Fuel Up: Eating for Optimal Brain Function Use food to improve energy, supercharge mental performance and boost health and wellness.

Being an entrepreneur often means being pushed to physical and mental limits daily. There are long hours; there's a consistent need to perform at full capacity in presentations and meetings; and there's the drive to stay sharp while determining the right strategic direction for the company.

When people get busy or stressed, often the first thing sacrificed is healthy eating -- and that's the opposite of what should happen.

Eating healthy foods is not just necessary for athletes. It can have a powerful, positive impact on your ability to perform at world-class levels on the job. For example, you can eat foods that help you concentrate better, decrease the risk of cancer, give you energy and more.

Luckily, eating for better creativity, focus and problem solving isn't hard. Here are seven simple foods that can help supercharge mental performance.

Related: 7 Essential Habits of a Healthy Entrepreneur

1. Complex carbs

The brain uses the glucose found in carbohydrates as fuel, but we need to eat them in a controlled way to avoid insulin spikes.

Go for complex, slow-digesting carbs packed full of nutrients and fiber to ensure good mental energy all day long. Starchy vegetables (like sweet potatoes), beans, whole fruits (not juice), peas, lentils, brown or wild rice and quinoa are all good sources of complex carbs. Avoid simple carbohydrates (white bread, white rice, white potatoes) and sugary foods and drinks as much as possible.

2. Protein

Foods high in protein provide amino acids that are the precursors for neurotransmitters, which are small bundles of protein that work in the brain to carry signals from one nerve to another.

Eating high-quality proteins during the day builds the right neurotransmitters to power your concentration and mental performance. Healthy proteins include free-range organic eggs, beans, seeds, nuts, cold-water fish and lean organic meats.

3. Dark chocolate

Chocolate containing 70 percent or more cocoa provides all kinds of goodness: fiber, iron, magnesium, copper, manganese, good fats and polyphenols.

Polyphenols improve vascular reactivity, which is the ability of blood vessels to change their diameter so that more oxygen and nutrient-carrying blood can flow through them. Increased blood flow and oxygen to the brain boosts mental performance and alertness. Eat about an ounce of dark chocolate a day for a delicious brain treat.

4. Blueberries

Research has shown that blueberries are packed full of nutrients that help protect the brain from free radical damage and from age-related mental decline. They also improve memory and learning. If you want to keep your brain young, load up on blueberries.

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5. Caffeine

Caffeine improves mental and physical performance by promoting blood flow to the brain and body. More than 200 mg a day (about two cups of coffee, four black teas or eight green teas) may lead to agitation and insomnia, so watch your level of consumption. Try a single espresso right before a big presentation to kick your performance into high gear.

6. Drink water

Nothing will improve or hurt your performance as much as hydration.

People need water to create energy at the molecular level in all of our cells. Low water equals low energy. Try using a water bottle to keep track of how much you drink each day. If feeling tired or foggy, drinking two glasses of water should help.

7. Eat to 80-percent full

OK, so this isn't a food -- but it's a great high-performance trick.

In addition to helping you to live longer, this habit will keep your blood circulating to all parts of your body (not just in your digestive tract) after a meal. So eat smaller meals throughout the day to avoid the energy peaks and valleys that so many face.

Related: Live a Healthier Life by Making Consistency Work for You