It may seem counter-intuitive, but a lot of food products that are touted as "diet-friendly" do more damage to your health. In most cases, they actually do the opposite of what a diet should do - they make you fatter. Here are some of the more notorious ones:
People usually recommend yogurt as a dessert for people on a diet, citing it as a good replacement for Ice Cream due to its lack of fat. However, you shouldn't just go around eating every yogurt you can find without checking its ingredients. Most flavored yogurts have flavorings that contain the same amount of fat and sugar as a jelly donut. It is best if you stick to plain yogurt if you want to maintain a healthy diet.
Reduced Fat Peanut Butter
People just see the words "reduced" and "fat" and think that this type of peanut butter is better than the regular one, but it's really worse if you're dieting due to a couple of reasons; first is that fat is actually one of the things that make you feel full. With reduced fat, you tend to consume more just to be satisfied. Second, and more importantly - reduced fat peanut butter would taste bland if the manufacturers don't use a simple component: sugar. This means a "reduced fat" peanut butter actually has the same amount of total calories, but has twice the amount of carbohydrates as regular peanut butter.
People normally assume that sushi is an ideal diet food, since Japanese cuisine has a reputation for being dependent on raw unprocessed food and seafood, but sushi is one of the many exceptions since a single piece can actually pack more than 500 calories, especially the ones that include cheese, spicy mayo, and tempura (which means deep fried.)
Another mistake made by people who try so hard to avoid the usual suspects that they run straight into the arms of another culprit. Just because turkey burger isn't beef doesn't mean it's healthy. An average restaurant order of turkey burger can actually contain 30 grams of fat and 600 calories without even counting the bun and toppings. If you're craving a burger but don't want to ruin your diet, stick to veggieburgers.
Out of all the food listed here, protein bars is actually the most dangerous. People on a diet sometimes use protein bars thinking that it's going to be a good snack replacement. They see gym regulars with fat-free, toned bodies eat protein bars, so it has to be healthy, right? WRONG. Protein bars actually contain twice as much fat and carbohydrates as a regular chocolate brownie. The reason those gym people eat protein bars is that they burn a lot of energy. If your daily activities does not include high impact sports or bodybuilding, protein bars are a sure fire way to gain excess flabs.
At the end of the day, people tend to miss the forest for the trees when it comes to maintaining their fitness and health. They focus so much on curtailing their diet that they end up forgetting that no amount of diet will ever work if you don't support it with a good exercise regimen. One cannot work without the other - if you want to be fit, you need to exercise, but if you want to maintain a regular exercise schedule, you need energy coming from a full, balanced meal.