Marina, 41 years old, lost 18 kg in eight months using tirzepatide to treat obesity. Her lab work improved, clothes in her closet no longer fit, and yet every time she passes through a doorway, she still shrinks back a little, afraid she won't fit. When she looks 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 fictitious and are merely illustrative, serving to facilitate understanding of the topic addressed."

This mismatch has a name, 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 media, 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 described in bariatric surgery patients; studies show that many of them maintain an identity of "obese person" even 18 to 30 months after surgery. With weight-loss pens, the phenomenon has returned to discussion because weight loss tends to be faster than with traditional diets, which seems 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 one occupies space, and even self-protective behaviors (such as choosing the "right" chair or avoiding tight spaces). When the body changes too quickly, this mental construction simply doesn't have time to keep up.

It's 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 over time as the new body reality 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 vigilance 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 behavioral experimentation, exposing oneself repeatedly and concretely to situations that the "old body" avoided, helps update this mental image more quickly. Sitting without checking first if you fit, crossing a narrow gap without shrinking back, allowing yourself to accept invitations that would have been refused before: each repetition functions as new data for the brain to process.

When to seek help

Feeling this mismatch in a temporary way is common and, in most cases, does not indicate a problem. But if the discomfort with one's own image is persistent, interferes with mood, relationships or routine, or comes accompanied by restrictive eating behaviors, it's worth talking to the doctor responsible for the treatment or seeking specialized psychological support. Recent international guidelines already recommend that GLP-1 treatment be accompanied by behavioral support, precisely to address 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 by a qualified healthcare professional. Always seek individualized medical guidance.

Dr. Rebeca Soares Andrade CRM - GO 39335