Turns out certain "good-for-you" tips and supposedly healthy habits could be the reason you're not losing weight.

By Mallory Creveling

Here's the lowdown on popular weight loss myths that could be sabotaging your diet.

Weight Loss Myth #1: Committing Only to Cardio

Why it won't work: Running or spinning shouldn't be your reigning workout queens. Strength training is fitness royalty too. The more muscle you have, the more calories you burn at rest, so lift weights at least twice a week. Your body also adapts to workouts when you do them week after week, meaning you'll hit a plateau and the pounds will stop coming off, says Autumn Calabrese, celebrity trainer and creator of 21 Day Fix, a diet and exercise plan. She suggests adding 30-second high-intensity intervals to the treadmill (or bike) by upping the incline, resistance or speed. Do more squats or lunges too, or try using equipment like resistance bands or battle ropes. (For inspiration go to familycircle.com/bestsculptingexercises.)

Weight Loss Myth 2: Cutting Calories

Why it won't work: Eating fewer calories will initially help you slim down, but it probably won't last. Consuming less while moving more, for example, forces the brain into starvation mode. "This creates the perfect storm for long-term failure, because your hunger surges as your metabolism slows," says David Ludwig, MD, PhD, Harvard T.H. Chan School of Public Health professor and author of Always Hungry? Also, not all calories are alike: 100 calories of apple is not the same as 100 calories of chips. Processed carbs spike levels of insulin, which Ludwig calls "miracle grow" for fat cells because it signals them to hoard calories. Then your brain says you need more food. To slim down, focus on food quality instead, specifically healthy fats, natural carbs and proteins.

Weight Loss Myth #3: Waking Up Super Early to Work Out

Why it won't work: If you're also staying up late, you could actually be sabotaging your ability to get sculpted. Skimping on shut-eye leaves you hungrier the next day and more likely to reach for sugary, starchy snacks. It can also destabilize hormones, upping your risk of diabetes and obesity. Make it a priority to get seven to nine hours of sleep each night (resist that Netflix binge!). Stress can increase insulin as well, causing fat cells to pack on pounds and often leading to overeating, says Ludwig. Relieve tension with daily meditation, stretching or 5-minute walks outside.

Weight Loss Myth #4: Cutting Out All Carbs and Fat

Why it won't work: An important PSA: Not all carbs are evil, and fat-free products often have more sugar or additives than regular versions, says Felicia Hackett, RD, nutritionist at Hilton Head Health. On the other hand, full-fat foods (like yogurt) typically leave you more satisfied, so you won't crave another snack. And while saturated fat may harm your health, monounsaturated varieties (found in avocados and nuts) are better for you. As for carbs, they're a crucial part of a healthy, get-slim diet—the fiber fills you up faster and keeps you fuller longer. Just choose 100% whole-grain crackers, pasta and bread, and have more whole fruit and ancient grains such as quinoa.

Weight Loss Myth #5: Working Out Only When You Have a Full Hour

Why it won't work: Don't ditch exercise just because you can't carve out 60 minutes or you're likely to skip out on a regular routine. If you haven't tried HIIT (high-intensity interval training), add it to your repertoire—stat. Doing 30 seconds of all-out effort (like sprints or jump squats), followed by 30 seconds of active rest (such as walking or biceps curls) and repeating four to eight times melts fat faster than an hour of moving at a moderate pace. "Push yourself as hard as you can and you can spend less than half the time working out," says Calabrese. Also keep in mind that a sweaty workout isn't the only way to get in shape. Classes like yoga, Pilates and barre provide toning benefits you won't get from the elliptical and they don't leave you drenched.

Weight Loss Myth #6: Going All-Natural or Gluten-Free

Why it won't work: "All-natural" doesn't necessarily mean healthy—or skinny. The FDA has no set definition for natural, so companies can stamp any of their products this way, says Hackett. Instead, check the ingredients list to make sure you recognize what's there and that high-fructose corn syrup or another preservative isn't in the top three. Unless you're gluten intolerant, gluten-free labels may also be misleading, because these foods are often heavily processed. (Cinnamon buns can be gluten-free, for instance, but not waistline friendly.) If you want to cut down on gluten, eat more veggies, fruits, seeds, legumes and healthy proteins, which will also help you drop a size.

Weight Loss Myth #7: Using the Gym as an Excuse to Overindulge

Why it won't work: You can't lose a significant amount of weight without paying attention to what you eat, says Lawrence Cheskin, MD, director of the Johns Hopkins Weight Management Center. You'd need to walk for about an hour to burn off a small brownie—and that's only one food in a day. While it's okay to have dessert occasionally, don't eat a big portion and plan to work it off later. Aim for 400- to 500-calorie meals and 100- to 150-calorie snacks by filling your plate with fruits, veggies, fish and legumes, and cutting back on empty calories.

Weight Loss Myth #8: Doing a Juice Cleanse

Why it won't work: Juicing has its benefits, but sipping liquid produce alone for days isn't the best approach to weight loss. Even if you shed a few pounds during a cleanse, you're likely to gain them back when you return to eating whole foods. Also, while you get antioxidants with these drinks, they lack fiber to keep you full, protein to support strong muscles and fat to absorb vitamins, Hackett explains. (They do have a lot of sugar, though.) To get fit, eat clean and pump up your intake of whole produce.