The mistake:
Thinking "vegan" = "healthy"

How it hurts: "Often there is a myth that following a vegan diet will naturally cause weight loss," says Sheth. Not only can eating vegan-approved foods like nuts and seeds add extra calories and fat, eating junk food, just like with any other diet, will lead to weight gain. Yes, even those seemingly healthy vegan donuts and cookies. The fix: Next time you see that vegan cookie, skip it. Or, at the very least, eat them occasionally, and remember to think of them as a treat, not a health food. Sheth says to emphasize whole foods like veggies, fruits, and whole grains and lean proteins like beans and lentils.

The mistakes:
Not paying attention to food quality
Cutting calories too low

How they hurt: If you cut your calories too low, simply put, you're depriving your body of the fuel it needs to function. Sure, you may lose weight at first, but it will eventually slow down your metabolism and you'll lose calorie-burning muscle mass, says Sass. Plus this can lead to other unwanted side effects, like a weak immune system and trouble sleeping -- not to mention dry skin and hair. She also notes that research has shown we burn 50 percent more calories metabolizing whole foods versus processed foods. "I've had clients break a plateau or start losing weight by eating the exact same number of daily calories, but switching from processed foods to whole foods, so quality is really key," she says.

The fix: Swap out those 100-calorie cookie packs for 100 calories of whole food, like nuts, lean protein or even starchy veggies -- your waistline (and your taste buds) will thank you. Also, know how many calories you should really be eating. A 1,200-calorie diet is thrown around like it's some magical weight loss number, but in reality you need a minimum of 10 calories per every pound of your weight goal if you're inactive, says Sass. That number goes up to 15 if you're moderately active. To put that in perspective, Sass says if your goal weight is 125 pounds and you are moderately active, you should be munching on 1,625 calories a day.

The mistake:
Thinking "eyeballing" is a valid form of measurement

How it hurts: It's easy to over-indulge in the staples of this diet, like olive oil and (especially) wine. And if you're not accurately measuring your portion sizes, the calories add up quickly -- especially for olive oil, which can add hundreds of excess calories to your meals, says Sheth. Plus, Sass says that since wine is an appetite stimulant, overdoing it on the Pinot can make you more prone to overeating (especially if you're trying to eyeball other food measurements). It can also make you more likely to indulge in foods you would steer clear of if you were a little less tipsy (like, say, Taco Bell or your hidden stash of treats).

The fix: The recommended daily amount of wine is no more that one five-ounce glass for women. And before you even ask, no, those glasses you didn't drink Monday through Thursday don't roll over to the weekend, says Sass. As for the olive oil -- always use a measuring spoon instead of just drizzling it over your salad or pouring it directly into your pain, recommends Sheth.