When polled only about one-quarter of Americans report having eaten genetically modified food. However, if you randomly pick an item 
off your grocery store’s shelves, you have a 70 percent chance of picking a food with genetically modified (GM) ingredients. This is because at least seven out of every 10 items have been genetically modified.
If more Americans were aware of this fact, the polls would certainly turn out differently, but Americans are kept largely in the dark about GM products, and most are not aware they are eating these foods because there are no labeling requirements for GM foods. This, despite the fact that there have been no studies done with humans to show what happens when genetically modified foods are consumed, and an ABC News poll (PDF) found that 92 percent of Americans want mandatory labels on GM foods.
Even more concerning is the fact that genetically modified organisms are not easily contained. The Washington Post reported "techniques for confining genetically engineered ... organisms are still in their infancy, and far more work needs to be done to make sure the new products do not taint the food supply or wipe out important species." As a consumer, one way you can voice your resistance to these widely untested, experimental organisms is by not purchasing GM products, a task that is not easy to achieve when you consider the extent to which GM products have already saturated the American market.
There are, however, several ways to reduce your chances of eating GM foods--if you know where to look.
Buy Organic
Buying organic is currently the best way to ensure that your food has not been genetically modified. By definition, food that is certified organic must be:
Free from all GM organisms
Produced without artificial pesticides and fertilizers
From an animal reared without the routine use of antibiotics, growth promoters or other drugs
However, GM crops are becoming more and more prevalent, and the spread of GM seeds and pollen is a major concern. Even organic products may be contaminated with traces of GM elements that have been spread by wind or insects such as bees.
Read Labels
GM soybeans and corn make up the largest portion of genetically engineered crops. When looking at a product label, if any of the following ingredients are listed there’s a good chance it has come from GM corn or soy (unless it’s listed as organic):
Corn Derivatives
corn flour and meal
fructose and fructose syrup(unless specified non-corn)
corn syrup
malt
baking powder(corn starch is the usual filler)
malt syrup
malt extract
monosodium glutamate
maltodextrin
sorbitol
mono- and diglycerides
starch
food starch
modified food starch
confectioner's sugar
dextrin
vitamins that do not state"corn-free"
Soy Derivatives
most miso
soy sauce
tamari
textured vegetable protein(usually soy)
teriyaki marinades
tofu
soy beverages
soy protein isolateor protein isolate
tempeh
shoyu
lecithin or soy lecithin
many non-stick spraysrely on soy lecithin
bread
pastry
margarine
Mayonnaise and salad dressings also may include lecithin
As you can see, there are many products that may contain GM soy or corn derivatives (or GM vegetable oil). Some of these products include:
infant formula
salad dressing
bread
cereal
hamburgers and hotdogs
margarine
mayonnaise
crackers
cookies
chocolate
candy
fried food
chips
veggie burgers
meat substitutes
ice cream
frozen yogurt
tofu
tamari
soy sauce
soy cheese
tomato sauce
protein powder
baking powder
alcohol
vanilla
powdered sugar
peanut butter
enriched flour and pasta
Non-food items include cosmetics, soaps, detergents, shampoo, and bubble bath.
Aside from corn and soy, other GM foods grown in the United States include cotton, canola, squash and papaya.
Look at Produce Stickers
Those little stickers on fruit and vegetables contain different PLU codes depending on whether the fruit was conventionally grown, organically grown or genetically engineered. The PLU code for conventionally grown fruit consists of four numbers, organically grown fruit five numbers prefaced by the number 9, and GM fruit five numbers prefaced by the number 8.
For example:
Conventionally grown PLU: 1022
Organically grown PLU: 91022
Genetically modified PLU: 81022
In terms of fruit, another strategy is to avoid hybrid varieties, which are fruits that have been altered by humans. Typically hybrid fruits contain more sugar than regular varieties so they taste sweeter and can be picked out because generally they don't contain seeds (seedless watermelon, seedless grapes, etc.). Although there are also seeded hybrid varieties, avoiding seedless fruits is one of the more prominent ways to avoid hybrid fruits.
Avoid Processed Foods
About 70 percent of all processed foods contain genetically modified ingredients, and the food manufacturers themselves often don’t know for sure whether their products contain GM elements. There are many reasons why processed foods are not optimal for your health--for instance they often contain trans fat, acrylamide and little nutritional value--so avoiding them will not only help you to cut back on the amount of GM foods you are consuming, but will also boost your health.
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Seeds of Doubt
Genetically Modified Crops Are Contaminating Your Food
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Genetically Modified Crops Are Contaminating Your Food
United States Grows More GM Crops Than Any Other Country
Prominent Scientists Form Group to Counter GM Food
Europeans More Resistant to Genetically Modified Foods
Genetically Modified Foods, Inc.
Even Mice Don't Like Genetically Modified Food
GM Crops Raise Price of Organic Food