Sister Lies About Having Her Autoimmune Disease To Excuse Weight Gain, She Finally Snaps

Being honest about illness is hard enough without someone else claiming it for their own benefit. When health conditions become tools for sympathy, the line between insecurity and deception can blur in deeply uncomfortable ways.

One woman found herself confronting that reality after realizing her sister had been passing off her diagnosis as her own. The discovery forced a long history of favoritism, denial, and misplaced expectations into the open.

What followed was not a simple conversation but a cascade of tears, defensiveness, and parental pressure to once again take the higher road.

As tensions rise, she is now questioning whether her reaction was too harsh, or whether this was a moment that demanded honesty, no matter how uncomfortable it made everyone else feel.

A woman confronts her sister for claiming her medical condition to excuse weight gain

Medical conditions and body weight are often misunderstood, and misinformation can spread easily when people assume symptoms without factual grounding.

In this story, the OP’s sister has repeatedly claimed a medical diagnosis that belongs to someone else, not to explain her own weight, but to gain sympathy from others. That behaviour goes beyond mere misunderstanding and reflects a pattern best described as sympathy-seeking through misrepresentation.

First, it’s important to understand what Hashimoto’s thyroiditis is and isn’t. Hashimoto’s is a chronic autoimmune condition in which the body’s immune system attacks the thyroid gland.

Over time, this can lead to low thyroid hormone levels (hypothyroidism), which can affect metabolism and lead to symptoms such as fatigue, mild weight gain, cold intolerance, and other systemic effects.

This condition is diagnosed through specific blood tests and ongoing evaluation by a healthcare provider. It cannot be self-diagnosed or assumed based on body size alone.

Hashimoto’s is most commonly diagnosed through laboratory tests for thyroid-stimulating hormone (TSH), T4 hormone levels, and antithyroid antibodies, and many people with the condition require lifelong medication like levothyroxine to manage hormone levels. Symptoms vary widely and often develop gradually over years.

It’s also worth noting that while hypothyroidism can contribute to weight gain, it is not usually the primary driver of significant changes in body weight for most people. The relationship between thyroid function and obesity is complex and influenced by many factors, including genetics, metabolism, diet, and physical activity.

Some studies show a higher frequency of overweight or obesity in people with autoimmune thyroiditis, but the overall connection does not establish that thyroid disease is the main cause of weight issues for everyone who is overweight.

From a behavioural perspective, repeatedly claiming someone else’s medical diagnosis to explain one’s own circumstances can be framed in psychological literature as sympathy-seeking behaviour.

A modern term for one form of this is “sadfishing,” which refers to sharing or exaggerating emotional or personal problems in order to attract sympathy and attention from others. This can happen online or in real-life interactions.

Sadfishing doesn’t necessarily indicate a diagnosable disorder, but research and commentary in psychology highlight that such patterns are often tied to a desire for validation, social support, or emotional attention, even when the reported problem is inaccurate or exaggerated.

In this context, the OP’s frustration with their sister’s repeated misrepresentation, claiming the OP’s medical condition as her own to justify weight issues, is understandable.

It not only distorts a real medical diagnosis, it also undermines genuine understanding of thyroid disorders and contributes to stigma and misinformation around both illness and weight.

Effective support and empathy for someone struggling with body image should come from honest understanding of their experiences, not inaccurate medical narratives.

Here’s what people had to say to OP:

These commenters called the sister jealous, narcissistic, and in need of therapy

This group was outraged she tried to steal meds and fake a serious illness

These Redditors blamed the parents for enabling lies and avoiding accountability

This group questioned family dynamics and said multiple members need therapy

These commenters discussed body dysmorphia, fatphobia, and misplaced blame

Many readers sided with the woman who refused to let her illness be repurposed as a shield, while others saw years of untreated insecurity finally boiling over.

Do you think calling out the lie was necessary, even if it hurt? Or should compassion have come first, regardless of the facts? Where would you draw the line when your own health becomes someone else’s excuse? Share your thoughts below.