What's the secret to great sex? There are many, actually, but here's one you probably haven't heard much about: being in good physical shape.

Sex isn't strenuous, but it is exercise. Just as physical conditioning makes working out more enjoyable, getting in shape enhances lovemaking — especially for couples over 50. Try following these seven simple health tips to stay as fit as possible.

See also: Want to improve your health? Have sex!

Simple lifestyle changes can improve your sexual stamina and performance. — Photo by Ken Wramton/Getty Images

1. Exercise daily

In a study of 1,709 men over 40, researchers found that the more the men exercised, the fewer sexual problems they reported. Why would that be? Because exercise increases blood flow to the genitals. It boosts testosterone, which fuels libido in both genders. It also elevates mood, reduces insomnia, helps control weight, promotes deep relaxation, minimizes menopausal discomforts and contributes to self-esteem. All six of those factors enhance libido and sexual satisfaction.

How you exercise doesn't matter. Do anything you enjoy: walking, swimming, yoga, dancing, golf, gardening — whatever. Just make sure you do it at least 30 minutes a day.

Regularity will benefit you more than intensity. It's better for health and sex to take a 45-minute walk every day, for example, than it is to hike five miles twice a month.

2. Eat more fruits and vegetables

Fruits and vegetables are rich in antioxidant nutrients, which promote cardiovascular and neurological health. By contrast, meat, cheese, fast food, junk food and whole-milk dairy products are not just low in antioxidants but high in cholesterol and saturated fat; those last two narrow the arteries, restricting essential blood flow to the genitals.

In a 2006 study, Italian researchers found that a Mediterranean diet — high in fruits and vegetables, low in meat — improves sexual function in men. Within two years after embracing a Mediterranean diet, one-third of the men in the study who had erectile dysfunction reported restored erections. A year later, the same research team reported that a Mediterranean diet improves women's sexual function as well. (Olives, anyone?)

So how do you max out the fruit and veggies? Include fruit with breakfast. Eat at least one salad a day. Snack on any fruit. And one night a week, cook a big pot of vegetable soup, then make it your dinner — and several lunches later in the week.

3. Maintain recommended weight

Many overweight adults enjoy sex, but the research is clear: Weight loss improves lovemaking.

Duke researchers surveyed the sexual impact of weight loss among 70 obese adults. Moderate loss — 10 to 30 pounds — boosted their libidos, sexual function and erotic satisfaction. Brown researchers surveyed 32 overweight women starting a weight-loss program. After losing an average of 56 pounds, most reported more sex and greater erotic fulfillment.

It's tough to lose weight, yes — but guess what helps? Daily exercise and a diet full of fruits and veggies. (Are you starting to see a pattern here?) Exercise burns calories, and plant foods are filling but low in fat. A reasonable goal is two pounds a month. That may sound unambitious, but by year's end there will be 24 pounds less of you in bed.

Next: Tip 4 — Keep the sex killers at bay! »