Do you have some days when you’re focused and productive for hours, and other days when you wake up with brain fog and feel exhausted by 3PM?

Your ability to focus comes down to mental energy — how much you have, where you get it, and how you use it.

Mental energy may seem abstract, but it’s rooted in biology: your brain’s ability to keep running ties directly to how much ATP your mitochondria produce. ATP is the molecule that your cells use for fuel; if you train your brain cells to make more ATP, and give them the right raw materials to build it, your brain will literally produce more energy, and you’ll feel a profound difference in your productivity and mental clarity.

If you want to learn how to focus, follow this definitive guide to hacking your brain for maximum mental energy, improved focus, and higher productivity.

How to improve focus and mental energy

All your cells run on adenosine triphosphate (ATP), your body’s energy currency. Mitochondria, the power plants of your cells, are constantly making ATP and sending it through your body to fuel everything you do, from walking and talking to exercising and thinking.

That last one, thinking, is a major energy drain. Your brain uses a huge portion of power, especially considering its size; about 20% of your daily ATP production goes to fueling your brain, and your brain cells have a staggering number of mitochondria that create energy day in and day out.

Your brain is an energy hog, and overusing it can drain your energy bank account quickly. If you’ve ever felt unfocused and had poor impulse control at the end of the day, you’ve experienced decision fatigue — every time your brain has to make a decision, it burns a little fuel. If you’re making hundreds of little decisions a day, you’re going to end up burning out much faster.

Fortunately, you can hack your mental energy in a few different ways:

• Make your mitochondria stronger so they produce more energy and improve brain function
• Give your brain the raw materials to make plenty of ATP
• Remove toxins that sap your energy
• Give your brain fewer decisions to make so your energy lasts longer

Head Strong is all about building stronger brain mitochondria to make your brain more powerful than you thought possible. Here are a few of the best ways to make your mitochondria better and increase your mental energy for better brain function and focus.

Keep learning to keep your mental muscles strong

Your brain’s energy requirements are so high that your brain cells live and die by the use-it-or-lose-it principle, literally. Whatever functions you’re not using quickly weaken.

“Brains love to learn,” says Brett Wingeier, Ph,D,, co-founder of Halo Sport, the wearable neurostimulation device made specifically for athletes.

“What’s happening under the hood is your brain cells are firing, and they’re constantly forming stronger and weaker connections that help them work together in exactly the right networks for exactly the right output. And what do we mean by output? That could mean the perfect backhand. That could mean the perfect Ping-Pong overhead spin shot, or it could mean learning a language. It’s all about your brain optimizing itself to get the job done,” Wingeier says. You can listen to the rest of his interview on Bulletproof Radio (iTunes).

To keep your brain strong, find something you’re interested in — a skill, a language, an instrument, an art medium — and spend some time every day practicing and improving.

Neurostimulation to maximize learning

Doctors have used neurostimulation, via devices that send a gentle electrical current through the skin into specific areas of your brain, in a clinical setting for decades.

These devices are becoming more available for use outside a clinical setting. Wingeier’s company, Halo Neuroscience, developed a product that uses electrical stimulation to prime the brain for learning motor activities, like sports and instruments.

“The thing about this technology is you’re still leveraging the brain’s natural mechanisms of learning. Those are so powerful, and so effective, that it doesn’t make sense to disrupt those,” says Wingeier.

You still have to put in the work, though. Think of neurostimulation devices as preheating the oven so it’s ready to cook when you are.

“It’s not The Matrix. We’re not downloading Kung Fu into your brain,” says Wingeier. “It’s using technology to make sure that your brain is dialed in, and ready to use its natural learning mechanisms where and when you want it.”

Design your schedule to match your internal clock

You probably have a part of the day when you’re unusually productive. For some people it’s early in the morning; for others it’s late at night.

Everyone’s body has a different natural rhythm to it. Structure your day so you work during your most energetic times, and rest during the times when you’re less productive. If you usually feel focused between 6AM and 10AM and you want to relax during the afternoon, plan to do all your most challenging and thinking-intensive work first thing in the morning.

Ready to work at 2 AM, but not a morning person? Get your big projects done late at night and sleep in.

Follow your biology instead of fighting against it. You’ll be much more efficient with your energy.

Minimize decision fatigue to become more productive

Create as many routines as possible to remove decisions from your day. Wake up, make your bed, have coffee, brush your teeth, meditate, check email, start work — follow the same routine day after day until it becomes automatic. Setting out clothes and planning your meals, snacks, workouts, etc., in advance will also help. Not having to think about your schedule frees up a lot of mental energy to focus on the important stuff.

And if you have any big or complicated projects to do, or any important choices to make, always tackle them first, when you’re fresh and have plenty of mental resources to dedicate to them. Save smaller tasks like replying to emails for the end of the day, when you don’t have to do any mental heavy lifting.

Upgrade your sleep for more mental energy and focus

Deep sleep is one of the fundamental ways to make your brain stronger. Your brain replenishes neurotransmitters and clears out cellular waste during the deeper stages of sleep, leaving you clear-headed when you wake up. Deep sleep also slows down brain aging.

The single most effective way to improve your sleep is to black out your room. Light degrades melatonin, one of the hormones that makes you sleepy and triggers cellular repair while you sleep. Get light-blocking curtains and use something to cover all the lights on your router, computer, and so on (electrical tape is a good option).

Check out this guide to sleep hacking for more ways to increase deep sleep. Most of the hacks are free and you can start them tonight.

Eat fat and polyphenols to support your brain

A high-fat, low-carb diet keeps your blood sugar stable and low so you have steady energy throughout the day. Some carbs are OK, but cut out as much sugar as you can; it causes energy-sapping brain inflammation and makes your blood sugar spike and then tank, leaving you sleepy and unable to focus.

Make sure you get plenty of polyphenols as well. Polyphenols are powerful anti-inflammatory compounds that you find in coffee, tea, chocolate, and colorful vegetables and fruits. Polyphenols improve memory and decrease brain inflammation. They also protect your brain from stress.

Check out the complete one-page Bulletproof Diet Roadmap for a complete guide to brain-building foods you should eat and energy-sapping foods you should avoid for improved focus and brain power.

Exercise to grow new mitochondria

Working out is amazing for your brain’s energy production. Pushing yourself physically makes you mentally fit, too: it creates brand new neural mitochondria and makes your existing mitochondria more efficient at producing energy.

Manage stress and practice gratitude

Stress burns up a huge amount of energy. It also physically changes parts of your brain that regulate attention and focus. You lose memory function and your planning skills suffer when you’re stressed.

Stress is universal, and it can sap your energy you if you don’t consciously manage it. Two great options for managing stress are:

• Meditation. Meditating decreases psychological stress and eases anxiety. It also actively improves cognitive function, particularly when it comes to focus.
• Gratitude. Take a couple minutes every day to acknowledge a couple things for which you’re grateful. Gratitude increases coherence between different brain networks, which helps you be more decisive, and increases your mental resilience to stress.

Take nootropics to unlock a more powerful brain

Nootropics (also called smart drugs) are compounds that improve cognitive function. You can use nootropics to enhance everything from memory to sustained attention to faster mental turnover.

Brain Octane Oil is a great introductory nootropic; it rapidly converts to ketones that your brain can use for fuel.

Unfair Advantage is another good option. It supports your brain mitochondria and promotes the growth of new ones for improved mental energy.

For a more complete list of nootropics, including benefits, side effects, sources, and dosages, check out the Bulletproof guide to nootropics.

And for a comprehensive look at brain hacks that enhance cognitive function and help you build a stronger brain, pick up a copy of Head Strong.