Why Do Weight Changes Happen in Ankylosing Spondylitis?

The pain may make it feel impossible to achieve a healthy weight

Ankylosing spondylitis (AS) can affect your weight. It can either cause a loss of appetite, leading to unintended weight loss, or the pain and discomfort associated with AS can limit physical activity, resulting in weight gain.

This article discusses these connections and what you can do to maintain a healthy weight if you live with this disease.   

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What Makes AS Worse, Losing or Gaining Weight?

The severity and symptoms of AS can vary from person to person. The relationship between AS and weight further complicates matters.

Research has found that neither being overweight or obese nor being underweight is good if you have AS. Both body types lead to increased disease activity, making symptoms more severe and responses to treatment less successful.

Unintended Weight Loss From Inflammation

Inflammation is the body's immune response to cell damage or infection. Ankylosing spondylitis is a chronic inflammatory condition that directly affects the spine's joints. In severe cases, broader effects include:

  • Fatigue and lack of energy
  • Fever
  • Inflammation in the digestive system, such as Crohn's disease and ulcerative colitis
  • Loss of appetite

As a result of these symptoms, eating healthy becomes difficult. Dietary changes may lead to unintended drops in weight and can cause malnutrition, a condition in which the body doesn't get the nutrients it needs. These are common complications of AS, and complications are more pronounced in people the longer they live with the condition.

Studies have linked these symptoms to increases in specific inflammatory biomarkers, which offer clues to identifying any underlying disease. Proteins, known as cytokines, are biomarkers that may directly affect appetite centers in the brain. One study found that about 23.8% of AS patients experience malnutrition.

Ankylosing Spondylitis and Eating Disorders

Ankylosing spondylitis is associated with eating disorders. Researchers found that chronic autoinflammatory conditions like AS significantly raise the risk of developing anorexia nervosa and bulimia.

Increased Joint Pain From Being Overweight

The stiffness, pain, and intense fatigue associated with AS can cause people to avoid physical activity and gain weight. Medications prescribed for the condition, tumor necrosis factor (TNF) blockers, can also cause weight gain as a side effect.

The added weight from being overweight or having obesity puts excess strain on the joints. People with AS experience more pressure on the vertebrae (the bones in the spine), which increases pain. This increased strain contributes to advanced disease progression and damage to affected areas.  

Hormonal Fluctuations, AS, and Weight

C-reactive protein is a biomarker for bodily inflammation. Rises in estrogen (a hormone associated with female sex characteristics but also present in men) lower the body's C-reactive protein concentration, causing an anti-inflammatory effect. Decreases in estrogen levels due to aging or as the result of the menstrual cycle can lead to weight gain.  

How to Reach a Healthy Weight With AS

Weight changes with AS can impact the progression of this disease. Maintaining a healthy weight is recommended to manage this condition.

If you aim to gain weight, here’s what you can try:

  • Boosting your physical activity to stimulate your appetite
  • Eating small meals throughout the day, especially if you get full quickly
  • Eating nutrient-rich snacks throughout the day, such as nuts or dried fruit
  • Incorporating healthy, unsaturated fats into your diet
  • Making eating a social event and dining with others

If you aim to manage AS and lose weight, try the following:

Obesity as a Risk Factor for AS

Research has found that the biomarkers associated with inflammation due to AS are also associated with obesity. This connection indicates that clinical obesity may be a risk factor for AS.

While the exact relationship is still being researched, there’s considerable overlap between clinical obesity and AS. A cross-sectional analysis of weight status in people with axial spondyloarthritis (AS is a severe form of spondyloarthritis) found that 22% of the subjects experienced obesity, compared to 15% of the general population participating in the study.


Ankylosing spondylitis (AS) has a complex relationship with body weight. In some, it causes unintended weight loss and malnutrition. Others with AS may gain weight due to inactivity from the condition. Being diagnosed with clinical obesity or overweight can make AS worse. Maintaining a healthy body weight by practicing moderate exercise, good sleep habits, and adhering to a well-balanced diet is vital in managing this disease.    

A Word From Verywell

It’s challenging to live with a chronic inflammatory condition like AS. Without a cure, there is always the risk of flare-ups and periods of pain and discomfort. However, with medical help and lifestyle changes, you can effectively manage this condition. The key is to be proactive; if you’ve been diagnosed with AS, talk to your healthcare provider and learn ways to manage your condition.

Frequently Asked Questions

  • What foods should you avoid with ankylosing spondylitis?

    Though more work is needed, researchers have found that certain foods can impact inflammation in the body, which may worsen AS cases. Your healthcare provider may advise an anti-inflammatory diet to help with symptoms. This means avoiding gluten (a protein found in wheat, rye, and barley), processed foods, fried foods, artificial flavorings, and an excess of red meat, sugars, and salts.

  • What can you do to lose weight during an ankylosing spondylitis flare?

    Low-impact activities, such as walking, cycling, and swimming, are good exercise options during an AS flare. Be mindful of how you feel, and don’t push yourself if you are in pain. Incorporate fresh fruits, vegetables, multigrain bread, and healthy fats into your diet. Limit added sugars, salts, processed foods, and saturated and trans fats. 

  • Is it safe to fast with ankylosing spondylitis?

    Some research has connected intermittent fasting and improvements in inflammatory conditions like AS. Ensure you are following the right plan and talk to your healthcare provider to learn if this approach is safe for you. Intermittent fasting is not recommended for children under age 18, people who are pregnant or nursing, or those with existing eating disorders.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Mark Gurarie
Mark Gurarie is a freelance writer, editor, and adjunct lecturer of writing composition at George Washington University.