Winter is a challenging time of year to eat clean. When gardens stop growing and farmers markets close for the season, locally grown produce is scarce. Add in the lack of daylight and colder weather, and your motivation to eat clean may wane.

Wintertime, however, is when to make health a priority. Your immune system can take a beating during the colder months when people gather indoors and share germs. Regular exercise, plenty of sleep and clean eating boost your immunity to help your body fight back when you're exposed to contagious illnesses. Here are some of the healthiest winter clean-eating contenders.

Eat Orange and Green Fruits and Vegetables

If you're trying to get more greens into your diet, a green superfood powder supplement can help. Luckily, some of the healthiest green vegetables grow in cold weather. Kale, Brussels sprouts and Swiss chard are in this group. Kale prefers cold weather and can even tolerate snow. Likewise, Brussels sprouts withstand freezing conditions. Collard greens are also cold-hardy and reach peak flavor after a frost.

Cold weather causes carrots to convert stored starches into sugars, preventing their water-filled cells from freezing. This produces sweeter-tasting carrots, often called "candy carrots," when harvested after a frost. Clementines grow in the winter, as do grapefruit. Of course, many varieties of winter squash are orange, including butternut squash and pumpkins.

Spice Up Your Diet

Some of the most flavorful foods and spices are known for their antioxidant benefits and immunity support. Adding garlic, onions, cilantro and ginger to your dishes will boost your immune system. Garlic and ginger act as natural blood thinners, helping to lower high blood pressure and cholesterol. Onions can also help lower blood sugar and are an excellent quercetin source, which has antiviral properties. Cilantro also shows promise in lowering blood sugar.

Turmeric, a yellow spice used in traditional Eastern medicines, is an antioxidant and is credited with reducing inflammation and heart disease. Cinnamon, another antioxidant, can lower blood sugar. Sage developed a reputation for its healing properties in the middle ages, and modern research indicates it may help with memory and brain function, especially in people with Alzheimer's disease.

Peppermint is known for reducing nausea. It can also reduce bloating in the abdomen and help with irritable bowel syndrome by relaxing the colon's smooth muscles.

Sip Herbal Tea

On a cold day, a cup of hot tea can be very soothing. As a bonus, it can also be very healthy. Research has established that the flavonoids in tea are rich in health benefits, including heart health.

Green tea is being studied for its possible ability to interfere with the growth of certain types of cancer. It may also boost heart and brain health, reduce stroke risk and some neurological diseases, and burn fat. That's a lot of power packed into one variety of tea.

Other teas have health benefits, too. Black tea may reduce the risk of stroke and guard the lungs against the effects of cigarette smoke. Oolong and Pu-erh teas have shown an ability to lower LDL (bad) cholesterol. Uncured and unfermented white tea appears to have cancer-fighting capabilities.

Curb the Carb Cravings

Comfort foods are what you probably crave most in the winter. They increase our levels of happiness-inducing serotonin, making us want more carbohydrates. Start your day with a protein-packed breakfast to keep energy levels steady throughout the day. Healthy, low-fat snacks can help fight the mid-afternoon carbohydrate cravings.

The temptation to put clean eating on hold for the winter may be substantial. However, sticking to your healthy diet is worth the effort. You'll power through the dark, cold months feeling better, and you may even fight off illnesses. You'll feel good until spring rolls around again.