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 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 Online Journal of Sport Psychology says that loud music may be one of the most effective tools for relieving stress and fighting fatigue.

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.

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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 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.

Don't skip breakfast. Two major studies published in the International Journal of Food Sciences and Nutrition show that breakfast eaters not only feel better mentally and physically compared to people who skip breakfast, but they also tend to have a healthier lifestyle and are better at dealing with depression and emotional stress.

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.

Call a buddy. There's more than a decade's worth of research showing that men who open up and talk about their lives with other people have more energy than men who keep their stress inside.

Get it on. In a 10-year-study of 900 men, U.K. scientists found that men who had sex the most often also had the best physical health and most overall energy.

Catch 40 winks. Been sneaking a nap under your desk? Good. The NIH found that power naps boost brain power, preventing burnout and significantly improving mental performance.

Scramble some eggs. Of all foods, eggs are the best provider of energy-boosting protein, according to the American Heart Association

Swallow some calcium. Calcium deficiencies sap muscle strength and lower physical endurance. The average guy needs at least 1,000 mg of calcium a day.

D up. You need vitamin D to maintain the proper balance of other energy-bolstering vitamins in the body. The best D sources? Fish and D-fortified skim milk.

Get a massage. Studies show that massage helps you conquer three serious energy drainers—anxiety, headaches, and muscle soreness.

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Inflate your ego. Try this classic therapy trick: Grab a piece of paper and jot down seven things you like about yourself. Self-confidence equals increased energy.

Wear brighter colors. Vibrant greens and blues activate neurons in the brain that keep energy at its peak.

Do a puzzle. Pick something challenging. Problem solving stimulates brain cells, spiking your body's energy levels.

Do some cardio. Biking, running, and swimming all help to increase the number of energy-producing mitochondria in your cells.

Do the downward dog. Indian researchers found that men who perform yoga often experience less fatigue during cardiac stress tests than men who don't.

See a funny flick. A study in the journal Psychological Reports found that laughter pushes the energy-sapping compound neuroendocrine out of your brain.

Have a soundtrack. Play background music at your desk. You'll have less anxiety, a prime energy thief.

Get your stuff together. The more organized things are around you, the more mental and physical energy you can devote elsewhere.

Duck debt. Researches at Ohio State found that men who were stressed over their credit card debt had lower energy levels than guys with less debt or none at all.

Stay positive. Australian researchers found that men who had positive attitudes suffered fewer injuries and recovered from injuries faster than their darker—less energetic—counterparts.

Sleep in. Getting even one extra hour of sleep a week can counteract most energy-robbing sleep deficits.

Go out on the town. Sure it's fun, but studies show that a good social life can also help you feel more energetic.

Vary your routine. Switch things around—add intervals to your workout, try new lifts, cross-train. You'll challenge your muscles, furthering their development and giving you more energy.

Relax. Stress is energy's number one enemy. Next time you're swamped, zap the stress by closing your eyes and breathing deeply for 60 seconds.

Schedule a day off. Take a day every month to do something fun—no errands and nothing serious or work-related. The happier you are, the better you feel.

Pump some iron. Anaerobic exercise—like lifting—boosts levels of three compounds your body needs for quick bursts of activity, ranging from sprints to foreplay.

Veg out. Load your plate with veggies like tomatoes, carrots, and spinach. The brighter the vegetables' color, the more energy-revitalizing antioxidants they contain.

Chug a sports drink. The potent mix of water, sugar, and electrolytes may give you the juice you need to make it through that last set.