For some, they’ve switched to all diet food, or gone fat-free on everything, but can’t seem to get to a healthier weight.

There are reasons why so-called “diet foods” aren’t always so diet.

It’s a familiar refrain in his office.

“What we find is a lot of patients who say, we don’t understand, we switched to all diet foods and we’re still not losing weight,” Dr. Goutham Rao said.

Of course, the dizzying array of choices can make it confusing.

Some people are choosing to go with light-fat alternatives, but watch out for the substitutions that make a food low fat.

“To either improve the taste or to improve the texture, they’ll substitute sodium or carbohydrate for fat,” Dr. Donald Kushner said.

One example of this is with peanut butter.

“For 25 percent reduction in the fat content, they increased the sodium and they increased the sugar content,” Dr. Rao said.

Diet snacks are another culprit.

“Often people will compensate for the fact that something’s a diet food by eating twice as much. The classic example is SnackWells cookies. They might be lower in fat, but they’re high in sugar, and people eat far more of them,” Dr. Rao said.

Another issue is labeling. Don’t get fooled into thinking it’s diet just because it says low-fat.

“They will package it in such a way that it suggests it is low in fat, which might be appealing to some people, but that’s not a food that’s typically high in fat to begin with, so you’re not accomplishing anything by choosing the low fat,” Dr. Kushner said.

When it comes to fast food, salad may seem more slimming, but there’s a catch.

“The chicken Caesar salad at McDonald’s are rather large. So, it’s the total calories people need to pay attention to,” Dr. Rao said.

Drinks can also be deceptive.

“It’s energy drinks, it’s fruit drinks, it’s fruit juices, it’s flavored milk like chocolate milk, it’s milk shakes, it’s sports drinks as well. And some of these flavored water, things of that sort, actually do have calories in them. And we always recommend that all people avoid them completely,” Dr. Rao said.

By and large, it’s not about choosing diet products, but rather controlling portions.

“It’s okay to have the regular food, but just make sure you reduce the portion size. Have half as much as you normally will. Drink a big glass of water, wait 10 minutes and see if you really are hungry again,” Dr. Rao said.

“You have to help people make gradual transitions. You may not expect them to make a change all of a sudden, but if they can make better choices in a total day’s worth of food, then in the long run they can be more capable of making those changes,” Dr. Kushner said.

The doctors stress looking at the label on the back of food products, not just what’s on the front. The back label has the important information about proper serving size as well as how much fat, sodium and sugar you’ll be eating.