If you're trying to avoid eating genetically engineered food, good luck. An estimated 75 percent of processed food on supermarket shelves contains at least one genetically engineered ingredient, but it’s not labeled.

The safety of genetically modified food has not been studied over the long term, which is why some consider it one of the largest uncontrolled experiments in modern history.

The good news, says Andrew Kimbrell, in "Your Right to Know: Genetic Engineering and The Secret Changes in Your Food" (Earth Aware, $24.95), is that it’s pretty easy to avoid biotech foods if you eat whole foods, including fruits, vegetables, rice wheat and other grains and beans.

And so far, genetically engineered animals are not commercialized.

But four widely used crops-corn, soy canola and cotton-have been genetically altered and they’re in the majority of packaged food in the supermarket, according to Kimbrall, the executive director for the Center for Food Safety, a consumer watchdog group.

Most GE soy and corn becomes animal feed while the rest is incorporated into processed foods, Kimbrall says. That means the best thing you can do is avoid processed food and eat organic.

Here are some other tips from Kimbrell’s book, which includes a removable pocket shopper’s guide and lists GE-free brands.

If your papaya is grown in Hawaii, it could be genetically engineered. Look for papaya from countries like Brazil and Mexico and areas of the Caribbean where GE varieties are not cultivated.

Remember GE corn includes corn oil, cornmeal, cornstarch and corn syrup. GE soy includes soybean oil, soy flour, soy protein and soy lecithin.

Farm grown fish (trout, catfish, salmon) can be raised on genetically engineered feed. Look for wild rather than farmed.

To avoid GE corn syrup, which is often used as a sweetener in products like yogurt, look for foods sweetened with sugar, natural fruit, honey or pure maple syrup.

Teething crackers and biscuits can contain GE-grown corn syrup and soy lecithin.

The top ten children's food containing GE ingredients are: hot dogs, macaroni and cheese, cereal chips, tomato sauce, French fries, ice cream, soda, peanut better and granola bars.