Carbohydrates spark a lot of animosity and a lot of love. On one hand, they've been vilified by people who follow certain diets, but nutritionists are quick to tout their virtues.

So are these macronutrients good or evil? The not-so-simple answer is that they're both.

Carbohydrates are found in a wide variety of healthy and unhealthy foods. They're in beans, milk and potatoes as well as cookies, cakes and pies. Some are simple, and some are complex. And new research says they may be one of the reasons humans are so smart.

But let's back up a little bit.

Types of carbohydrates

There are three common types of carbs: sugar, starch and fiber. Here's a basic breakdown of what those are.

Sugar: Sugar is found naturally in some foods, including fruits, vegetables, milk and dairy products. It's also added to some foods during processing like cookies or canned foods that are packed in heavy syrup. In the U.S., the average American consumes 126 grams (about 30 teaspoons!) of sugar every day. The World Health Organization recommends less than half of that, or 50 grams of sugar max per day.

Starch: Starch occurs naturally in some vegetables like potatoes and corn. It's also in dried beans and peas, such as pinto beans, kidney beans and split peas. Many grain products are also high in starch.

Fiber: Fiber is found only in plant foods. It's in vegetables, fruits, nuts, whole grain pastas, cereals and breads, and cooked dry beans and peas.

pretty wrapped muffinPastries, candy and soda have simple carbs. They give you quick energy ... and then a crash. (Photo: Shaiith/Shutterstock)

Simple or complex?

Carbohydrate are classified as either simple or complex. Simple carbohydrates have only one or two sugars. Simple carbs are used quickly and easily by the body for energy because of their simple chemical structure. That may seem like good news if you're dragging and need a burst of energy, but it's usually bad because it can lead to a spike in blood sugar followed by a quick plummet. Soda, white bread, candy and pastries have simple carbs. Although the sugars in fruits and vegetables are simple, the fiber they contain makes them more complex.

Complex carbs are more complicated, as the name implies. With three or more sugars linked together, they have more complex chemical structures. They take longer to digest and have less of an immediate impact on blood sugar, causing it to rise at a slower pace. Because they take longer to break down, complex carbs provide you with even more longer-lasting energy. Complex carbs include whole-grain breads and cereals, and starchy vegetables such as beans and peas.

Typically, complex carbs are considered healthy or "good," while simple carbs are the unhealthy or "bad" choices.

How many carbs do you need?

According to the Dietary Guidelines for Americans, adults should get 45 percent to 65 percent of their daily calories from carbohydrates. The guidelines recommend 25 grams of fiber per day for women and 38 grams per day for men. (The average American gets only about 15 grams of fiber every day.)

Fibers are the carbs with the most-touted health benefits. They contribute to digestive health, keep you regular, and make you feel full longer. Some evidence also suggests that dietary fiber may help reduce the risk of cardiovascular disease, obesity and Type 2 diabetes.

array of colorful high-fiber vegetablesIn general, the darker the veggie, the higher the fiber content. (Photo: yonibunga/Shutterstock)

Be carb smart

Choose your carbs wisely. Even though they both have carbs, a side salad with veggies is a smarter choice than fries, and a bowl of fresh fruit tops a piece of cake (nutritionally, anyway).

Here are some tips from the Mayo Clinic to help make carbs a smart part of a nutritional diet:

  • Emphasize fiber-rich fruits and vegetables. Choose whole fresh, frozen or canned fruits and vegetables without added sugar. Whole fruits and vegetables also have the added benefit of fiber.
  • Choose whole grains. Whole grains are better sources of fiber and other important nutrients than refined grains.
  • Stick to low-fat dairy products. The amount of carbs varies in dairy products, so read the label. Stick to low-fat dairy with no added sugars.
  • Eat more beans and legumes. Legumes are typically low in fat; contain no cholesterol; and are high in fiber.
  • Limit added sugars. Too much added sugar, and sometimes naturally occurring sugar, can lead to health problems such as tooth decay, poor nutrition and weight gain.

Carbs and your brain

Still not convinced carbs have redeeming qualities?

According to a new study published in the Quarterly Review of Biology, carbohydrates could get some of the credit for the evolution of the human brain. Researchers argue that the human brain depends on the consumption of carbs — starch in particular — to thrive. The scientists say carbs were key in the brain's growth and development around 1 million years ago.

Makes you want to have some beans and a whole-grain bagel.

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.