Having a protein smoothie today as part of your weight loss regimen? Well here’s some food for thought. While you’re very likely to lose weight that way, the cause of the weight loss might not be what you think.

High-protein meal replacements such as shakes, sport drinks and food bars have become a routine for many people trying to lose or control weight.

And it works.

Lots of research backs this up and lots of people have success stories to share. Protein gets much of the credit. Researchers aren’t sure exactly how the results come about, though. And it might be something rather unproteiny that’s causing excess weight to melt away.

For example, a Cornell University paper in the journal Appetite recently showed that substituting a meal with high-fiber breakfast cereal was just as effective as protein meal replacements for reducing weight.

It’s likely that the weight loss comes from the mere fact that the protein drink or bar has fewer calories than the meal it’s replacing.

The Cornell researchers took a group of brave volunteers and replaced one of their meals a day, not with a protein supplement, but with another meal — just a smaller one. That was enough to reduce daily caloric intake and lead to significant amounts of weight loss.

Now, if you want, you could make your smaller meal a gooey, sugary, chocolaty chocolate bar — that certainly might reduce caloric intake. But, to paraphrase George Orwell, not all calories are created equal, and some are definitely better than others. Nutrient-dense foods such as fruits, nuts, veggies and whole grains are healthier than so-called empty calories from processed foods, such as soft drinks and sugary pastries.

So in the end, it’s not just about counting calories, but making sure you get a good nutritional bang for your calorie buck.