Most people with bulimia nervosa do not lose weight. Despite the binge-purge cycle being driven by a desire to control weight, the majority of people with bulimia maintain a weight in the normal BMI range, and many eventually gain weight over time. The reasons come down to basic biology: purging is far less effective at eliminating calories than most people assume, and the cycle itself triggers metabolic and hormonal changes that work against weight loss.
Why Purging Doesn’t Remove Most Calories
The body begins absorbing calories almost immediately after food enters the stomach. A study published in the American Journal of Psychiatry measured exactly how many calories people with bulimia retained after vomiting and found something striking: regardless of binge size, the body kept roughly the same amount. Participants who ate smaller binges averaging about 1,550 calories retained around 1,128 calories after vomiting. Those who ate larger binges averaging 3,530 calories still retained about 1,209 calories. In other words, vomiting removed some of the excess from a large binge but left behind more than a thousand calories every time.
This creates a ceiling effect. The body absorbs a baseline amount of calories no matter what, so larger binges don’t mean proportionally more is purged. Someone who binges and purges multiple times a day can easily retain several thousand calories, which is more than enough to prevent weight loss and often enough to cause gradual gain.
Laxatives and Other Methods Are Even Less Effective
Laxatives work on the lower end of the digestive tract, well after the small intestine has already absorbed nearly all the calories and nutrients from food. The weight that drops after laxative use is almost entirely water. It returns as soon as the body rehydrates, which it will do quickly because chronic laxative use triggers fluid retention. The same is true for diuretics. Neither method meaningfully reduces calorie absorption.
What Happens to Weight Over Time
Research tracking people with bulimia over several years reveals a consistent pattern: weight tends to increase, not decrease. Many people with bulimia were once at a higher weight before the disorder began. Studies of outpatients found they had lost an average of about 9.6 kilograms (roughly 21 pounds) from their highest previous weight, while residential patients showed an average loss of about 12 kilograms (26 pounds). But this weight suppression doesn’t last.
A five-year longitudinal study found that participants’ weights increased over the study period, and those who had lost the most weight before the study gained it back the fastest. Researchers describe this as a “biobehavioral bind”: suppressing weight through binge-purge cycles may temporarily reduce feelings of being overweight, but it fuels more binge eating and purging, which eventually leads to weight regain. That renewed weight gain triggers more intense dieting, which drives more bingeing, creating a self-reinforcing cycle.
How Bulimia Changes Your Metabolism
Chronic binge-purge cycles alter the body’s resting energy expenditure, which is the number of calories you burn just by existing. There is evidence that people with bulimia have a reduced resting metabolic rate. When someone loses weight through any means, the body responds by becoming more energy-efficient, burning fewer calories at rest and adjusting hunger hormones to promote weight regain. This process, sometimes called adaptive thermogenesis, is especially pronounced in bulimia because the cycles of restriction and bingeing send chaotic signals to the body’s metabolic systems.
Hormones involved in hunger and fullness also become disrupted. The binge-purge cycle reduces the release of gut hormones that normally signal fullness after eating, which makes it harder to feel satisfied by normal portions. Meanwhile, insulin responses become altered in ways that increase nausea and the urge to vomit after eating, reinforcing the purging behavior. Over time, these hormonal shifts make both normal eating and weight stability harder to maintain.
Why People With Bulimia Can Look Heavier
Bulimia can actually change facial appearance in ways that make someone look like they’ve gained weight, even when their body weight hasn’t changed much. Repeated vomiting stimulates the parotid glands (the large salivary glands near the jaw) through constant contact with stomach acid and enzymes. Over months and years, these glands enlarge, sometimes significantly. This creates visible swelling along the jawline and cheeks that gives the face a rounder, puffier appearance. In severe cases, the swelling is dramatic enough that surgical removal of the glands is the only effective treatment.
Fluid retention adds to this effect. Purging causes the body to lose water and electrolytes, and in response, the kidneys compensate by holding onto more fluid. This leads to bloating and puffiness that can register on the scale and in the mirror, particularly in the hands, feet, and face.
What Happens to Weight During Recovery
One of the most challenging aspects of recovery is that stopping purging often leads to temporary weight gain before the body recalibrates. When someone stops vomiting or using laxatives but binge eating persists for a period, more calories are retained. The body’s metabolism, which has been suppressed, takes time to normalize. Fluid that was chronically depleted gets restored, adding water weight.
This initial weight fluctuation is one of the most common reasons people relapse. Clinicians working with bulimia patients note the importance of understanding that metabolism takes time to stabilize after the cessation of binge-purge cycles, and that small weight fluctuations during this period do not represent permanent changes. For most people, weight stabilizes within several months as eating patterns normalize and the body’s metabolic and hormonal systems recalibrate.