These common and diet mistakes may be sabotaging your weight loss.

I work hard for every pound of weight I lose (and those last few post-baby pounds this year were stuh-born). And I'm sure you do, too, so the notion that something beyond pure willpower is derailing our efforts to shed pounds is downright infuriating. To that end, here are 3 diet "wreckers" to be aware of. Don't let them erase all your dieting hard work.

-Brierely Wright, M.S., R.D.

Diet wrecker #1: Having a morning snack.

People who didn't snack between breakfast and lunch lost nearly 5 percent more weight (an average of 7½ more pounds) over a year than morning snackers in a 2011 Journal of the American Dietetic Association study. Since breakfast and lunch can be only a few hours apart, researchers suspect that most morning snacks are fueled out of habit rather than hunger-and generally amount to mindless eating. So forgo your morning snack, unless you have to go more than four hours until lunch. When you do snack, choose a snack that's satisfying: one that includes protein, fiber-rich carbs and a little fat, such as an apple with peanut or almond butter or a corn tortilla with a slice of low-fat cheese.

Diet wrecker #2: Eating a late dinner.

Mice who eat an early dinner and then fast for 16 hours are slimmer than those who eat the same amount of calories, but snack around the clock, according to a study in Cell Metabolism. Researchers suspect that the longer lapse between meals allows the body to process the food more efficiently. They noticed that even mice fed a high-fat diet gained less weight when they fasted for 16 hours than those who ate more frequently. (Get 2 more reasons to eat dinner early here.)

Diet wrecker #3: Skimping on sleep.

In a small study in the Annals of Internal Medicine, researchers found that when dieters slept 5½ hours a night for two weeks, they burned less fat and more muscle than those who slept 8½ hours. Other research shows that sleeping less than 5 hours per night may cause weight gain to settle around your midsection. Cortisol secretion (the stress hormone linked to belly-fat accumulation) is at its lowest at night, but sleep loss boosts cortisol the day after a night of poor sleep. And even more research-this out of Harvard-shows if you've missed an hour or two of sleep, you're more likely to give in to junk food the next day. The prefrontal cortex-part of the brain responsible for self-control-is compromised by sleep loss.