestyle, the body make up and your environment.
When the body is starved, its tissue, including muscle and fat, is lost from the body and this lowers the metabolic rate.
If the body does not have sufficient energy intake (food) it will try to preserve the energy it does get and does so in several ways (often referred to as the body going into ‘starvation mode’).
These include providing less nutrients to hair, skin and nails (so they become dry and brittle); the heart rate slows down, gut motility slows and body temperature drops (often leaving the person feeling cold most of the time).
This ultimate drop in the BMR means that the body needs less calories to function but at a very basic level, ultimately just staying alive.
This same drop in BMR will happen in the body when intake is dropped for any reason – so in eating disorders this will occur when the person is not eating sufficiently or is compensating for what they are eating (e.g. via exercise).
However, the same response occurs when people drop their intake for other reasons, including people who diet and it explains why those who diet may initially lose weight rapidly but after a couple of weeks of dieting will find it much harder to sustain weight loss as their BMR has fallen and they are using less baseline energy.
Once a person who has had a low BMR starts to eat more again and provide the body with the energy it requires, the opposite is true and the metabolism will start to rise again, meaning that the body requires more energy (food) in the future just to maintain basic function.
The Metabolism In Eating Disorder Recovery
In ED recovery weight restoration and nutrition are key components to treatment, restoring the body to its natural set point weight.
This weight gain results in ultimate improvements in the physiological and psychological complications of semi starvation.
In order to achieve weight gain patients with AN ultimately need to increase their dietary intake to a level that is above that required for BMR AND daily activities AND then enough to restore weight in terms of tissue re-development and internal repairs.
To achieve regular weight gain people with AN generally need an escalating calorie intake.
Research has found that women with AN tend not to gain weight if fed the energy requirements of healthy adult women who have never had an ED. Instead people with AN in recovery generally have much larger energy requirements and need to increase their intake more and more for sustained weight gain.
The reason for this can be explained since people with AN are often found to become hypermetabolic once they increase their dietary intake sufficiently – so their metabolic rate is higher than the average rate expected in a healthy adult woman.
Hypermetabolism in people with AN means that they will generally lose weight easily and need a larger amount of food than most to gain weight.
People with AN also convert more of their energy intake to heat than healthy women, rather than use the excess intake to build tissues. As a result, during refeeding people with AN often become hot and sweaty. Commonly this can be worse at night with it not being uncommon for people in AN recovery to wake in the night sweating & with soaking sheets.
This is referred to as becoming hyperthermic.
Conversely, healthy individuals who have never had an ED will generally drop their body temperature at night and so preserve energy at this time.
It is thought that the hyperthermic effect in AN refeeding results in up to 30% of energy input being lost (in healthy controls the rate is generally around 14%).
To fully weight restore the body needs to restore fat mass as well as fat free mass.
To gain fat mass the energy requirement is generally 6 times greater than fat free mass, making this vital latter stage of weight restoration even harder to achieve and needing even more food (energy) to achieve the same rate of gain.
Once weight restored after AN it has also been found that energy requirements remain elevated – those with AN in recovery are found to still be very energy inefficient and need greater calorie intake than healthy controls just to maintain their restored weight.
It is not uncommon that weight restored AN patients need up to twice the daily calorie intake to healthy adults just to maintain weight due to continued hypermetabolism.
This hypermetabolism can settle down in 6 months of weight restoration but it is widely recommended that the best chance of long term weight maintenance in recovery is to persist with high calorie intake long term.
So what does all this mean if you are in recovery from AN?
For any patient in recovery from AN it is likely that once you are providing your body with sufficient energy on a daily basis your body metabolism will speed up to a greater rate than in healthy individuals.
Therefore, you will likely find that your energy requirements to keep gaining weight will keep rising and as you start to fully restore fat mass towards the the end of weight restoration, your energy needs are likely to be extremely high.
In weight restoration you might find that you are warm or hot a lot of the time and experience night sweats or clamminess.
You will possibly notice a rise in your heart rate.
You should also start to notice better nails, hair and skin.
Once you have fully weight restored the level of intake (food) you need every day to maintain this healthy weight is likely to be significantly higher than healthy adults of your age and build and this higher energy need could continue for a significant amount of time.
In conclusion – the amount of food needed now to restore weight and once weight restored is likely to be much more than you think and the body will respond to the energy levels it is given.
Therefore -eat large amounts to weight restore and keep eating large amounts well into recovery!
And Finally, But.. Is My Metabolism Broken??
One question that is often posed from people in recovery from restrictive eating disorders who have been weight restoring while still actively restricting or actively exercising is –
…‘but what will happen now if I do stop restricting or stop exercising?
I am already back at a ‘healthy weight’ – won’t I just then become massively overweight? Have I broken my metabolism forever??’.
If this describes your situation or your fears then please don’t despair!!
You are not broken!
It is very likely that as you have still been restricting your intake and exercising then your body metabolism has remained in ‘starvation mode’ (very low) to preserve what it is being given. Your body used the small amount of surplus energy you did provide it with to restore your weight and try to repair tissues causing some weight gain but the body recognised that there was still insufficient energy supply to allow it to speed up the base metabolism and function at its optimum.
This can still be changed.
If you start to eat more now – stop restricting your dietary intake and give your body the amount of fuel it desperately still needs and if you stop compensating for what you are eating if you are still exercising then the body will respond.
The body will learn to trust that fuel is in sufficient supply so it can ‘afford’ to work at a more optimal level and your metabolism will, as discussed earlier in this article, respond and speed up. It is never too late for this to occur.
In the initial stages of the process you might gain a little more weight but if you eat unrestrictedly, without compensating, then the metabolism and the body weight will naturally settle back at your genetic set point and your body will fight to keep your weight level there.
Marzola et al. Nutritional Rehabilitation in Anorexia Nervosa: review of the literature and implications for treatment. BMC Psychiatry (2013) 13:290