Could adding some more sautéed onions to your marinara sauce or adding some diced onions to your salad help lower your cholesterol? Maybe.

Onions are known for their culinary benefits, but they may also benefit your health. Research indicates that onions may even help improve cholesterol levels.

What the Research Says

Onions are strong in flavor and high in polyphenolic compounds called flavonoids. Flavonoids may have:

  • anti-inflammatory abilities
  • antioxidants
  • anticancer abilities
  • antiproliferative abilities, or the ability to stop cell growth

Studies also suggest that onions may help improve cholesterol levels.

In one study, flavonoids in onions reduced the low-density lipoprotein (LDL), or “bad” cholesterol in obese people at risk of cardiovascular disease. The researchers attributed this to the specific flavonoid quercetin, an antioxidant found in onions and other fruits and vegetables. High-density lipoprotein (HDL), or “good” cholesterol, levels were not affected.

Another study looked at the effect of onion extract on cholesterol in rats. The researchers noted a significant decrease in cholesterol levels, though triglyceride levels remained unchanged. Some of the rats were given onion extract and zinc sulfate, while others were only given onion extract or zinc sulfate. Better results were seen among the rats that were given a combination of onion extract and zinc sulfate.

Red onions may also benefit cholesterol levels. In a study published in Food and Function, male hamsters were fed a high-cholesterol diet. Some of the rats’ diet was supplemented with red onion powder. The rats that received the red onion powder experienced lower LDL cholesterol levels and maintained high HDL cholesterol levels. The research was the first of its kind to use red onions.

Onions, Diabetes, and Cholesterol

People with diabetes have an increased risk for cardiovascular disease and stroke. Diabetes often lowers HDL cholesterol, and raises LDL cholesterol and triglycerides. It’s important for people with diabetes to keep their cholesterol in check.

One study examined the effects of combining the diabetes drug metformin (Glumetza, Glucophage, Fortamet, Riomet) and onion extract. Rats with diabetes were given this combination. Researchers saw a reduction in blood glucose and total cholesterol levels. Despite the encouraging results, researchers are unsure how onion extract helps reduce cholesterol levels and why it increased hunger and feeding in rats without diabetes. Many of the studies have also only examined the effects of onion on cholesterol in animals. There have been limited studies in humans. More research is needed.

Raw vs. Cooked 

Most of the research on onions has been done using raw onions or concentrated onion extracts. It’s unclear how the nutrients in onions are impacted when onions are cooked over high heat.

Quercetin levels aren’t altered when onions are simmered. Instead, this antioxidant is transferred into the cooking water or other liquid. As a result, it may be best to consume onions raw, cook them in a liquid, or sauté them over low heat.

Flavonoids are highest in the outer layers of an onion. To retain as many nutrients as possible, be careful to only peel the onion’s thin, papery layer and leave its fleshy layers intact.

Nutrition

When it comes to nutrition, not all onions are created equal. A study published in the Journal of Agricultural and Food Chemistry compared the nutrient value of 10 varieties of onions. Among the varieties tested, shallots were found to contain the highest phenolic content and antioxidant activity. The Western yellow onion topped the list for highest flavonoid content.

Precautions

Most people tolerate onions well when consumed in small amounts. Although rare, some people may have an allergic reaction to onions. Some drugs may also interact with onions. You should use caution if you take any of the following medications:

  • aspirin
  • lithium
  • antidiabetes drugs
  • anticoagulant or antiplatelet drugs
  • medications that affect the liver, such as acetaminophen, chlorzoxazone, ethanol, theophylline, and some anesthetics

Talk to your doctor if you take any of these drugs on a regular basis.

Supplements

Onion supplements may be an option if you simply can’t stand the pungent taste or smell of onions. A standard dosage of onion extract has not yet been established. Taking onion in doses higher than typical food amounts is not advised unless under your doctor’s supervision. In addition, make sure you purchase onion supplements from a trusted source and follow label instructions exactly.

The Takeaway

Research indicates that onions may help reduce cholesterol. More studies are needed, though, to figure out exactly how onions impact cholesterol metabolism. In the meantime, it’s easy to incorporate onions into your diet. Try adding them to any of the following:

  • sandwiches
  • casseroles
  • salads
  • soups
  • chutneys
  • stir fry
  • salsas
  • curries

The next time you cut an onion, smile through your tears, because you’ll be doing something positive for your health.

Looking for some healthy onion recipes? Make Healthline’s grilled onion salad for your next backyard barbecue, or try this South Indian recipe for oats and onion uttapam