Along with adding flavor to your food, onions offer many health benefits. They contain plant compounds that may help with blood sugar control, heart health, and immunity.
Onions contain antioxidant compounds, particularly the flavonoid quercetin, which may improve heart health. Research shows that quercetin may lower blood pressure, reduce cholesterol, and improve blood circulation.
In one study, people with slightly high cholesterol who drank 100 milliliters of onion juice saw a drop in total and low-density lipoprotein (LDL) “bad” cholesterol.
Most research has been limited to small studies in people or done in animals. Also, many studies use onion supplements instead of whole onions. More human research is needed.
Quercetin and sulfur compounds found in onions may help regulate blood sugar. They work by improving how the body processes glucose (sugar) and responds to insulin.
A study in people with diabetes showed that eating 100 grams of raw red onion helped the body use and remove sugar from the blood better.
Onions, especially red onions, are a good source of vitamin C.
Vitamin C strengthens your immune system by supporting the production and function of white blood cells. In the body, white blood cells fight off harmful bacteria and viruses that could cause infection or disease.
The sulfur compounds in onions may also support immune health. One study found that these compounds helped improve immune function in people with colorectal cancer.
An older study in perimenopausal and postmenopausal women found that eating onions may improve bone health. Women who ate onions at least once a day were up to 20% less likely to experience a hip fracture compared to those who rarely or never ate them.
A 2024 study in rats with osteoporosis (weak and brittle bones) found that onion flavonoid extract helped improve bone strength and bone density. More human studies are needed to confirm the bone health benefits of onions.
Lab studies suggest that compounds in onions may help prevent the growth of harmful bacteria that cause infection. In one study, quercetin was shown to disrupt bacterial cell walls and prevent the growth of E. coli and Staphylococcus aureus.
Quercetin may also prevent the growth of Helicobacter pylori (H. pylori), a type of bacteria that infects the stomach. H. pylori can increase the risk of peptic ulcers and gastritis (inflammation of the stomach lining).
Onions are a natural source of prebiotics, which feed the good bacteria in your gut and support digestive health. They contain inulin and fructooligosaccharides (FOS), fibers that promote a healthy gut microbiome. These fibers have also been linked to improved digestion, mood, nutrient absorption, and immune function.
Flavonoids and antioxidant compounds in onions can neutralize harmful free radicals before they can damage your body’s cells.
Quercetin may prevent the formation of compounds that cause inflammation. These include leukotrienes, prostaglandins, and histamines. This may help reduce inflammation associated with arthritis and other chronic conditions. More human research is needed.
Quercetin and other flavonoids in onions may block the growth and spread of certain cancer cells.
A 2019 study found that regularly eating allium vegetables, such as onions, leeks, and garlic, may reduce the risk of colorectal cancer by up to 79%. Similarly, another study showed that higher consumption of garlic and onions might lower the risk of breast cancer.
More well-designed human trials are needed to fully understand how onions may help prevent cancer.
When consumed in normal amounts, onions are generally considered safe for most people. However, there are a few things to consider:
- Gas and bloating: Onions are high in FODMAPs, which can cause digestive discomfort in people with irritable bowel syndrome (IBS).
- Allergic reactions: Though very rare, some people may be allergic to onions and could have a reaction when handling or eating them. If you’re allergic to other plants in the Liliaceae family, like garlic, you might also be allergic to onions.
- Medication interactions: In large amounts, onions may have a blood-thinning effect. If you take blood-thinning medications, talk to your doctor before making any major changes to your diet.
Eating onions can also temporarily contribute to bad breath. You can manage bad breath by brushing your teeth, flossing, or using mouthwash after eating onions.
Onions can add depth and flavor to a variety of meals. While raw onions offer health benefits, studies show that baking, grilling, or frying onions may increase their health-protective compounds.
Here are some simple ways to enjoy onions:
- Sauté onions in stir-fries and soups for a flavor boost
- Sprinkle finely chopped onions in salads and sandwiches
- Caramelize onions slowly for a sweet topping on burgers or grain bowls
- Roast onions with other vegetables
- Add sliced onions to tacos or avocado toast
- Blend onions into dressings, dips, and sauces for extra flavor
Onions are a versatile vegetable that can boost the flavor of many dishes. They provide nutrients and beneficial compounds that may help improve your health. While more human research is needed, eating onions regularly as part of a balanced diet may support heart, bone, immune, and gut health.
