By Heidi Grant Halvorson, Ph.D.

Eat less, exercise more. That's the recipe for losing weight, and we all know it by heart. So if we want to get slimmer, and we know the formula, then why can't we do it?

Commitment is important -- in fact, it's essential -- but it's only the beginning. The key to successful dieting is bridging the gap between what you want to do and actually doing it. The desire is there; you just need a plan.

More from Health.com:
I Did It! Weight-Loss Success Stories
Willpower Secrets From the Pros
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The scientifically proven tactics here will help you do just that. I say that with confidence -- not only as a social psychologist who studies motivation, but also as someone who has benefited from these tricks firsthand. Each one -- especially #2 -- helped me lose almost 50 pounds after my son was born three years ago.

Strategy #1: Be Very Specific
When we make goals that are vague, like "I want to lose weight," we set ourselves up to fail.

Motivation happens when your brain detects a difference between where you are and where you want to be. When you are specific about your goal (I want to lose 10 pounds), that difference is clear, and your brain starts throwing resources (attention, memory, effort, willpower) at the problem. A clear target looks something like this: "I want to weigh 135 pounds. I weigh 155 now, so that's a difference of 20 pounds."

Being specific gives you clarity because you've spelled out exactly what success looks like. That means more motivation -- and better odds of success.

Strategy #2: Create An OK-To-Eat Plan
Faced with unexpected temptations -- the dessert menu, the catered work lunch -- we end up eating things that sabotage our weight-loss goals. The best way to guarantee you make the right choices is to create an "if-then" plan:

  • "If the dessert menu arrives, I'll order coffee."
  • "If I am at a business lunch, I'll have a salad."

Studies suggest that coming up with safe-to-eat plans makes you two to three times more likely to reach your diet goals.

Strategy #3: Track Your Success
To stay clear about that gap between where you want to go and where you are now, monitor your progress. Keep getting on that scale; mark the days you exercise on a calendar.

Another thing: When you think about the progress you've made, stay focused on how far you have to go, rather than how far you've come. If you want to drop 20 pounds, and you've lost 5 so far, keep your thoughts on the 15 that remain. When we dwell too much on how much progress we've made, it's easy to feel a premature sense of accomplishment and start to slack off.

Strategy #4: Be A Realistic Optimist
As much as we want to believe otherwise, losing weight isn't easy. It turns out that it's important to accept this.

Believing you will succeed is key, but believing you will succeed easily (what I call "unrealistic optimism") is a recipe for failure. Take it from the women, all obese, who enrolled in a weight-loss program in one study. Those who thought they could lose weight easily lost 24 pounds less than those who knew it would be hard. The successful dieters put in more effort, planned in advance how to deal with problems, and persisted when it became difficult.

So don't try to tamp down your worries -- they can help prepare you for shape-up challenges.

Strategy #5: Strengthen Your Willpower
The capacity for self-control is like a muscle: It varies in strength from person to person and moment to moment. Just as your biceps can feel like jelly after a workout, your willpower "muscle" gets tired when you overtax it.

To strengthen it, pick any activity that requires you to override an impulse (such as sitting up straight when your impulse is to slouch), and add that to your daily routine. And take baby steps. Instead of going junk-free overnight, begin by eliminating, say, those chips you eat by the bag, and substitute them with a fruit or vegetable.

Hang in there, and sticking to your diet will become easier because your capacity for self-control will grow.

Check out our inspiring weight loss stories below:

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  • Linda BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/24/i-lost-weight-linda-herman_n_5534389.html" target="_blank">Read Linda's story here.</a>

  • Linda AFTER

    <a href="http://www.huffingtonpost.com/2014/07/24/i-lost-weight-linda-herman_n_5534389.html" target="_blank">Read Linda's story here.</a>

  • Kelly BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/21/i-lost-weight-kelly-hallock_n_5531333.html" target="_blank">Read Kelly's story here.</a>

  • Kelly AFTER

    <a href="http://www.huffingtonpost.com/2014/07/21/i-lost-weight-kelly-hallock_n_5531333.html" target="_blank">Read Kelly's story here.</a>

  • John BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/17/i-lost-weight-john-henderson_n_5515251.html" target="_blank">Read John's story here.</a>

  • John AFTER

    <a href="http://www.huffingtonpost.com/2014/07/17/i-lost-weight-john-henderson_n_5515251.html" target="_blank">Read John's story here.</a>

  • Christina BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/14/i-lost-weight-christina-liendro_n_5485541.html" target="_blank">Read Christina's story here.</a>

  • Christina AFTER

    <a href="http://www.huffingtonpost.com/2014/07/14/i-lost-weight-christina-liendro_n_5485541.html" target="_blank">Read Christina's story here.</a>

  • DeAnna BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/07/i-lost-weight-deanna-taylor_n_5379433.html" target="_blank">Read DeAnna's story here.</a>

  • DeAnna AFTER

    <a href="http://www.huffingtonpost.com/2014/07/07/i-lost-weight-deanna-taylor_n_5379433.html" target="_blank">Read DeAnna's story here.</a>

  • Paul BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/10/i-lost-weight-paul-jay-birch_n_5474633.html" target="_blank">Read Paul's story here.</a>

  • Paul AFTER

    <a href="http://www.huffingtonpost.com/2014/07/10/i-lost-weight-paul-jay-birch_n_5474633.html" target="_blank">Read Paul's story here.</a>

  • Kourtney BEFORE

    <a href="http://www.huffingtonpost.com/2014/07/03/i-lost-weight-kourtney-luster_n_5406288.html" target="_blank">Read Kourtney's story here.</a>

  • Kourtney AFTER

    <a href="http://www.huffingtonpost.com/2014/07/03/i-lost-weight-kourtney-luster_n_5406288.html" target="_blank">Read Kourtney's story here.</a>

  • Danielle BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/30/i-lost-weight-danielle-gilmore_n_5379289.html" target="_blank">Read Danielle's story here.</a>

  • Danielle AFTER

    <a href="http://www.huffingtonpost.com/2014/06/30/i-lost-weight-danielle-gilmore_n_5379289.html" target="_blank">Read Danielle's story here.</a>

  • Pamela BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/26/i-lost-weight-pamela-arias_n_5405713.html" target="_blank">Read Pamela's story here.</a>

  • Pamela AFTER

    <a href="http://www.huffingtonpost.com/2014/06/26/i-lost-weight-pamela-arias_n_5405713.html" target="_blank">Read Pamela's story here.</a>

  • Sherlonda BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/23/i-lost-weight-sherlonda-tyrus_n_5310512.html" target="_blank">Read Sherlonda's story here.</a>

  • Sherlonda AFTER

    <a href="http://www.huffingtonpost.com/2014/06/23/i-lost-weight-sherlonda-tyrus_n_5310512.html" target="_blank">Read Sherlonda's story here.</a>

  • Justin BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/16/i-lost-weight-justin-willoughby_n_5310166.html" target="_blank">Read Justin's story here.</a>

  • Justin AFTER

    <a href="http://www.huffingtonpost.com/2014/06/16/i-lost-weight-justin-willoughby_n_5310166.html" target="_blank">Read Justin's story here.</a>

  • Kerry BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/19/i-lost-weight-kerry-hoffman_n_5310330.html" target="_blank">Read Kerry's story here.</a>

  • Kerry AFTER

    <a href="http://www.huffingtonpost.com/2014/06/19/i-lost-weight-kerry-hoffman_n_5310330.html" target="_blank">Read Kerry's story here.</a>

  • Lacy BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/12/i-lost-weight-lacy-lane_n_5276296.html" target="_blank">Read Lacy's story here.</a>

  • Lacy AFTER

    <a href="http://www.huffingtonpost.com/2014/06/12/i-lost-weight-lacy-lane_n_5276296.html" target="_blank">Read Lacy's story here.</a>

  • Marqkria BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/09/i-lost-weight-marqkria-mcmiller_n_5226557.html" target="_blank">Read Marqkria's story here.</a>

  • Marqkria AFTER

    <a href="http://www.huffingtonpost.com/2014/06/09/i-lost-weight-marqkria-mcmiller_n_5226557.html" target="_blank">Read Marqkria's story here.</a>

  • Gina BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/02/i-lost-weight-gina-digregorio_n_5153436.html" target="_blank">Read Gina's story here.</a>

  • Gina AFTER

    <a href="http://www.huffingtonpost.com/2014/06/02/i-lost-weight-gina-digregorio_n_5153436.html" target="_blank">Read Gina's story here.</a>

  • Sarah BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/26/i-lost-weight-sarah-swagler_n_5119632.html" target="_blank">Read Sarah's story here.</a>

  • Sarah AFTER

    <a href="http://www.huffingtonpost.com/2014/05/26/i-lost-weight-sarah-swagler_n_5119632.html" target="_blank">Read Sarah's story here.</a>

  • Emil BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/29/i-lost-weight-emil-oprisa_n_5113935.html" target="_blank">Read Emil's story here.</a>

  • Emil AFTER

    <a href="http://www.huffingtonpost.com/2014/05/29/i-lost-weight-emil-oprisa_n_5113935.html" target="_blank">Read Emil's story here.</a>

  • Nikki BEFORE

    <a href="http://www.huffingtonpost.com/2014/06/05/i-lost-weight-nikki-hauck_n_5160077.html" target="_blank">Read Nikki's story here.</a>

  • Nikki AFTER

    <a href="http://www.huffingtonpost.com/2014/06/05/i-lost-weight-nikki-hauck_n_5160077.html" target="_blank">Read Nikki's story here.</a>

  • Lauren BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/22/i-lost-weight-lauren-richmond_n_5111063.html" target="_blank">Read Lauren's story here.</a>

  • Lauren AFTER

    <a href="http://www.huffingtonpost.com/2014/05/22/i-lost-weight-lauren-richmond_n_5111063.html" target="_blank">Read Lauren's story here.</a>

  • Darrell BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/19/i-lost-weight-darrell-mctague_n_5104908.html" target="_blank">Read Darrell's story here.</a>

  • Darrell AFTER

    <a href="http://www.huffingtonpost.com/2014/05/19/i-lost-weight-darrell-mctague_n_5104908.html" target="_blank">Read Darrell's story here.</a>

  • Jessica BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/12/i-lost-weight-jessica-johnson_n_5002531.html" target="_blank">Read Jessica's story here.</a>

  • Jessica AFTER

    <a href="http://www.huffingtonpost.com/2014/05/12/i-lost-weight-jessica-johnson_n_5002531.html" target="_blank">Read Jessica's story here.</a>

  • After BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/15/i-lost-weight-amanda-clay_n_5070828.html" target="_blank">Read Amanda's story here.</a>

  • Amanda AFTER

    <a href="http://www.huffingtonpost.com/2014/05/15/i-lost-weight-amanda-clay_n_5070828.html" target="_blank">Read Amanda's story here.</a>

  • Miesha BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/05/i-lost-weight-miesha-avery_n_4988688.html" target="_blank">Read Miesha's story here.</a>

  • Miesha AFTER

    <a href="http://www.huffingtonpost.com/2014/05/05/i-lost-weight-miesha-avery_n_4988688.html" target="_blank">Read Miesha's story here.</a>

  • Rachel BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/08/i-lost-weight-rachel-reso_n_4913990.html" target="_blank">Read Rachel's story here.</a>

  • Rachel AFTER

    <a href="http://www.huffingtonpost.com/2014/05/08/i-lost-weight-rachel-reso_n_4913990.html" target="_blank">Read Rachel's story here.</a>

  • Shelly BEFORE

    <a href="http://www.huffingtonpost.com/2014/04/28/i-lost-weight-shelly-matthias_n_4980658.html" target="_blank">Read Shelly's story here.</a>

  • Shelly AFTER

    <a href="http://www.huffingtonpost.com/2014/04/28/i-lost-weight-shelly-matthias_n_4980658.html" target="_blank">Read Shelly's story here.</a>

  • Ernie BEFORE

    <a href="http://www.huffingtonpost.com/2014/05/01/i-lost-weight-ernie-lauro_n_4904095.html" target="_blank">Read Ernie's story here.</a>

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