The Allium family of vegetables, which includes onions, garlic, leeks, shallots, chives, and scallions add more than just flavor to your diet, they also add anti-cancer, anti-inflammatory, and antioxidant compounds.
Epidemiological studies have found that increased consumption of Allium vegetables is associated with lower risk of gastric and prostate cancers, and this is thought to be due to their organosulfur compounds, which are released when the vegetables are chopped, crushed, or chewed. These compounds prevent the development of cancers by detoxifying carcinogens, halting cancer cell growth, and preventing tumors from obtaining a blood supply.
Research suggests that the organosulfur compounds in Allium family members may also have anti-inflammatory actions that protect against osteoarthritis. Osteoarthritis is characterized by painful degradation of the cartilage in the joints of the knees, hands, hips, back, and/or neck. Osteoarthritis is a common chronic condition among middle-aged and elderly persons, a progressive disease affecting nearly 27 million Americans. It is the most common cause of disability in the U.S. 
Excess weight is a risk factor for osteoarthritis (particularly in the knee), and scientists hypothesized that in addition to mechanical pressure on the joints in overweight individuals, a diet low in micronutrients may also contribute to the progression of osteoarthritis. Oxidative stress is known to contribute to osteoarthritis by damaging cartilage, and levels of endogenous antioxidants are suppressed in the fluid of arthritic joints compared to joints with intact cartilage.  Dietary antioxidants are thought to be protective against osteoarthritis, but other micronutrients have not yet been studied.
Dietary patterns and osteoarthritis were assessed in a study of 1086 women. After adjustment for age, body mass index, and physical activity, the ‘fruit and vegetable’ dietary pattern, which was characterized by frequent intake of fruit, Allium vegetables, and cruciferous vegetables and low intake of fried potatoes, was protective for hip osteoarthritis. Two specific food groups also had strong beneficial effects: non-citrus fruits and Allium vegetables.
To investigate a potential mechanism by which Allium vegetables might protect the joints from cartilage damage, researchers then tested diallyl disulphide (DADS; an organosulfur compound) for its effects on inflammation-induced cartilage damage in vitro. DADS suppressed the expression of matrix metalloproteinases (MMPs) – MMPs are elevated in response to inflammatory signals and contribute to the cartilage degradation characteristic of osteoarthritis. These results suggest that organosulfur compounds in Allium vegetables can help to prevent or halt the progression of osteoarthritis.
DADS is just one of many phytochemicals present in Allium vegetables – when we eat these vegetables, thousands of organosulfur compounds, antioxidants, and other micronutrients work together to prevent disease. And when we use garlic and onion to flavor a dish of greens, beans, and mushrooms, the additive nutritional benefits that we receive are remarkable. A nutritarian dietary approach is designed to maximize anti-cancer and disease-protective benefits. If you choose otherwise, eat at your own risk.
1. Powolny, A. and S. Singh, Multitargeted prevention and therapy of cancer by diallyl trisulfide and related Allium vegetable-derived organosulfur compounds. Cancer Letters, 2008. 269(2): p. 305-314.
2. Arthritis Foundation: Osteoarthritis Fact Sheet. 2008.
3. Henrotin, Y. and B. Kurz, Antioxidant to treat osteoarthritis: dream or reality? Curr Drug Targets, 2007. 8(2): p. 347-57.
4. Regan, E.A., R.P. Bowler, and J.D. Crapo, Joint fluid antioxidants are decreased in osteoarthritic joints compared to joints with macroscopically intact cartilage and subacute injury. Osteoarthritis Cartilage, 2008. 16(4): p. 515-21.
5. Williams, F.M., et al., Dietary garlic and hip osteoarthritis: evidence of a protective effect and putative mechanism of action. BMC Musculoskelet Disord, 2010. 11(1): p. 280.