In the past few years, researchers have studied whether eating certain foods actually prevents disease. Scientists have begun to identify thousands of natural chemicals in foods that seem to have preventative powers. These aren't just vitamins and minerals, they are phytochemicals.

Below are 6 foods that pack a nutritional punch. When used correctly they may have the power to prevent all kinds of serious ailments, including heart disease, diabetes and even cancer.

1. Fiber:Fiber helps to lower cholesterol, reducing risk factors for cardiovascular disease. Researchers at the University of California have said that fiber also reduces the risk factors for colon cancer and breast cancer. Fiber also helps control blood sugar levels, which is important for diabetics. Lastly, diets high in fiber help to keep you feeling full on few calories which will lead to weight loss.

2. Tomatoes:Tomatoes are high in lycopene- which is one of the most powerful antioxidants. Lycopene mops up free radicals thus reducing the risk for prostate cancer. Lycopene is best released from cooking tomatoes, so ketchup and tomato sauces are great sources. Tomatoes are also a great source of vitamin C.

3. Salmon:Salmon has lots of omega- 3 fatty acids which help the heart. Omega- 3s prevent platelets in the blood from clumping together and sticking to arterial walls in the form of plaque. They also drive down triglycerides and LDL cholesterol. Researchers suspect that omega- 3's may block the production of inflammatory substances linked to arthritis and lupus and may even help fight against Alzheimer's. That's because omega 3's interact with the fatty layers that surround brain cells and may help protect them.

4. Spinach: This vegetable is oaded with iron and folate. Folate lowers blood levels of homocysteine, an amino acid that irritates blood vessels and is linked to heart disease. Spinach also contains two phytochemicals that ward off macular degeneration, a leading cause of blindness. One cup has 41 calories, which means you don't have to worry about excess calories.

5. Blueberries:Out of all fruits and vegetables blueberries have the most antioxidants per serving. Blueberries contain a phytochemical called anthocyanins that reduce risk factors for cancer and cardiovascular disease and may boost brain power as well. In a recent study, rats were fed blueberry extract for 9 weeks. Those that were fed the extract performed better as tasks such as navigating mazes and memory tests. Another blueberry benefit, like cranberries, they seem to fight urinary tract infections.

6. Pistachios: They are loaded with fat and can be salty but these filling little snack foods are nutritional powerhouses. Nuts are high in monounsaturated and polyunsaturated fats, which help to lower triglycerides and LDL cholesterol (bad cholesterol) while raising HDL levels(good cholesterol), thus reducing the risk factors for heart disease. Pistachios are also a good source of Vitamin E which is a potent antioxidant that may help ward off cancer. The downside? At about 160 calories per ounce, they are a sure ticket to the fat farm. Eat them by the handful, not bowlful.

Tanya Zuckerbrot, MS, RD is a nutritionist and founder of Skinnyandthecity.com. She is also the creator of The F-Factor DietaC/, an innovative nutritional program she has used for more than ten years to provide hundreds of her clients with all the tools they need to achieve easy weight loss and maintenance, improved health and well-being. For more information log onto