Onions contain a number of beneficial nutrients and plant compounds that may help support liver health. This article reviews the evidence on the effects of onions and their compounds on liver health and disease.
Benefits of Onions for the Liver
Onions are low in calories but packed with nutrients. Some of these nutrients may be particularly beneficial for liver health.
Antioxidants
Onions are an excellent source of antioxidants, which help protect your cells from damage caused by unstable molecules called free radicals. Antioxidants may be especially beneficial for liver health, since your liver functions to remove toxins and metabolize medications — processes that generate a lot of free radicals (1).
Specific antioxidants found abundantly in onions include:
- Quercetin: A flavonoid antioxidant thought to have anti-inflammatory and anticancer properties (2).
- Anthocyanins: Pigments with antioxidant effects that may reduce inflammation (3).
- Sulfur compounds: Such as allyl propyl disulfide that have antioxidant and antimicrobial effects (4).
By neutralizing free radicals, these antioxidants may help prevent damage to liver cells caused by everyday toxins and waste products.
Vitamins and minerals
Onions are rich in vitamins and minerals that are essential for liver health:
- B vitamins: Including folate and vitamins B6 and B12. B vitamins help metabolize proteins, fats, and carbs (5).
- Vitamin C: A powerful antioxidant that helps the body synthesize bile and glutathione, your liver’s natural antioxidants (6).
- Potassium: May promote liver enzyme activity and support liver function (7).
- Phosphorus: Involved in energy production and waste removal in the liver (8).
Getting enough of these nutrients promotes the liver’s natural detoxification processes and ability to remove waste products and toxins from your blood.
Prebiotics
Onions contain the prebiotic fiber inulin, which helps nourish beneficial gut bacteria. Animal studies have found that inulin may protect the liver against nonalcoholic fatty liver disease by increasing numbers of beneficial Bifidobacterium bacteria (9).
Since gut health is closely linked to liver health, promoting healthy populations of bacteria through prebiotic fibers like inulin may benefit your liver.
Effects on Liver Health
In addition to their nutritional content, onions and their compounds have specific effects that may benefit liver health and help prevent liver damage and disease.
Protect Against Toxins
Animal studies demonstrate that onions may help protect against liver damage from aflatoxins — toxic compounds produced by molds.
Quercetin seems to be a key compound responsible for this protective effect. One study in mice found that quercetin guarded against liver injury caused by a high dose of aflatoxins (10).
Additionally, quercetin has been shown to reduce damage caused by drugs like acetaminophen (Tylenol). Again in mice, quercetin decreased damage caused by acetaminophen overdose. What’s more, onion extract enhanced the beneficial effects (11).
Similarly, other rodent studies note that onion extract exhibits protective effects against carbon tetrachloride (CCl4), a solvent known to induce liver injury (12, 13).
Overall, components in onions, including flavonoid antioxidants like quercetin, seem to reduce liver damage caused by drugs, toxins, and infectious agents.
May Support Healthy Cholesterol Levels
Eating onions may help support healthy cholesterol levels, which is beneficial for liver health, as fatty liver can develop when there are high levels of fats in the blood.
In one study, rats fed diets high in onion powder over 28 days experienced increased HDL (good) cholesterol levels (14).
Plus, population studies associate higher allium vegetable intake with reduced risk factors for heart disease like high triglyceride levels, which may otherwise contribute to fatty liver (15, 16).
The fiber inulin may also contribute to onions’ beneficial effects on cholesterol levels.
Overall, onions seem to support healthy cholesterol levels, which may promote liver health.
Can Protect Against Liver Cancer
Limited evidence from human studies suggests that eating onions may offer some protection against liver cancer.
One study in over 41,000 men found that greater onion consumption was linked to an estimated 56% lower risk of liver cancer. For every 20 grams of onions eaten per day, liver cancer risk declined by approximately 22% (17).
Similar results were seen in an analysis of over 80,000 women, though the association was not as strong. For the highest onion intake, there was a 27% lower risk of liver cancer in women (18).
However, keep in mind that these were observational studies. Higher onion intake may be a marker for an overall healthier diet and lifestyle in these populations.
Still, coupled with onion’s known antioxidant content and effects in animal studies, this data suggests onions could potentially help lower liver cancer risk in humans.
Onion extracts high in quercetin are considered to have anticancer properties and have been studied for both preventing and treating cancer in animal models (19).
Overall, limited population studies link greater onion intake to lower liver cancer risk. More research is needed to determine if eating onions directly reduces liver cancer risk in humans.
Other Potential Benefits
In addition to the major benefits above, preliminary evidence suggests onions may offer other advantages for liver health:
- Reduce oxidative stress: Quercetin in onions may reduce markers of oxidative damage in people with hepatitis C (20).
- Protect the liver: Saponins in onion may help protect against damage from certain medications in rats (21).
- Support detoxification: Onion extract enhanced antibiotic detoxification processes in mice (22).
However, human research on these specific effects is limited.
Downsides of Onions for Some People
While considered very healthy for most, onions do have some downsides:
- May interact with certain medications that are metabolized by the liver.
- Contain fructans, which may exacerbate symptoms in those with irritable bowel syndrome (IBS).
- Can cause abdominal pain, gas, acid reflux, and bloating in sensitive individuals.
- High in sulfur, which may trigger headaches, asthmatic reactions, or other responses in those with sulfur intolerances.
Additionally, given their impact on liver enzymes, people taking certain medications may need to monitor or limit onion intake. This includes drugs metabolized by the liver’s cytochrome P450 enzymes, such as some blood thinners and antidepressants (23).
Those with IBS or intolerance to sulfur-rich foods may also need to limit their servings of onions to minimize unwanted digestive side effects.
The Bottom Line
Onions provide a range of antioxidants, vitamins, minerals, and prebiotics that may support liver health. They may help protect the liver from damage and disease.
Human studies link greater onion intake to lower risk factors for liver issues like fatty liver and liver cancer. However, it’s unclear if onions directly reduce liver disease risk.
Regardless, onions make a great addition to a healthy, whole food diet. Unless you have an intolerance, there’s little downside to incorporating more onions into your meals.
Aim to eat a variety of allium vegetables like onions, garlic, leeks, and shallots. Pair them with fresh veggies, lean proteins, and healthful fats as part of a balanced diet to maximize the liver and overall health benefits.
Frequently Asked Questions
What are the benefits of onions for the liver?
Onions contain antioxidants, vitamins, minerals, and prebiotics that may support liver health. They may help protect liver cells, aid natural detoxification processes, reduce damage from toxins, and lower risk factors for fatty liver and liver cancer.
Are onions bad for your liver?
No, onions are considered very healthy for the liver. No studies suggest onions are bad for liver health.
That said, onions contain substances that may interact with some medications metabolized by the liver’s cytochrome P450 enzymes. People taking these drugs may need to monitor their onion intake.
Do onions help repair your liver?
There’s limited evidence that onions or onion extracts directly repair or reverse liver damage. However, they provide nutrients that are important for the liver to function optimally and may help lower risk of liver disease.
Can onion juice heal a fatty liver?
There are no studies examining if raw onion juice alone can heal a fatty liver. However, onion’s nutrients and plant compounds may help lower fat buildup in the liver. Onion juice may be used alongside lifestyle changes like diet and exercise modifications to help treat fatty liver.
What food is good for liver repair?
Some foods particularly beneficial for liver health include:
- Coffee
- Olive oil
- Grapefruit
- Prickly pear
- Garlic
- Nuts
- Cruciferous vegetables like broccoli and Brussels sprouts
- Avocado
- Green tea
- Fatty fish like salmon and sardines
Pairing these foods with a diet high in fruits, vegetables, lean proteins, and whole grains supports overall liver function and repair.
Conclusion
Onions provide beneficial nutrients and plant compounds that support liver health. Though human studies are limited, greater onion intake is linked to lower risk of issues like fatty liver and liver cancer.
Incorporate onions into a balanced diet with plenty of whole foods to maximize the health benefits for your liver and body.