Osteoarthritis is the most common form of arthritis in the knee. Medications can help to control symptoms, but diet can also make a difference.

Osteoarthritis (OA) of the knee damages the cartilage in the knee joint. Cartilage is a tissue that acts as a cushion at the ends of bones within joints. This results in pain and mobility problems.

Maintaining a healthy weight is important to alleviate pressure on the knees, but certain substances in foods might also affect the body in a way that could help relieve inflammation and pain.

Read on to find out which foods might benefit people with OA, which ones to avoid, and which ones are unlikely to make a difference.

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Fish oils may help protect the knee joint from damage by OA.

Inflammation happens when the body's immune system reacts to any disease, injury or irritation that it encounters. The symptoms are redness, swelling, and pain.

Inflammation is both a cause and a symptom of OA. Eating foods that contain anti-inflammatory substances might help people with OA.

Certain types of fish are rich in omega-3 fatty acids. These acids help reduce levels of two proteins called the C-reactive protein (CRP) and interleukin-6, which cause inflammation.

Some people with OA have high levels of CRP. This can lead to increased pain and swelling.

Omega-3s help the body respond to inflammation by interfering with certain cells. The omega-3 fatty acids in fish can help stop inflammation before it damages the joints.

According to the Arthritis Foundation, people who regularly eat fish that is high in omega-3s are less likely to develop rheumatoid arthritis (RA). This may also be useful for people with OA.

The Foundation also point out that fish oil supplements could protect joints from cartilage breakdown or reduce its severity.

Eating a 3-to-6 ounce (oz) serving of fish at least four times a week can help reduce OA inflammation and protect the heart.

Fish that are rich in omega-3s include:

  • salmon
  • tuna
  • sardines
  • mackerel

Fish-oil supplements are also available, but eating fish offers greater benefits.

Fruits and vegetables play a major role in a healthful diet, and they contain nutrients that can help people with OA of the knee.

Fiber

Researchers have found that people with OA may have high levels of cholesterol.

The American Heart Association recommend consuming whole grains and other forms of dietary fiber as they appear to improve blood cholesterol levels.

Fiber also helps a person to feel full for longer, and this can help in maintaining a healthy weight.

Anti-oxidants

Antioxidants support the immune system and fight inflammation. There are many types of antioxidants.

Dietitians often recommend berries for their antioxidant content. Examples include blueberries, strawberries, and raspberries. Fresh red and black grapes contain resveratrol and soy products contain isoflavones.

Healthful fats

Avocados are high in anti-inflammatory monounsaturated fat. They are also a good source of vitamin E, which has anti-inflammatory effects. Diets high in these compounds have been linked to a decreased risk of joint damage seen in early OA.

Oleocanthal

Olives and extra virgin olive oil contain oleocanthal. This compound is a natural anti-inflammatory agent that has properties similar to the drug ibuprofen.

Turmeric

Turmeric has long been used in herbal and traditional medicine, and there is a lot of interest in its benefits.

One review of studies found that 100 people with OA who used a turmeric-based drug, Meriva, for 8 months, saw a reduction in pain and other symptoms related to OA. In another study, 50 people who used Meriva for 3 months were able to walk further and had lover CRP levels at the end of the treatment.

Hydration

Watermelon is naturally high in carotenoid beta-cryptoxanthin, a compound that can help reduce the risk of RA.

As watermelon contains a lot of water, it is useful for hydration and water management. It also contains substances that can reduce CRP levels.

Vitamins A, C, and K

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Spinach, broccoli, and other green vegetables provide fiber as well as important minerals and vitamins.

During the production of energy and other processes, the body produces harmful byproducts called free radicals.

These can damage the cells in the body. Free radicals have been linked to inflammation that attacks the joints.

Green leafy vegetables — such as broccoli and spinach — contain vitamins A, C, and K, which are antioxidants.

These help to protect cells from free radical damage. They also contain high levels of calcium, which contributes to bone health.

Sulforaphane and glucosinate

Broccoli and other cruciferous vegetables such as cabbage and Brussels sprouts also contain the natural compound, sulforaphane.

In one animal study, sulforaphane and another compound — glucosinolate — blocked the inflammatory process and slowed down cartilage damage in OA.

Glucosinolate is found in pungent plants like horseradish, mustard, and cabbage.

Vitamin C

Peppers, oranges, and green, leafy vegetables are good sources of vitamin C. This helps preserve bone and it can play a role in protecting cartilage cells.

Contrary to some beliefs, there is no evidence that the acidity in citrus fruits leads to inflammation, but they can provide useful vitamin C.

Grapefruit juice, however, can interact with some medications, so you should check before consuming too much of it.

Some people advise against eating dairy foods, but this is probably helpful only for people with a lactose intolerance.

Low-fat dairy products can offer some benefits for people in OA of the knee.

Sterols and stanols

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Dairy produce can contain useful vitamins for people OA of the knee.

Some foods are fortified with plant-based sterols or stanols.

These may help to reduce cholesterol levels.

Examples of products include fortified milk, fortified spreads, and fortified yogurts.

The person should consume these as part of a diet that is low in saturated fats.

Calcium and vitamin D

Low-fat milk, cheese, and yogurt can also provide vitamin D and calcium, which may help to strengthen the bones.

Scientists have found evidence of low vitamin D levels in people with OA.

Consuming more vitamin D through fortified dairy foods and regular, safe, exposure to sunlight may offer benefits for people with OA.

Many of these nutrients are available as supplements, but doctors usually advise people to get their nutrients from natural foods before using supplements.

According to Harvard Health, glucosamine and chondroitin may help some people with arthritis, although most of the research shows that they do not have any effect for most people.

People should always ask their doctor before using any supplements, because some of them can have adverse effects on some people and they may change the way other medications work.

People with OA of the knee should try to avoid some foods, as they may aggravate the condition further.

Sugar: Apart from contributing to weight gain, sugar can also trigger the release of cells that can increase inflammation. Other foods containing highly refined carbohydrates, such as white bread, may have the same effect.

Salt: Salt can cause cells to attract water, which could aggravate OA. Joint swelling is a common symptom of OA. Consuming too much salt can worsen this swelling. Processed and prepackaged foods often contain high levels of salt.

Transfats and saturated fats: These are common in processed foods and baked goods, but they can trigger inflammation.

MSG: A food additive that often features in oriental foods and soy sauce, monosodium glutamate (MSG) can also be a hidden ingredient in fast foods, soup mixes, and so on. Other additives, such as the sweetener, aspartame, may have a similar effect.

Omega-6 fatty acids: Omega-3 may help people with arthritis, but omega-6 fatty acids — which occur in various types of cooking oil — might boost the body's production of inflammatory chemicals. Examples of oils containing omega-6 include corn and sunflower oils.

Alcohol: The Arthritis Foundation recommends limiting alcohol intake and avoiding smoking. Alcohol may interact with some medications, including pain-relief drugs.

Food sensitivities: Some people have sensitivities to certain foods. Removing potential allergic or sensitive foods through an elimination diet may be a way to improve symptoms.

People have recommended the following for treating the symptoms of arthritis, but there is no evidence to show that they work:

  • gelatin, collagen, and pectin
  • the alkaline diet
  • apple cider vinegar
  • the raw-food diet

Should I avoid solanine?

The nightshade family of vegetables includes tomatoes, potatoes, and peppers. These contain the chemical solanine. Some people believe this chemical can cause arthritis pain, but no studies or research have ever shown this claim to be true.

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Swimming strengthens the body without putting pressure on the knee joint.

A person with OA needs to maintain a healthy weight, because excess weight puts additional strain on the joints. This means more pain, inflammation, and swelling.

Here are some tips to help people maintain a healthy weight.

Satiety: Natural fiber can make people feel fuller for longer, and they may help lower cholesterol or prevent diabetes. Rough oatmeal, whole grains, and fresh fruits and vegetables are all good sources of fiber.

Cooking methods: Opt for baked, grilled, steamed, and some raw foods rather than fried or roasted in oil. Deep-frying adds extra calories and takes away much of the nutritional content.

Exercise: This is important for overall fitness and maintaining a suitable weight. Knee pain may make some exercises more difficult, but simple stretching and other motion exercises can help strengthen the leg muscles, and this will make it easier to walk.

One study found that people with OA who were overweight and lost 10 percent or more of their weight saw improvements in pain and function, especially when they participated in physical activity, too.

While there is not much evidence to suggest that particular foods can benefit people with OA of the knee, it is a good idea overall to:

  • follow a balanced diet and do some physical activity
  • avoid processed and refined foods, as these often contain trans-fats, added sugar and salt, and refined carbohydrates
  • include a wide range of fruits and vegetable as these add fiber and vitamins, some of which are antioxidants, and they may help to reduce inflammation

Learning how to read the nutritional labels can help a person to avoid high levels of salt, sugar, and unhealthful fats.