But before you get mad at the companies, consider this: According to the government, even a 20 percent margin of error is acceptable under current nutrition labeling guidelines. That means a 200-calorie frozen diet dinner, for example, could really be 240 calories — not a huge difference, but definitely something that could sabotage your attempts to lose weight or even maintain it if you're eating a frozen entree several times a week.
Hidden calories add up
Tufts nutrition professor Susan Roberts, lead investigator for the study, calls these "hidden calories" a real problem for those over 50 and watching their weight. "Eating 10 percent more calories than you think is enough to cause 10 or 20 pounds of weight gain a year."
In fact, Roberts got the idea for the study when she couldn't lose weight while researching her own weight-loss book, The Instinct Diet. The book's two-track menus allow dieters to either eat at home or eat restaurant or packaged food. Roberts lost weight on the home-cooked food, but when she was on the eat-out track, "I completely stopped losing weight," she says. Suspicious of the stated calorie counts on the prepared foods she was eating, she decided to test them in Tufts' Energy Metabolism Laboratory.
You can't count on the calorie counts
She and her researchers found about 18 percent more calories than the stated value in foods served at 29 quick-serve and sit-down restaurants, as well as an average of 8 percent more calories than stated in 10 frozen meals purchased from supermarkets. Some of the restaurant dishes had up to twice as many calories as reported — other foods had fewer calories than reported.
Many of the foods were marketed as diet meals. The researchers found that Lean Cuisine shrimp and angel hair pasta, for example, had 28 percent more calories than stated on the package, while Weight Watchers lemon herb chicken piccata had 21 percent more calories than listed. The biggest calorie bonanza: Denny's grits with butter packed a whopping 200 percent more calories than stated, the study reported.
How do they calculate those calories?
In the wake of the study, these companies have reexamined their products' nutritional information and updated the calorie numbers. A prepared statement from Denny's also noted that food is prepared fresh by individual cooks and variations can occur. The company added, "All restaurants are granted a 20 percent leeway in reporting calorie counts because food portioning and ingredients may vary … when a dish is made." A spokesman for Lean Cuisine made a similar point: "Since there is natural variability in ingredients, our label values may vary up to 20 percent."
Margin of error
That 20 percent margin of error is acceptable, according to the U.S. Food and Drug Administration's food labeling regulations. A food is only considered misbranded if the nutrient content "is greater than 20 percent in excess of the value … on the label," says Siobhan DeLancey of FDA's Office of Public Affairs.
The reasons for the 20 percent allowance is because food samples are not always exactly the same. Take a chocolate chip cookie with nuts, for example. "One cookie may contain more chips or walnuts than another, which may change the nutritional profile for that particular cookie," DeLancey wrote in an e-mail. Most importantly, she added, testing methods "are not necessarily 100 percent sensitive."
Lean Cuisine and Weight Watchers respond
Both Lean Cuisine and Weight Watchers also noted that they base their products' nutritional information on "an average value taken from multiple samples in accordance with government regulations," as Weight Watchers' spokesman Tracey Parsons wrote in an e-mail. The Tufts study tested only one sample of food from each company and restaurant.
To test the calorie counts of the sampled foods, Roberts and her researchers blended the food, freeze-dried it and burned the resulting powder to see how much heat it produced — a measure of its energy content, or calories.
What they found, she says, was that many "mixed" foods — such as packaged meals like chicken and pasta or steak and vegetables — contained more calories than their manufacturers stated. She attributes the discrepancies to the fact that manufacturers don't typically have the equipment to test calories; instead, they rely on calorie counts for individual ingredient foods as listed in the government's database.
In mixed foods, she says, the ingredient levels might not be precise, meaning the calorie count numbers are off, too. For example, Roberts and her team tested several frozen meals by Lean Cuisine, Healthy Choice and Weight Watchers and found that some contained more calories than the manufacturers stated on the nutrition label. A few foods were underestimated. Lean Cuisine roasted garlic chicken, for example, had 4 percent fewer calories, the researchers say.
Roberts acknowledges that by testing only one sample, researchers couldn't conclude that these meals are consistently off the mark. And although the calorie differences were slight in many cases, for someone using a daily calorie goal to lose or maintain weight, even slight differences can add up to big effects.
If you're 50 or older — watch out
The bottom line? If you're over 50 and watching your calories, you should assume that the calorie counts in restaurant foods and packaged foods are higher than what is stated on the label or menu, Roberts says.
Cutting back on calories isn't just about staying svelte — research has shown that eating less can help individuals live longer and may even help ward off age-related illnesses.
Other traps for 50-plus men and women
Hidden calories sneak into our diets in other ways, too, says Dee Sandquist, spokesperson for the American Dietetic Association. The main source of calories we don't realize we're eating is large portion sizes, she says.
"After the age of 40, we need fewer calories every decade," she says. "But a lot of people, especially those in their 50s, have not yet reduced portion sizes." As we age, Sandquist says, we have fewer discretionary calories — calories we can consume beyond the number of calories we need to simply maintain our current weight. For most of us, it's about 100 calories per day on average, depending on our activity level and other factors, such as how much lean muscle you have. That 100 calories can equate to the after-dinner cookie we're used to grabbing or the extra sausage link at breakfast.
Controlling our weight as we age is vital, Roberts says, adding that her laboratory is conducting one of three National Institutes of Health-funded studies on whether human calorie restriction improves benchmarks of longevity. Though the results aren't yet in, Roberts says there's no question that avoiding weight gain as we get older is "enormously helpful" in preventing age-related illnesses such as heart disease, type 2 diabetes, high blood pressure and others.
For weight loss, older trumps younger
And, she says, older people tend to do better at losing weight.
"Successful weight loss requires some organization and planning," Roberts says — something with which older adults have a lifetime of experience. Their lives tend to be more settled, she adds, making meal planning and keeping healthy foods in the house easier.
Dara Chadwick writes frequently about health and wellness.