You're two weeks into your diet and you're inhaling a large pizza for one. You've missed your last three workouts. Hey, a person's only got so much willpower.

You're right. Research shows that willpower is partly genetic; there are physical differences in the brains of strong-willed people and their weak-willed counterparts. Lucky for the latter, your willpower is like every muscle you inherited from mom and dad - able to grow stronger. But you need the right workout and fuel to make it happen.

Here, 10 science-approved ways to strengthen your willpower - and your health.

PRACTICE, PRACTICE, PRACTICE

Mom was right: Practice does make perfect. A recent study from The Miriam Hospital's Weight Control and Diabetes Research Center found that when you "exercise" your willpower by practicing self-control - munching on veggies even when the candy aisle is calling your name or showing up to a gym class you'd rather skip - you actually strengthen your willpower in all areas of life. And no, that's not just habit, says Tricia M. Leahey, Ph.D.

Consider this: While study participants' "exercise" was healthy living, their willpower test was definitely not just a matter of sticking with their workout plans. They had to squeeze a handgrip as long as they could despite cramping, fatigue, and flat-out pain. Practice willpower in any area of your life can soon you'll see the benefit on your waistline.

WORK UP TO IT?

When you give into (cheesy, carb-filled) temptations, it's because your willpower is running on empty. The easy way to fill it up? Never let it hit E in the first place. If you overwork your willpower, you can't control yourself later on - even if the tasks at hand seem completely unrelated.

In one study, dieters were given ice cream after watching a movie. The participants who were instructed to stifle their emotions (happy, sad or otherwise) during the film ate more ice cream than those who didn't. Holding back emotions during the movie they had sucked their willpower dry. The solution? Start small, according to lead study researcher Kathleen Vohs, Ph.D, professor of marketing at the University of Minnesota. Studies show that people who make small changes - like improving their posture or brushing their teeth with their opposite hand - can up their self-control in as little as two weeks.

WATCH RERUNS

Finally, a "healthy" excuse for TV time! Studies from the University at Buffalo's Research Institute on Addiction has found that when people watch repeat episodes of their favorite shows, they instantly have more self-control than those who don't. Researchers believe that watching reruns taps the surrogate relationship you've formed with their characters, and since you already know what's going to happen, you can just sit back an enjoy it, which helps to restore your energy. If the pantry tempts you come midnight, stick to reruns before bed.

Remember: This only works with reruns. It's not an excuse to finally watch the first season of "Downton Abbey." It'll just get you worked up and sap your energy.

THINK LONG-TERM

Self-control lags when you're caught up "in the moment" and are distracted you're your long-term goals, Vohs says. To keep a comfy couch from distracting you from your goal to hit the gym four days a week, make sure you have plenty of reminders wherever you are. While the longstanding tradition involves taping unflattering pictures on the fridge, writing down your goals and keeping them with you also works. Or treat yourself to a piece of jewelry that you wear all the time to remind you of your goals and commitment to them.

"Think about where you've been, where you are, and where you're going," says Sylwia Wiesenberg, Founder of Tonique Fitness in New York. "Yes, life is short. But is this really worth it?"

Reminding yourself to pause and think things through can help break even the most unhealthy automatic habits.

TRY YOUR MEMORY

What do willpower and memory have in common? Gray matter. In one Virginia Tech study, researchers asked patients at a substance abuse facility to memorize series of numbers, words and letters in games that targeted their working memory. After a month of memory games, participants had a 50 percent decrease in their rate of delay discounting (that's science talk for swapping long-term rewards for instant ones).

By building up underlying cognitive circuits (mostly in the prefrontal cortex), memory exercises may help people resists instant rewards and stay locked on their long-term goals, according to researchers. Check out lumosity.com for online memory games, or dig out the old Memory card game to play with your kids.

EAT A SNACK

Your stomach won't be the only thing that's fueled. Research shows that restoring blood glucose levels helps to replenish self-control. Glucose fuels many brain functions, and when its levels drop, so does your ability to focus and control impulses. Luckily, eating a small something every few hours can level out blood sugar so your brain has energy to stay in self-control mode.

While carbs can raise your glucose levels quickly, your body burns through them quickly. Pair them with some protein so that your willpower doesn't ride a blood sugar rollercoaster, suggests Kelly McGonigal, a Stanford University psychologist and author of "The Willpower Instinct: How Self-Control Works, Why It Matters, and What You Can Do to Get More of It."

TAKE A NAP

If you are going to test your willpower, do it when you're well rested. Sleep improves brain function and self-control. In one study of hard drug addicts, McGonigal found that those who slept for seven hours a night had higher relapse rates than those who scored an extra hour of shut eye a night.

If you can't always squeeze in a solid night's sleep, consider a mid-day power nap, Wiesenberg suggests. Research shows it can reduce stress, improve mood, restore focus and quell the willpower drain that happens as the day wears on.

LAUGH A LOT

It really is the best medicine. A good dose of the giggles - and even indulging in a funny video - can help people perform better on self-control tasks, according to McGonigal. While experiencing and expressing positive emotions are linked directly increased willpower, laughter also fights stress, increases blood flow, bolsters the immune system, and aids in sleep - all of which can help your brain flex its willpower muscle.

So what if you have to fake it? Forcing a smile can actually decrease stress, according to a recent study in Psychological Science. And thinking back on funny times may be extra helpful. "Research points to the power of conjuring up reminders of what you truly value in life. Is it the love of your partner or the passion in your job? Or a relationship with a higher power?," says Vohs. "Being reminded of those things improves self-control."

CHEER ON OTHERS

Forget yawns, willpower is what's really contagious. Just by observing some else pursue a goal, you'll be else pursue a goal, McGonigal says. Whether or not you are into the group fitness thing, you can still take an interest in your friends and family's goals and encourage them in achieving them.

The trick even works with surrogate friends and family, according to McGonigal. Watching the stars of your favorite reality show work hard to overcome obstacles - whether it's getting healthy on "The Biggest Loser," cooking the perfect dish on "Chopped," or designing a runway showstopper on "Project Runway" - can increase your personal willpower. Warning: A lack of self-control is also contagious. So steer clear of people (and TV stars) who just don't know how to say no, she says.

SIP SOME CAFFEINE

The country's Joe-drinking workaholics are right: Coffee really can help you power through.

Studies show that small doses (yes, a Trenta is too much!) of caffeine can help balance the autonomic nervous system, making your noggin more alert and calmer at same time. What's more, the shot of caffeinated energy can temporarily quell the willpower drop that's associated with fatigue. But limit your caffeine to before lunch. Caffeine can rev your system for up to 12 hours after consumption, which can easily lead to tossing, turning, and giving into temptation.

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