Avoid eating a lot of processed foods. Books that are highly critical of the American food industry, including "Fast Food Nation" by Eric Schlosser and Pollan's "The Omnivore's Dilemma," explain how many of these products are manufactured by mixing together a multitude of chemicals. Thousands of foods sold in grocery stores are made this way.
To implement change in eating habits, begin to look at food labels. But instead of focusing on nutritional facts, as Pollen recommends, read the ingredients instead. Is the list long? Does it contain words difficult to pronounce? If the answer is yes, that's a good indication the food was manufactured in a factory.
"But wait, this says it contains more omega-3s!"
According to Pollan, more often than not, to get a food to contain more of any one vitamin or mineral, chemicals get added that compromise the purity of the food in another way. Simply put, avoid any products with labels that make a miracle health claim.
Finally, enjoy the changes you just made. Eat slowly and savor the taste. Our brains don't know our stomachs are full for 20 minutes, so take your time. That way, you're less likely to overeat.