With two-thirds of American adults considered overweight, a lot of people are trying to shed pounds. It can be a challenging journey, and many folks find that they get tripped up by a major obstacle: themselves. Here are some common ways dieters sabotage their own efforts.

All or nothing

We tell ourselves we’re either dieting or not, and we veer from starving to overindulging. "The more you live in the extremes of all or none, good or bad, the more likely that’s going to get you into difficulty," says Gary Foster, chief scientific officer for Weight Watchers International. "The key is that this is a lifestyle. When it’s an on-or-off diet or a boot camp mentality, that’s a short-term behavior. It’s destined not to work out very well."

The lost weekend

Sometimes when we overeat on a Friday night, we figure we’ve blown the entire weekend. This inevitably leads to a very remorseful and grumpy Monday morning. Is there a better way? "I have my patients picture meals as individual bubbles throughout the day. Pop them as you go along. One isn’t dependent on the other, and you can keep your overall plan in place," says Kelly Allison, associate professor of psychology at the University of Pennsylvania’s Center for Weight and Eating Disorders.

No chocolate chip cookies ever

"When it’s a forbidden food, you’re more likely to overeat once you do have it," says Foster. A different approach is to figure out a way to incorporate that food into your life in moderation. Keeping a stash in your kitchen may not work. Even if, say, the cookies are double-wrapped in the freezer, they’re going to call out to you when you’re most vulnerable. Instead, when a craving hits, try another tactic, such as visiting the best bakery in town and savoring one or two cookies with a good cup of coffee. "If you give yourself permission, but in reasonable portions and frequency, that’s where you strike a nice balance," says Foster.

Crash dieting for a big event

There’s nothing like a wedding or a school reunion to inspire a diet. Often, however, as soon as the event is over, we go back to an unhealthful eating pattern. "These short-term changes produce short-term weight loss. Typically they involve more extreme forms of food restriction that cannot be maintained, a sprint instead of a marathon, which is what a healthier lifestyle really is." says Allison.

Letting the scale mess with your mind

You’re doing all the right things, but when you stand on the scale, the number makes you feel like a failure. The solution here is simple: Weigh in only once a week. Your weight can fluctuate for a variety of reasons, and checking it every day may not give you an accurate assessment. Are your clothes getting looser? Do you have more energy? These are positive indicators that you are succeeding. "Let the scale be a guide, but it’s not a judge. It’s not an arbiter of your success, especially in the short term," says Foster.

Getting too little sleep

Being sleep-deprived appears to change how our brains respond to food. "Judgment and decision-making brain regions become blunted by sleep deprivation when making food choice decisions," says Matthew Walker, a psychology professor and sleep expert at UC Berkeley. He explains that with too little sleep the brain structures that control our impulses and desires get out of whack.

Believing you don’t like veggies

"Leave behind the old-fashioned notion of plain, steamed, undressed vegetables as the best way to go. That’s boring and borders on punitive," says cookbook author Mollie Katzen ("The Heart of the Plate: Vegetarian Recipes for a New Generation"). She advises being creative: Brush veggies with olive oil and singe them on the grill or roast in the oven. Flavor them with sauces made from pulverized nuts, herbs or roasted red peppers. Add caramelized onions, fresh lime juice, garlic or chile peppers for more flavor. "Food needs to be delicious and desirable. If the emphasis is simply on ‘healthy,’ people who are skeptical won’t be pulled in," says Katzen.

Not drinking enough water

Brenda Davy, a nutrition professor at Virginia Tech University, conducted a study with 48 middle aged and older adults, dividing them into two groups on low-calorie diets. One group was instructed to drink two cups of water before meals. "We were interested in whether or not that would help them eat less and lose more weight over 12 weeks. And in fact, it did," says Davy. That group lost about 5 more pounds than the other group.

Joining the clean plate club

Most of us were taught to clean our plates when we were kids, and the pattern has continued into adulthood. A recent Cornell University study found that adults eat nearly all the food they serve themselves. At restaurants, ask for a to-go box right when the meal is brought to the table and save half the food for another time. At a buffet, sample mini portions of a variety of dishes. At home, consider using a smaller plate. You can fill it up and eat everything — without guilt.

Letting others steer you off-course

Sometimes, the people you live with and love are not thrilled when you start losing weight. They might be afraid that your relationship will change. If someone is tempting you with trigger foods, you need to speak up, says Allison. "Is there anybody who is bringing home doughnuts and waving them in front of your face? How can you address that? If they want those foods, they can have them outside of the house."

Nighttime noshing

"There is some evidence to suggest that we don’t want to be eating a lot late at night, but that is very different from saying you cannot have a snack," says Allison. However, she cautions that eating after dark may lead to a slippery slope: "Emotionally and physically, we’re tired at night and we’re looking for comforting things. We’re more likely to choose the higher-calorie foods than we are during the day. Thinking ahead and portioning them out becomes really important."