Watermelon
The high liquid content of watermelon, along with the natural sugars and fiber, make it the perfect snack. However, it’s much more than just a snack. Tomatoes are highly touted for their high content of the immune strengthening antioxidant lycopene. The fact is that watermelon actually contains more lycopene (40% actually) than tomatoes. If you bring one home, keep it out even once it’s cut instead of refrigerating it. This may sound strange, but you get the most benefit this way. Room temperature watermelon can continue producing antioxidants for up to two weeks.

Onions
Primarily used for seasoning, onions are high in vitamin C, fiber, folate, and vitamin B-6. They also contain large amounts of quercetin, which can help relieve allergies and has also been known to have anti-cancer effects. Studies have shown that people who eat the most onions can reduce their risk for oral cancer by 84%, colon cancer by 56%, breast cancer by 25% and prostate cancer by 71%. Red onions have the most quercetin, but pink shallots have a wider mix of antioxidants.

Lettuce
Looking at the light green color of most lettuce would generally lead one to believe that it doesn’t have the nutrients of other vegetables, but this is not the case. Iceberg lettuce contains lutein and zeaxanthin, which are carotenoids that reduce the risk of cataracts and age related macular degeneration. Add a salad at the beginning of a meal to get some of these benefits, and you’ll also likely eat fewer overall calories due to feeling more full and satisfied.

Microwave popcorn

Chemicals that can be found in the lining of the bag itself have been linked to human infertility, and in animal testing they have caused various types of cancer including liver, pancreatic, and testicular.  Studies have shown that the process of microwaving can cause these chemicals to vaporize and therefore migrate into your popcorn.

Milk produced with artificial hormones

Some, but not all dairy farmers treat their cattle with growth hormones to increase milk production, and thereby profits.  These hormones can also increase infections and because of that, possibly even pus in the milk.  This also increases production of insulin like hormones in the milk which can contribute to colon, breast, and prostate cancers in humans.

White flour

All of the good nutrients in flour are removed during processing, and then it is bleached with a chemical agent that is very similar to the same bleach you use in cleaning and laundry.  Some vitamins get added in the final processes, and it's passed off as "enriched".  What most people don't know is that this so called "enriched" flour can cause increases in blood sugar that rival refined sugar.

Vegetable oils

For a long time the experts have told us how much healthier and beneficial oils like canola, corn, and soy are.  The problem with this lies in their transformation into cooking oils.  This process includes heavy refinement that can make them oxidized and therefore toxic.  A much healthier option is coconut oil, which does not oxidize.  For higher heats try grapeseed oil, or extra virgin olive oil for light cooking.