Can Onions Lower My Cholesterol?

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.