Bulimia: What Purging Actually Does to the Body

Bulimia is usually described in terms of behaviour — eating and then compensating. That description is accurate and almost useless, because it explains nothing about why the illness is dangerous, why it is so hard to stop, and why the person doing it is frequently the last to understand what is happening to their body.

This article is about the physical side. Not because the psychological side matters less, but because the physical facts are the ones people are most often wrong about, and being wrong about them keeps the cycle running.

🔄 The loop, and why it tightens

The cycle has a shape that repeats regardless of who is in it, and each stage feeds the next in a way that is close to mechanical.

The important part is the third stage. Compensation is enormously reinforcing, not because it does what the person thinks it does, but because it reliably removes an unbearable feeling within a short time. That is exactly the learning pattern that makes a behaviour hard to give up, and it is why willpower is such a poor tool against it.

The second important part is that restriction is the engine, not the binge. Treatment that focuses on stopping the binges without addressing the restriction almost always fails, because the restriction is what generates the next binge.

🫀 The complication that kills people

Most people with bulimia are worried about their weight. Almost nobody is worried about their potassium, and potassium is the thing that ends lives.

Vomiting, laxatives and diuretics all remove potassium from the body. Potassium is what allows heart muscle to reset electrically between beats. When it falls far enough, the heart becomes prone to abnormal rhythms, and some of those rhythms are fatal within minutes.

Vomiting also strips the body of acid, which pushes the blood chemistry in an alkaline direction and makes the kidneys hold onto acid while dumping more potassium. The result is that the two problems reinforce each other. Laxatives and diuretics produce a related but different disturbance, and diuretics also lower sodium, which at low enough levels causes confusion and seizures.

None of this requires years of illness. It can develop during a single intensive period.

🦷 The damage that does not reverse

Stomach acid dissolves tooth enamel, and enamel does not grow back. This is the one permanent consequence of bulimia in someone who otherwise recovers fully, and it is often the reason the illness is discovered.

The pattern is distinctive enough that dentists recognise it immediately: erosion on the inner surfaces of the upper front teeth, where acid pools, while the outer surfaces look normal. Fillings begin to stand proud of the tooth surface around them, because the filling material does not dissolve and the tooth around it does. Sensitivity to cold and sweetness arrives early. Teeth become shorter, translucent at the edges, and yellower as the darker layer beneath shows through.

Two practical points are worth more than any amount of general advice here.

Alongside the teeth, the salivary glands in front of the ears frequently swell, giving the face a rounded appearance. This is a benign response to repeated vomiting and it settles after purging stops, though it can take weeks and it often becomes temporarily more noticeable at first — a detail worth knowing, because it is deeply demoralising to someone who has just stopped.

💧 What each method actually achieves

This section exists because the beliefs behind these behaviours are factually wrong, and correcting them is one of the few pieces of information that changes what people do.

The laxative row deserves emphasis because the misunderstanding is so complete. Digestion and calorie absorption finish in the small intestine. Laxatives work on the colon, which is downstream of all of it, and whose main job is reclaiming water. So the only thing a laxative removes is water. The number on the scale falls, which appears to confirm the theory, and it returns the following day, which is taken as evidence that a larger dose is needed.

Prolonged use makes the bowel dependent, so that normal function does not resume without them. Stopping then produces days of constipation and bloating, which feels like proof that they were necessary. They were not. That phase passes, and it passes faster with fluid, fibre and time than with another dose.

📈 The trap in the first weeks of stopping

This is the least known and most destructive thing in the whole subject, and it is the reason a great many attempts to stop fail in the first fortnight.

When the body has been losing fluid repeatedly through purging, laxatives or diuretics, it responds by producing hormones that make it hold onto salt and water. Those hormones stay elevated for a while after the losses stop. So when someone stops purging, the retention system is still running at full strength with nothing to counteract it, and the body holds water.

The result is swelling of the hands, feet, ankles and face, and a rapid rise on the scale — sometimes several kilograms within days. To someone who has just made an enormous effort to stop, this looks exactly like the catastrophe they were purging to prevent.

🩸 Insulin omission

Among people with type 1 diabetes there is a form of compensation that has no equivalent in anyone else: deliberately reducing or skipping insulin so that glucose is lost in the urine rather than stored.

It is effective at causing weight loss, which is why it happens, and it is among the most dangerous behaviours in this entire field. It drives blood sugar high, causes severe dehydration, and can produce a life-threatening metabolic emergency. Repeated over time it accelerates damage to eyes, kidneys and nerves by many years, and it substantially shortens life expectancy.

It is under-recognised because the signs — unexplained high readings, repeated ketoacidosis, weight loss, missed appointments — are usually read as poor self-management rather than as an eating disorder. Anyone with type 1 diabetes whose control has become erratic alongside weight concerns needs assessment for this specifically, and needs care from a team that handles both problems together rather than each separately.

🔍 Why it goes unnoticed for years

The single most persistent myth about bulimia is that a person with an eating disorder is visibly underweight. In bulimia that is usually not the case. Most people with bulimia are within a normal weight range, and some are above it. Nothing about their appearance suggests illness.

The behaviour is also concealed with considerable skill, and the shame surrounding it makes disclosure exceptionally difficult — more so than with restriction, which is sometimes admired before it is recognised as a problem. Bulimia is rarely admired by anybody, including the person doing it.

What is actually visible, if anyone knows to look, is a set of physical signs rather than a body shape.

None of these is proof on its own. Several together, in someone preoccupied with weight, is a reason to ask directly and kindly.

🧠 What treatment actually consists of

Bulimia has better outcomes than most people expect, and the evidence for what works is unusually clear.

Psychological therapy is the primary treatment — specifically the forms designed for eating disorders, which work on the restriction that drives the binges rather than on the binges themselves. Guided self-help programmes based on the same principles are effective for a substantial number of people and are far more accessible than specialist therapy in most places, which matters when waiting lists are long.

The core of it is establishing regular eating: consistent meals across the day, without gaps long enough to generate a binge, and without compensating afterwards. This is enormously difficult and it is also the single most effective intervention. Most of the improvement in binge frequency follows from it.

Medication is an adjunct rather than a treatment on its own. It reduces binge and purge frequency, and it works best combined with therapy rather than instead of it.

Alongside therapy and medication, the physical side needs monitoring in its own right: potassium and other electrolytes checked where purging is frequent, dental review, and specific attention to bone health where periods have stopped for any length of time. The overview of eating disorders covers how the different conditions in this family relate to one another and how they move between each other over time.

📆 What recovery looks like from inside

The honest version is more useful than the encouraging one, because people who expect a straight line give up when they do not get it.

The first weeks are physically uncomfortable. Fluid retention and swelling, bloating, constipation if laxatives were being used, and a stomach that empties slowly and makes normal meals feel enormous. All of this is temporary and all of it feels like evidence that stopping was a mistake.

Anxiety rises before it falls. Compensation was doing a job — relieving fear — and removing it leaves the fear with nowhere to go. That period is what therapy exists to get someone through, and it does pass.

Lapses are part of the pattern, not the end of it. The difference between a lapse and a relapse is almost entirely what happens next: whether the person returns to regular eating the same day, or responds with restriction, which restarts everything.

The physical repair is mostly complete. Electrolytes normalise, the salivary glands settle, the gut recovers, periods return, and the swelling resolves. The enamel does not, which is the one argument for acting sooner rather than later that has nothing to do with how bad things feel today.

🤝 Saying something to someone else

Two things reliably fail. Commenting on appearance or weight, in any direction, because it confirms that bodies are what is being watched and judged. And policing food or bathroom visits, which turns the illness into a contest and drives it further out of sight.

What works better is unremarkable: naming what has been noticed without accusation, saying it privately and once rather than repeatedly, making clear that the offer of help stands whether or not it is taken today, and being willing to sit through the denial that usually comes first. Denial at the first attempt is close to universal and it is not a refusal — it is frequently the moment someone realises they have been seen, which is what eventually makes asking for help possible.

🩺 When to seek help

• Chest pain, palpitations, an irregular heartbeat or fainting in anyone purging — emergency
• Severe muscle weakness, or weakness in the legs — urgent, and a potassium level is needed
• Confusion or a seizure, particularly where diuretics have been used — emergency
• Vomiting blood, or severe chest or abdominal pain after vomiting — emergency
• Difficulty swallowing, or persistent hoarseness — needs assessment
• Erratic blood sugars in type 1 diabetes alongside weight concerns — assessment for insulin omission
• Any purging happening more than occasionally — specialist referral, not watchful waiting
• Before stopping, where purging has been frequent or laxative use heavy — medical supervision through the first weeks
• Tooth sensitivity or visible wear — dental review, with the cause stated

Treatment support is available in the antidepressants category, including Sertafine (sertraline), and Topamax (topiramate), which is sometimes used to reduce binge frequency under specialist supervision. Medication in bulimia works alongside psychological treatment rather than in place of it, and prescribing decisions here depend on information the prescriber can only have if it is given to them.

❓ Frequently asked questions

📑 Sources and editorial

• Diagnostic criteria for bulimia nervosa and the 2013 removal of purging and non-purging subtypes
• Clinical literature on hypokalaemia, metabolic alkalosis and cardiac arrhythmia in purging behaviour
• Dental literature on perimylolysis and enamel erosion patterns in self-induced vomiting
• Evidence on the site of calorie absorption and the absence of any effect of stimulant laxatives on it
• Literature on pseudo-Bartter syndrome and rebound oedema following cessation of purging
• Guidance on insulin omission in type 1 diabetes with disordered eating
• Trial evidence for fluoxetine in bulimia nervosa and its licensed indication
• Contraindication of bupropion in current or prior eating disorders on seizure-risk grounds
• Guideline recommendations for eating-disorder-focused psychological therapy and guided self-help
• Related reading: understanding eating disorders, how body fat actually works, psychiatric drug classes
• Related products: antidepressants category
• RXshop Editorial Team — reviewed by Emily Chen, MD, Internal Medicine