It’s not just an old man’s problem, either. Men in their 30s and 40s also fall prey to low testosterone counts. It’s a disorder called hypogonadism, and it can be caused by an undescended testicle, a testicular injury, a pituitary gland disorder or even prescription drugs. It usually goes undiagnosed until a man hits his doctor with a telltale complaint: “I can’t get an erection.”

“If you have reduced levels of sexual desire, have your testosterone level checked immediately,” says Dr. Allen Seftel, a urologist at Case Western Reserve University Hospitals of Cleveland. You can replenish your testosterone stores with injections, gels, pills or patches, but these medical treatments are no panacea: Side effects include acne, high cholesterol, shrunken testicles and liver damage. Further, don’t take supplements like DHEA or androstenedione to boost testosterone; they might increase your risks of prostate cancer and heart disease.

“For men with borderline testosterone scores, I advise them to try to raise their levels through exercise and weight loss before going on testosterone therapy,” says Dr. Goldberg. And it might pay to start young. “Since your testosterone declines at a steady rate, it’s conceivable that raising your hormone levels naturally in your 20s and 30s could help you maintain higher levels later on,” he says. Either way, the reward can be a stronger physique and better bedroom sessions than you’d otherwise deserve. Below are 13 tips designed to get your juice up—safely.

Get Rid of the Flopping Belly

Or you’ll grow a pair of fetching breasts to complement it. Carrying excess body fat elevates your estrogen levels, and that may cause your testosterone levels to sink, says Joseph Zmuda, an epidemiologist at the University of Pittsburgh. Louie Anderson is proof enough of this. Two or three extra pounds won’t cause this hormonal shift; it really occurs once you’re 30 percent over your ideal body weight. “Unfortunately, that’s pretty common now,” says Dr. Dobs.

But Lose Only One Pound a Week

When you want to trim down quickly, you probably starve yourself while exercising like a madman. One of the many reasons this stops working in your 30s, when your natural testosterone levels start dropping, is pretty simple: Cutting your calorie intake by more than 15 percent makes your brain think you’re starving, so it shuts down testosterone production to wait out the famine. “There’s no need to reproduce if you’re starving,” explains Thomas Incledon of Human Performance Specialists in Plantation, Fla. Ironically, this dive in circulating testosterone stops you from burning body fat efficiently, so you’re actually thwarting your hard efforts to melt that tire off your gut.

Skip the Atkins Fad

Research suggests that eating a high-protein, low-carbohydrate diet can cramp your testosterone levels. High amounts of dietary protein in your blood can eventually lower the amount of testosterone produced in your testes, says Incledon, who observed this relationship in a Penn State study of 12 healthy, athletic men.

Your protein intake should be about 16 percent of your daily calories, Incledon says. So, if you’re the average 170-pound man who eats 2,900 calories a day, you should eat about 140 grams of protein daily, which is about the amount in two chicken breasts and a 6-ounce can of tuna.

Have Morning Sex

German scientists found that simply having an erection causes your circulating testosterone to rise significantly—and having one in the morning can goose your natural post-dawn testosterone surge. It’s a sure bet you’ll burn a little fat, too.

Stick With Tough Exercises

To beef up your testosterone levels, the bulk of your workout should involve “compound” weight-lifting exercises that train several large muscle groups, and not just one or two smaller muscles. For example, studies have shown that doing squats, bench presses or back rows increases testosterone more than doing biceps curls or triceps pushdowns, even though the effort may seem the same. This is why doing squats could help you build bigger biceps.

Make Nuts Your Midnight Snack

Nuts are good for your nuts. Research has found that men who ate diets rich in monounsaturated fat—the kind found in peanuts—had the highest testosterone levels. “It’s not known why this occurs, but some scientists believe that monounsaturated fats have a direct effect on the testes,” says Incledon. Nuts, olive oil, canola oil and peanut butter are good sources of monounsaturated fat.

Squeeze Out Five Repetitions per Set

Throwing around 5-pound dumbbells won’t help you effect a rise in testosterone. Start off by using a heavy weight that you can lift only five times. That weight is about 85 percent of your one-repetition maximum. A Finnish study found that this workload produced the greatest boosts in testosterone.

Do Three Sets of Each Weight-Lifting Movement

Researchers at Penn State determined that this fosters greater increases in testosterone than just one or two sets. Rest a full minute between sets, so you can regain enough strength to continue lifting at least 70 percent of your one-rep maximum during the second and third sets.