Fitness apps are all the rage. An explosion of new companies and products want to track your steps and count your calories with the aim of melting that excess blubber. There’s just one problem — most of these apps don’t work. In fact, there is good reason to believe they make us fatter.

They backfire and make us less happy and more flabby for three reasons.

The first reason: they’re based on a pervasive myth. Eat too much or move too little, the thinking goes, and you’ll get fat, right? Well, not exactly.

There’s a ton of evidence that the whole “calories in, calories out” theory is too simplistic. For example, doctors have known for some time that certain medications cause patients to gain or lose weight by changing hormone levels in the body. To most fitness apps, a calorie of high-fructose corn syrup is the same as a calorie of protein despite the fact that science, and our bodies, tells us otherwise. Clearly, a calorie isn’t just a calorie.

The second reason that these fitness trackers fail is that exercise may actually be bad for you. Exercise causes many people to overeat by giving them permission to indulge. The phenomenon is called moral licensing — the psychological tendency to splurge in one area of our life when we’re being good in another.

The phenomenon accounts for why many runners gain weight while training for a race. They expend more calories during their runs, but by rewarding themselves with indulgences throughout their day like an insulin-spiking post-workout “sports drink,” they ultimately negate many of the health benefits of exercise.

There’s another reason people rarely exercise themselves thin. Most fitness apps ignore the fact we work up an appetite.

For roughly 95 percent of the 200,000 years our species has existed, food was relatively hard to come by. Today however, sugar-laden calorie bombs are cheap, delicious, and readily accessible. Whereas our ancestors laboriously cracked nuts with their bare hands and primitive tools or gnashed animal carcasses with their powerful jaws, we sip pre-masticated Mega Mango Smoothies at Jamba Juice (with 52 grams of sugar in the smallest 16 ounce size).

Exercise does us in by making us hungrier throughout the day and since our food is so full of stuff that makes us fat, we become more likely to over-consume without noticing.

I’m not saying all exercise is bad for all people. However, people don’t live in a behavioral vacuum and there are deeper physiological and psychological influences we must be aware of. Not only are we hungrier but we are also more likely to yield to temptation thinking we’ve already paid for our sins in the gym.

Here’s the last reason that fitness trackers are making us fatter. The best workout in the world is the one you actually do. And most people just don’t stick to their exercise goals.

When they fail, people blame themselves instead of the poorly designed weight-loss system. The cycle of yo-yo dieting and subsequent self-loathing makes us fat.

Most fitness apps fail because they miss a critical component of what it takes to change long-term behaviors. Unlike fitness trackers, technologies like Facebook, Twitter, and the iPhone change behavior because they’re fun.

However, by and large, fitness apps are a drag. As data shows, fitness trackers that make people do things they hate doing, fail to change long-term behaviors.

Sure, we can starve ourselves for a while or pay homage to the elliptical machine for a few weeks, but eventually we give up if it’s not fun.

That’s why the only people who sustain using these bossy services are those who were already tracking their activity and nutrition before they started using the app, or the relatively few who somehow learned to enjoy the behavior for their own sake.

To date, the burgeoning fitness app industry has relied too heavily upon game-like incentives to motivate behavior — but games invariably come to an end. When the novelty of extrinsic prizes like points, leaderboards, and step counts wear off, the experience becomes monotonous, and users quit.

Someday, a host of new technologies will finally fulfill the promise of helping us maintain a desirable weight and conceivably live better, longer lives. We’re just not quite there yet. Until then, we should be cautious of products that attempt to change our bodies without first understanding our minds.

Note: An expanded version of this commentary appeared in TechCrunch.