5. Nutrition info It’s difficult enough skirting marketing claims, but what can really get frustrating is when you realize that the government-mandated nutrition label on that box of crackers you’re holding may not be telling you the whole truth. The two things to pay attention to on packaged foods are the serving size and the trans fat listing, says Jayne Hurley, RD, senior nutritionist at the Center for Science in the Public Interest. “Serving sizes are mandated by the FDA,” she says; they aren’t defined by food companies, as most people assume.

The trouble is that serving sizes were defined in the ’70s, based on individuals’ self-reported food consumption habits in FDA interviews, which are often underestimated, says Hurley, and don’t reflect the consumption habits of people today. “Look at a soup can with 2.5 servings,” she says. “Who’s going to divide that can into 2.5 servings?” Unless you’re willing to do the math, she adds, the nutrition information doesn’t reflect what you’re eating.

Another sticky label is the trans fat listing. The FDA allows manufacturers to put “0” if the amount of trans fats per serving is below .5 grams. “That’s a quarter of a day’s worth,” says Hurley, who notes that 2 grams is what health experts suggest is the maximum. “And the manufacturers aren’t breaking the law. It’s perfectly legal.”

To get the real thing: Do a reality check on the serving sizes of the foods you buy: Are you likely to eat all three servings in a single sitting? If needed, bring a calculator (or use the one on your cellphone) to add up how many calories, fat, salt, and so forth, you’re really getting. And read ingredient labels, not nutrition labels, to avoid trans fats. Avoid any product with partially hydrogenated oils listed as an ingredient. “If there’s no partially hydrogenated oil, the trans fat content really is zero.”