What do booze, an aching back, and a bad mood have in common? They all suck away your energy. But you can fight back. We mined hundreds of scientific studies and interviewed dozens of experts to compile 50 of the very best tips to rev your engines--right now!

Nix the nightcap. Alcohol prevents your body from entering REM sleep (the most restful sleep phase). So, even if you're getting plenty of sleep each night, you may not feel fully rested.

Take a 'roid test. If you're tired all the time, you may have a thyroid problem. Other warning signs to look for include weight changes, a hoarse voice, lethargy, and hair loss.

Drink more. Breathing, talking, peeing, even sitting--they all use up the body's water supply. Let your body dry out, and your energy level will dry up as well.

Light up. Turn on your desk lamp or open the blinds and let in some sun. Your body needs vitamin D (from sunlight) in order to help keep energy levels at their peak.

Have your BP checked. Up to 60% of men between 18 and 39 may have high blood pressure, a prime source of chronic fatigue.

Get your snack on. Your body needs fuel to run at its peak. Skip even one meal because you "don't have time to eat" (sound familiar?) and your pep will plummet.

Munch on berries. Doesn't matter what kind, they're all high in energy-boosters called anthocyanins.

Bulk up your diet. Cardiff University researchers found that men with high-fiber diets have less fatigue than men with lower-fiber diets.

Try L-carnitine. The vitamin-like amino acid may help your muscles recuperate more quickly after a hard day at the gym. To feel the jolt, try taking 500 mg a day for at least three weeks.

Get steamed. According to one U.K. study, up to 68% of men feel more energetic after a hot bath or shower.

Eat more fish. Studies show that the omega-3s in foods like tuna and salmon can help fight depression, leaving you happier and more energized. Don't like fish? Try eating more walnuts and flaxseed, or pop a 1,000 mg fish-oil supplement instead.

Turn it up. A report in the Online Journal of Sport Psychology says that loud music may be one the most effective tools for relieving stress and fighting fatigue.

[pagebreak] Join the B-team. The American Journal of Clinical Nutrition reports that many athletes and exercise buffs don't get enough B vitamins. That's bad, since thiamin, B6, B12, and riboflavin are all necessary for the body's production of energy.

Limit lunch to 500 calories. High-calorie meals take longer to digest and end up pulling energy away from other cells in your body.

Take a hike. Instead of slamming some candy when the 4 p.m. blahs strike, take a quick walk around the block. Physical activity oxygenates blood cells, helping to refill your body's fuel tank.

Say "yes" to yogurt. The good bacteria in yogurt helps keep your intestines healthy, allowing them to absorb more nutrients from the foods you eat. And the more nutrients your cells have at their disposal, the greater your energy reserves.

Avoid trans fats. Foods like doughnuts, crackers, and chips raise levels of bad LDL cholesterol in the body. This narrows blood vessels, blocking the flow of oxygenated, energy-rich blood to cells throughout the body.

Opt for whole grains. White bread and pasta spike blood sugar and burn away quickly, sapping energy as they go. Stick with whole-grain foods, which provide longer-lasting fuel.

Have a cup of joe. In small doses, caffeine is a great energy booster, increasing mental alertness and even spiking sexual potency.

Just lose it. Whether you're packing an extra five pounds or 50, the further over your ideal weight you are, the less energy you ultimately have.

Go nuts. Almonds and peanuts are so nutrient dense that a single nut packs enough calories to heat up half a cup of water. Nuts are also high in magnesium and fiber, two proven energy boosters.

Get wet. According to a study in the journal Clinical Neurophysiology, splashing cool water on your face may restore energy even faster than other popular options, like drinking coffee.

Shake it up. The Journal of Applied Physiology reports that men who drink a high- protein shake after working out have more pep than men who refuel on carbs alone.

Clear your sinuses. Men with chronic fatigue are up to nine times more likely to suffer sinus problems than guys who have no problems breathing. An over-the-counter allergy medication may relieve the condition.