Decades of research suggest that people who are married lead healthier lives and live longer. But it's the quality of the relationship -- not marriage per se -- that's key to good health, say experts.

So what's the secret of happily (and healthfully) hitched couples? It boils down to the healthy habits they share and rub off on each other. Here are four to cultivate -- as a couple.

1. Eat healthy as a couple

For many folks, marriage and weight gain go hand-in-hand. The reason: Living together means sharing most things, including food supply. If one of you fills the fridge with unhealthy junk food, the other is going to eat it too. And if you watch what you eat, your habits can motivate your husband to do the same. Here are some ideas to spring-clean your diet to encourage healthy eating:

Get rid of the unhealthy stuff

Eliminate junk food from your home.

Get more fresh produce

Stock up on fresh fruits that you can grab for a quick bite.

Make your own meals

Eat at home more often than you eat out and opt for healthier cooking methods to prepare your meals, such as baking or steaming instead of frying.

Buy single-portion snacks

The occasional treats are fine and keep you from feeling deprived -- just buy snacks in single-servings instead of family packs.

2. Stay active as a couple

Recruiting your partner as your exercise buddy gives you quality couple time while you move those muscles. By leading an active lifestyle, you'll stay fit, keep your weight in check and reduce your risk for weight-related health problems.

Do plan physical activities that you'll enjoy together -- whether it's a routine of evening walk, biking through your neighborhood, or a tennis match -- so you're more likely to stick to it.

3. Support as a couple

Spouses can be each other's strongest pillars of support to help us cope with stress in a positive way. The benefits aren't just emotional, but physical, too: A University of Toronto study has found that going home to a supportive spouse brings down blood pressure elevated by a bad day at work.

So spend time with your guy to dish positive encouragements as well as nurture your bond. Make time for couple talk everyday -- no matter how busy you are -- to ensure you stay on top of each other's lives.

4. Resolve conflicts as a couple

ASAP and calmly. Nasty spats are only going to make things worse, and marriages that are filled with chronic fights and discord carry health hazards by creating a high-stress environment.

"All couples disagree -- it's how they disagree that makes the difference," says Howard Markman, professor of psychology at the University of Denver and co-director of the Center for Marital and Family Studies. "You can get angry, but it's important to talk without fighting."

The best thing you can do is to work out a resolution together calmly:

Cool off

Choose a time when you can return to the argument with less emotion -- ideally within 24 hours.

Don't assume

That you know what is he thinking or feeling -- let him have a chance to explain his point of view. And request that he do the same.

Find a middle ground

Recognize you're in a partnership and look for a compromise. This isn't about "winning" or "losing".

Move on

If he has done something that upsets you, you need to learn to forgive and move on. Brooding over past issues is only going to get in the way of intimacy.