Ankylosing spondylitis is a chronic inflammatory disease and type of arthritis. It usually causes pain, stiffness, and reduced mobility in the spine but can affect other joints too.

Although there is no cure for ankylosing spondylitis (AS), early diagnosis and treatment, including dietary changes, can help manage symptoms and reduce the risk of complications.

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Maintaining a healthy weight and eating an anti-inflammatory diet may help to reduce the risk of complications with AS.

While there is no specific diet for AS, certain foods can help people with the condition. Different foods can affect a person's weight, and they can also play a role in inflammation.

AS and weight management

Maintaining a healthy weight is important for those with AS, as excess weight places stress on the bones and joints of the body, which can make symptoms worse.

Being overweight is also a risk factor for the development of osteoarthritis.

Diet and inflammation

An anti-inflammatory diet may help reduce inflammation in the body. This type of diet has similarities to a Mediterranean diet and is recommended by the Arthritis Foundation and the Cancer Treatment Centers of America.

People with AS may find the following foods and nutrients help to ease symptoms:

Omega-3 fatty acids

One limited study found that omega-3 supplements reduced disease activity in people with AS. A 2012 review of research indicates that a diet high in these essential fats has a consistent but modest effect on the joint inflammation associated with rheumatoid arthritis, which is another type of inflammatory arthritis.

Omega-3 fats are found in:

  • chia seeds
  • fatty fish, such as salmon, sardines, and tuna
  • flaxseeds
  • flaxseed oil
  • walnuts

Fruits and vegetables

Eating a variety of fruits and vegetables each day ensures a high intake of many of the vitamins and minerals necessary for overall health. These foods are also low in calories and high in fiber.

The National Ankylosing Spondylitis Society (NASS) in the United Kingdom recommend eating fruits and vegetables of all different colors, as these contain an array of antioxidant compounds that protect against disease.

Whole grains

Whole grains, such as brown rice, corn, quinoa, buckwheat, and oatmeal, are high in fiber and nutrients and may also help lower inflammation.

However, some people may find gluten-containing grains, such as wheat, rye, and barley, trigger their symptoms.

Calcium-rich foods

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Calcium helps bones to stay strong, so eating a calcium-rich diet with AS is recommended.

AS leads to weakened bones, which is why calcium-rich foods are so important. Food sources high in calcium include:

  • dark leafy greens, such as watercress and kale
  • broccoli
  • Chinese cabbage
  • low-fat dairy products
  • fortified plant milks
  • almonds
  • canned sardines with bones
  • fortified tofu
  • fortified cereals

Sources of vitamin D

Vitamin D enables the body to use calcium and is essential for healthy bones. Though normal vitamin D levels ranges from 30 to 100 milligrams per deciliter (mg/dL), research shows that a level of more than 50 mg/dL is more therapeautic and protective against disease.

A 2015 review of research reports that higher levels of vitamin D decrease the risk of developing AS. The vitamin also reduces symptoms in people who already have the condition.

The body gets vitamin D through sun exposure and foods such as:

  • fish and seafood
  • egg yolk
  • cod liver oil
  • fortified foods, such as juices, cereals, dairy, plant-based milk, and tofu

Herbs and spices

Certain herbs and spices are thought to be anti-inflammatory, including:

Garlic: Some compounds in garlic exhibit anti-inflammatory and antimicrobial properties.

Ginger: Considered anti-inflammatory for centuries, recent research has provided scientific evidence to support this.

Turmeric: One of the main components is curcumin, a compound which has been shown to reduce inflammation.

Foods that cause inflammation may make the symptoms of AS worse. These include:

Sugar

Sugar and refined foods can lead to inflammation in the body. So, people with AS should reduce the number of sugary foods they eat, such as desserts, candy, pastries, sodas, and juices.

Salt and high-sodium foods

In 2013, researchers found that adding salt to the diet of animals caused the body to produce an inflammatory cell, which is associated with autoimmune diseases, such as AS.

While a low-sodium diet cannot reverse AS, reducing salt intake is a good idea to help manage the condition.

Red meat

Red meat contains certain chemicals and saturated fats, which can aggravate inflammation. Eating less or no red meat may help reduce symptoms of AS.

High-fat foods

The Arthritis Foundation recommend limiting types of fat which cause inflammation, including saturated fats and omega-6 fatty acids.

Foods that contain saturated fat include:

  • pizza
  • red meat
  • cheese and full-fat dairy products
  • processed foods

Omega-6 fats, while essential in small quantities, are consumed too frequently in the standard American diet.

Foods that contain omega-6 fats include:

  • vegetable oils, including corn, safflower, sunflower, and soy
  • mayonnaise
  • salad dressings
  • pastries
  • processed foods

Trans fats found in processed foods should be avoided.

Starch

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The London AS Diet may be recommended, as reducing starch in the diet may help to reduce the symptoms of AS.

A low-starch diet known as the London AS Diet is often recommended for people with AS. The theory is that some types of gut bacteria trigger AS, and starch feeds these bacteria. Some research has found the diet helps reduce symptoms of AS.

Furthermore, a diet high in refined sugars and starches, with low levels of whole grains and vegetables, has been found to lead to more deaths due to inflammatory disease.

The London AS Diet involves eating less:

  • bread and pastries
  • rice
  • potatoes
  • pasta

It recommends eating more:

  • fruit
  • vegetables
  • nuts and seeds
  • eggs
  • fish
  • lean meat
  • low-fat dairy

However, responses to the low-starch diet are mixed. The Spondylitis Association of America and the National Ankylosing Spondylitis Society in the UK do not promote or oppose the diet.

Wheat and gluten

Gluten-containing grains, such as wheat, rye, and barley are known to contribute to inflammation in some people.

A gluten-free diet is helpful for some people with rheumatoid arthritis and may be beneficial for those with AS.

Alcohol

The relationship between alcohol and rheumatic diseases, such as rheumatoid arthritis, is not always clear. However, people with AS, should limit alcohol intake or completely avoid it.

Heavy alcohol use is known to affect bone health and increase the risk of osteoporosis. Furthermore, alcohol may interact with AS medications and can inhibit nutrient absorption.

Other food triggers

Foods that trigger pain and other symptoms of AS vary from person to person. Keeping a food diary for a month can help individuals pinpoint any foods that may make their symptoms worse.

Certain diets may aggravate the symptoms of AS, including those high in alfalfa, copper, or zinc. Low-calorie, low-fat, and low-protein diets may not provide enough nutrients to support the immune systems of people with AS.

AS is linked to inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis.

Dietary changes can improve symptoms of these diseases. For example, research on AS and Crohn's disease suggests that eating less starch can have a beneficial effect on the symptoms of both, especially when combined with medical therapies.

Other recommendations for people with IBD might include:

  • reducing intake of high-fat foods
  • limiting or avoid alcohol consumption
  • cutting back on dairy products

In addition, an anti-inflammatory diet may help alleviate symptoms of IBD.

Dietary supplements are often recommended for people with AS. However, some supplements can be of poor quality and are not readily absorbed by the body. Others may not do what they claim.

Some of the supplements commonly recommended for AS have no proven benefits for the condition. For example, the group MOVE muscle, bone and joint health advise that, although glucosamine and chondroitin are popular supplements, there is no evidence that they are effective for AS.

Probiotic intake may also prove to be helpful for AS since the Klebsiella bacteria was recently found to be associated with AS.

Making dietary changes to manage symptoms of AS is a good strategy, especially when used with medication or other treatment recommended by a doctor.

However, to ensure adequate nutrient intake, and as certain foods and supplements can interact with medication, discussing dietary changes with a doctor and dietitian is advised.