So found a study published in the current edition of the Journal of the American Dietetic Assn, http://www.eatright.org/Media/content.aspx?id=4294967696. Researchers from Tufts University took commercially prepared foods — both prepackaged and from restaurants — and analyzed them in a bomb calorimeter. The measured energy values of 10 frozen meals purchased from supermarkets averaged 8 percent more than originally stated, and foods from 29 restaurants (both fast-food and sit-down venues) were on average 18 percent more than reported.

That hidden — and unwelcome — extra can fool dieters who don't have the time to cook their own meals into thinking they're cutting their caloric intake.

It certainly undermined the efforts of Susan B. Roberts, lead author on the study. The Energy Metabolism Laboratory director said she originally conceived of the idea for the experiment after designing two diets — one that required home-cooked meals, and another that did not. Roberts tested the diets out on herself, and her frustration quickly began to mount. In her home cooked-meal diet, she had lost weight consistently and on target. The no-cook regimen, however, was another matter.

"I wasn't losing any weight," Roberts explained in an interview. "This was ridiculous. I came into the lab one day and thought, something's not adding up — I think there's more calories in these foods than there should be."

Roberts put hr theory to the test. The results? A Lean Cuisine shrimp and angel hair pasta label says it's 220 calories (which works out to 250 calories of gross energy, the study calculates). The Tufts team pegged gross energy at 319. Denny's dry toast lists 92 calories (97 kcal of gross energy). Instead, it let off a whopping 283 calories.

The discrepancies were a little less extreme than those in the Pirate's Booty scandal back in 2002, when a suspicious Good Housekeeping (http://www.goodhousekeeping.com/product-testing/ghri-test-kitchen/snack-scandals?click=main—sr ) employee tested the apparently low-fat snack (label: 2.5 grams of fat) and found it had 8.5 grams, more than three times the stated amount. And to be fair, some foods came in under caloric value (a serving of Domino's thin crust cheese pizza had 141 calories, 33 percent less than expected). But why did most foods seem to err in excess? Roberts said it was likely because "package manufacturers are just playing it safe."

"The FDA regulations are much more punitive, much more stringent on underproviding than overproviding," the scientist said. "It's an old style mentality: 'People need to be given what they pay for.'"

Roberts' advice to dieters? Don't starve yourself — just know what you put into your body. "If you want to lose 10 pounds, you can do it with food. Food is the best way. But by eating at home, you'll have a much easier time."

In any case, if you're eating at a place where "dry toast" earns you 283 calories, you're probably not on the low-calorie bandwagon to begin with.