Marina, 41 years old, lost 18 kg in eight months using tirzepatide to treat obesity. Her test results improved, clothes from her wardrobe no longer fit and yet, every time she passes through a doorway, she still shrinks a little, afraid she won't fit. When she looks at herself in the mirror, the body she sees is not quite the body that is there.
"The data and clinical case cited in this article are fictional and are merely illustrative, serving to facilitate understanding of the subject matter addressed."
This mismatch has a name, and it is being increasingly reported by those who use these medications and has an explanation in the way the brain constructs our body image.
What is "phantom fat"
The phenomenon is called, in the literature and on social networks, phantom fat or ghost fat — "phantom fat". It describes people who have lost a significant amount of weight but continue to perceive themselves as if they were in a larger body. The comparison most commonly used by researchers themselves is with phantom limb: just as the brain can continue to "feel" an arm or leg that no longer exists after an amputation, it can also take time to update the mental map of its own body after a rapid physical change.
This type of mismatch between body and mind was already being described in bariatric surgery patients; studies show that a large proportion of them maintain an identity of "obese person" even 18 to 30 months after surgery. With weight-loss pens, the phenomenon returned to discussion because weight loss tends to be faster than with traditional diets, which appears to intensify the mismatch.
Why this happens
Body image is not a passive mirror of physical reality, it is a construction that the brain assembles over years, based on habits, posture, the way of occupying space and even self-protective behaviours (such as choosing the "right" chair or avoiding tight spaces). When the body changes too quickly, this mental construction simply does not have time to keep up.
It is worth highlighting an important distinction: phantom fat is not a clinical diagnosis. It differs from body dysmorphic disorder, which involves distorted and persistent beliefs about one's own appearance. Phantom fat tends to be more of an update delay, the brain "holding onto" an old image out of habit and, for most people, tends to resolve itself over time, as the new reality of the body is repeatedly confirmed.
Research also points out that people with greater interest in GLP-1 medications already arrive at treatment with more shame about their own body, more surveillance regarding appearance and lower body appreciation — which suggests that those who already had a more difficult relationship with their own image may be more vulnerable to this type of mismatch during weight loss.
What helps the brain "catch up" to the new body
Experts point out that behavioural experimentation, exposing oneself, in a repeated and concrete manner, to situations that the "old body" avoided helps to update this mental image more quickly. Sitting without first checking if you fit, crossing a gap without shrinking, allowing yourself to accept invitations that would previously have been refused: each repetition works as new data for the brain to process.
When to seek help
Experiencing this mismatch in a temporary way is common and, in most cases, does not indicate a problem. But if the discomfort with your own image is persistent, interferes with mood, relationships or routine, or is accompanied by restrictive eating behaviours, it is worth talking to the doctor responsible for your treatment or seeking specialised psychological support. Recent international guidelines now recommend that treatment with GLP-1 be accompanied by behavioural support, precisely to deal with these changes in identity and body image that accompany weight loss.
This content is informational in nature and does not replace consultation, diagnosis or treatment with a qualified healthcare professional. Always seek individualised medical guidance.
Dr Rebeca Soares Andrade CRM - GO 39335