Carbohydrates 101: Why Your Body Needs Carbs
Carbs have gotten a pretty bad reputation.
You've probably heard that you should “cut carbs,” avoid bread and pasta, choose low-carb products, or eat fewer carbohydrates if you want to be healthy.
But carbohydrates aren't something your body needs to avoid.
Carbohydrates are one of the three macronutrients your body needs to function, along with protein and fat. They provide energy, help fuel your brain, and play an especially important role during exercise.
So what exactly is a carbohydrate? What's the difference between simple and complex carbs? And why does your body need them?
Let's break it down.
What Are Carbohydrates? And Why Does Your Body Need Them?
Carbohydrates are a type of macronutrient you eat that your body can break down into glucose and other simple sugars.
Glucose is an important source of energy for your body.
Your brain uses glucose as a major fuel source, and your muscles rely heavily on carbohydrate—especially when you're exercising at higher intensities.
What foods contain carbohydrates?
Grains and starches
Bread
Rice
Pasta
Oats
Cereal
Tortillas
Crackers
Potatoes
Corn
Fruits and vegetables
Apples
Bananas
Berries
Oranges
Sweet potatoes
Peas
Winter squash
Beans and legumes
Black beans
Chickpeas
Lentils
Kidney beans
Pinto beans
Dairy and other foods
Milk
Yogurt
Some plant-based milk and yogurt products
Sweets and desserts
Juice and other sugar-sweetened beverages
In other words, carbohydrates aren't one specific type of food.
They're a nutrient found in many different foods—and those foods can look very different from one another.
Simple vs. Complex Carbohydrates
You've probably heard that there are “good carbs” and “bad carbs.”
I prefer to talk about simple and complex carbohydrates, because these terms describe the structure of the carbohydrate rather than assigning a moral value to the food.
Simple carbohydrates
Simple carbohydrates are made up of one or two sugar molecules and are generally digested and absorbed relatively quickly.
Examples include:
Table sugar
Honey
Syrup
Juice
Candy
Regular soda
Some sports drinks
Fruit
Milk
Fruit, candy and milk all contain simple carbohydrates, but that doesn't make them nutritionally equivalent.
An apple also provides fiber, vitamins, minerals, water, and other beneficial plant compounds. Candy provides carbohydrate in a different form. Milk provides protein, calcium and potassium.
Complex carbohydrates
Complex carbohydrates contain longer chains of sugar molecules, primarily starches and fibers.
Examples include:
Oats
Brown rice
Whole-grain bread
Whole-grain pasta
Potatoes
Sweet potatoes
Corn
Beans
Lentils
Many vegetables
Many minimally processed complex-carbohydrate foods also contain fiber, which can slow digestion and the absorption of glucose into the bloodstream.
And that's one reason these foods often provide more sustained energy and fullness.
One important clarification: not every complex carbohydrate is high in fiber. For example, white bread and white rice contain complex carbohydrates but have relatively little fiber compared with their whole-grain counterparts.
What Happens to Your Blood Sugar When You Eat Carbohydrates?
When you eat carbohydrate, your digestive system breaks some of it down into glucose, which enters your bloodstream.
This causes your blood glucose to rise.
That's normal. In fact, that's exactly what we want to happen when you eat carbohydrates!
The amount and speed of the rise can vary depending on the type of carbohydrate, how much you eat, what else you eat with it, how the food is prepared, and your individual physiology.
Foods containing more fiber and carbohydrates that take longer to digest generally result in a slower, more gradual rise.
Neither response is inherently “good” or “bad.”
Your body is designed to respond to changes in blood glucose.
So Are Simple Carbs Bad?
No.
Simple carbohydrates can be particularly useful when your body needs quickly available energy.
This is one reason they're so useful for athletes.
During longer or higher-intensity exercise, your muscles use carbohydrates for fuel. If you need energy quickly, easily digested carbohydrates can be especially helpful.
Think:
A banana before a run
Applesauce during a long workout
Sports drink during endurance exercise
Gels or chews during a long run
Graham crackers or fig newtons before or during exercise
Juice when you need readily available carbohydrate
You don't necessarily want a huge amount of fiber right before or during a hard workout.
Fiber slows digestion, which is generally a helpful thing—but during exercise, you want carbohydrate to become available quickly.
It's matching the food to what your body needs at that moment.
What About Complex Carbohydrates?
Complex carbohydrates can be a great source of longer-lasting energy, particularly when they're paired with fiber and other macronutrients (like protein and fat).
Think about these complex carbohydrates:
Oatmeal
Whole-grain toast
Brown rice
Beans and rice
Lentils
Potatoes
Whole-grain pasta
Sweet potatoes
The fiber and structure of these foods can slow digestion and glucose absorption, which generally means blood glucose rises more gradually.
That can be helpful when you're eating a meal and want it to keep you satisfied for longer.
But here's an important point:
A slower rise in blood sugar isn't always better.
If you're sitting down to lunch after going six hours without eating, you don't necessarily need to choose the food that digests the most slowly.
You need food - most likely a combination of both simple and complex.
If you're hungry, eating a carbohydrate that provides energy relatively quickly isn't something you need to be afraid of.
Your Body Doesn't Need You to Avoid Blood Sugar Spikes
“Blood sugar spike” has become a scary phrase in wellness culture.
But your blood sugar is supposed to rise when you eat.
Your body has sophisticated systems for regulating blood glucose, including insulin, which helps move glucose from your bloodstream into your cells to be used or stored.
For most people, the goal isn't to keep blood sugar perfectly flat all day.
That's not how human physiology works.
Instead, your blood glucose naturally rises and falls throughout the day in response to eating, activity, hormones, stress, and other factors.
Of course, some people—such as those with diabetes or certain other medical conditions—may need to pay closer attention to blood glucose management. That's where individualized medical and nutrition guidance are important.
But for the average person, seeing your blood sugar rise after eating carbohydrates isn't evidence that you've done something wrong.
Why Does Your Body Like Carbohydrates for Energy?
Your body can make energy from carbohydrates, fat, and protein.
Carbohydrate is a particularly accessible source of energy, especially when your body needs energy quickly.
Your brain also relies heavily on glucose as a fuel source under ordinary conditions.
And your muscles store carbohydrate as glycogen, which can be quickly accessed during physical activity.
This is particularly important for athletes.
If you've ever felt sluggish during a workout because you didn't eat enough carbohydrate beforehand, you've experienced just how useful carbohydrates can be.
This is why sports nutrition recommendations often emphasize carbohydrates before, during, and after exercise.
Carbohydrates aren't getting in the way of performance. They're helping make performance possible.
What Happens When You Go Very Low-Carb?
Your body is remarkably adaptable.
If you dramatically reduce carbohydrate intake, your body can use other fuels and make glucose through other metabolic pathways called gluconeogenesis. This is part of why people can survive without consuming large amounts of carbohydrate.
But “your body can function without much carbohydrate” isn't the same as “your body doesn't need carbohydrates.”
And for many people, maintaining a very low-carbohydrate diet is difficult.
Trying to eliminate or severely restrict carbohydrates can make eating complicated and less enjoyable. It can also make it harder to get enough carbohydrate to support exercise and other physical activity. Restricting carbohydrates can also lead to developing disordered eating habits.
And if your goal is to develop a flexible, sustainable relationship with food, a diet that requires you to constantly avoid an entire macronutrient is not recommended.
The Bottom Line: Carbs Have a Place at the Table
Carbohydrates aren't something your body needs to fear.
They're an important source of energy, they're a major fuel for your brain and muscles, and they're especially important for exercise.
Simple and complex carbohydrates can both have a place in your diet.
Simple carbohydrates can be digested relatively quickly and provide readily available energy—which can be particularly useful around exercise.
Complex carbohydrates, especially those found in fiber-rich foods, generally take longer to digest and can provide more sustained energy and fullness.
The “best” carbohydrate depends on the situation.
Sometimes you want a banana before a run.
Sometimes you want oatmeal for breakfast.
Sometimes you want a bowl of rice and beans.
Sometimes you want a cookie.
And sometimes you're really hungry and the fastest thing available is exactly what you need.
Carbohydrates aren't the enemy. They're food—and your body knows how to use them.
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