What is the Primary Function of Carbohydrates

“What is the Primary Function of Carbohydrates” was written by Jenny Ingolia and reviewed/edited by Kasey Hageman MS, RD, LD. Jenny is a graduate dietetic student at Clemson Univeristy.

What is the primary function of carbohydrates?

Starting in the 1960s with The Atkins Diet and the recent popularity of the keto diet, carbohydrates have gotten a bad rep. Unfortunately, these claims are lacking in scientific evidence and can cause more harm than good. We live in a world where diet culture has led us to believe that carbs cause weight gain and chronic health diseases.

However, this is not true. In reality, any macronutrient can cause weight gain if you’re eating excessive calories.

The key to success with carbohydrates is balance. A simple way to achieve this is by using the balanced plate method. In other words, this method focuses on including more vegetables, specifically non-starchy vegetables and is based on a 9-inch plate.

If you are a visual person, think of a plate with ½ of it vegetables (non-starchy), ¼ of it a carbohydrate source (whole grains or starchy vegetables), and ¼ protein (fish, chicken, eggs, beef, etc.).  

Carbs tend to be widely available and delicious so avoiding them all together isn’t necessary because they can be a part of a balanced, unrestricted diet! 

Carbs are our body’s preferred source of energy (keyword: preferred). Just FYI, fat can provide our bodies with energy too but it isn’t as efficient as carbohydrates. However carbs provide 4 calories (measure of energy) per gram.

Above all, the primary function of carbohydrates is to give our body energy for the multitude of processes it undergoes. Carbs are also crucial for our brain and red blood cells as they cannot use energy from another source. 

What are the types of carbohydrates?

So what are carbs? In the simplest forms, they are sugars. Glucose, fructose, lactose, maltose, etc. are all types of sugars aka sources of carbs. Carbs can be broken down into categories including simple carbohydrates and complex carbohydrates. Let’s discuss.

Type of SugarWhat is it?Where can it be found?
GlucoseSimple sugar; main sugar in your bloodPasta, bread, potatoes, rice, etc.
SucroseTable sugarBaked goods, cereals, maple syrup, some fruit juices and dried fruits, store-bought pasta sauce (with sugar added), flavored dairy products, etc
FructoseSimple sugarFruit, honey, fruit juices, agave, some baked goods, candy, sodas, etc
LactoseGalactose + glucoseDairy products
MaltoseGlucose + glucoseWheat, barley, honey, alcohol including liquor and beer, etc.
GalactoseSimple sugarSome fruit juices, milk, cheddar cheese, various fruits like grapes and pineapple, beans, apple sauce, tomato paste, etc.

Difference Between Simple and Complex Carbohydrates

Simple Carbohydrates

Simple carbs are those that are quickly digested including glucose, fructose, and lactose. They are digested and absorbed quickly providing your body with a fast source of energy.

As a result, simple carbohydrates also create a spike in blood sugar since they are digested so quickly. For example, simple carbohydrates tend to be found in foods like:

  • White bread
  • White pasta
  • Baked goods
  • Dairy products
  • Fruit

Simple carbs can be a part of a healthy lifestyle and do supply some benefits like iron and thiamin in white rice and or calcium and vitamin D in dairy products. In addition, simple carbs are also a great pre-workout snack. Since they provide the body with quick energy, consuming some before a workout or athletic event, may help with your performance (more on that later).

Complex Carbohydrates

Complex carbohydrates include starch and fiber. For example, you can find these in vegetables, whole grain products, and beans. According to the USDA half of your carbs should be complex. This is due to the overall higher content of nutrients like fiber and vitamins. 

Fiber is essential for our digestive health and can help in lowering the risk of chronic disease. Complex carbohydrates take a little longer to digest since they do contain fiber which in turn helps keep you feeling fuller longer.

As a result, this slow digestion helps prevent a spike in blood sugar which can reduce sluggishness and fatigue later due to a “sugar crash.”

This primary function of carbohydrates, level blood sugar, is one of the most important functions!

Carbohydrate Requirements

The carbohydrate requirement for an individual will vary. That being said, a general recommendation for carbohydrate needs is 45-65% of your total daily calories. If you’re not sure what your needs should be, working with a registered dietitian can be beneficial. 

Research has shown that not getting enough carbohydrates in your diet may cause harmful outcomes.3 

Side effects of low carb diets include:

  • Low energy
  • Fatigue
  • Cramps
  • Headaches
  • Flu-like symptoms (especially for those on the keto diet)

Bottom line: carbs are an important part of a balanced diet and limiting them can cause more harm than good.

Carbs & Weight Loss

There is a common tale that restricting carbs is the answer to losing weight. While there is some truth in that statement, it isn’t the carbs themselves that cause weight loss or gain. 

Being in a calorie deficit is how you lose weight. While reducing your carbohydrate intake could be beneficial for your weight loss goals, it should not be the only macronutrient you are reducing. 

On the contrary, carbs can actually be a beneficial part of weight loss. One of the primary functions of carbohydrates in complex carbs is to Carbohydrates, especially complex, can regulate your blood sugar levels which in turn can help prevent fatigue, afternoon crashes, shakiness, etc. 

Further, incorporating a balance of simple and complex carbs will provide energy not only for your overall health but also for your workouts, day-to-day activities, etc. 

Wouldn’t you be more motivated to lose weight if you had the proper energy and actually felt good? 

You can use the primary function of carbohydrates to reach your weight loss goals!

List of Good Carbs for Weight Loss

VegetablesRich in fiber which keeps you fuller longer and helps maintain a healthy digestive system; Plethora of vitamins and minerals Spinach, broccoli, squash, zucchini, carrots, green beans, asparagus, collard greens, celery, beets, etc.
Whole-grain breadsCan be rich in fiber but also protein which will also keep you full and also help with muscle recoveryEzekial bread, Dave’s Killer bread, Arnold’s 100% Whole Wheat breadIf buying store brand breads, look for low added sugar and high fiber (3-5g per serving), and 100% whole wheat as the first ingredient
FruitFiber + plethora of vitamins, minerals, antioxidantsBananas, apple, pineapple, mango, berries, kiwi, pears, grapes, peaches, etc.
DairyGreat addition for creaminess to recipes; good source of calcium, vitamin D, proteinMilk, cheese, yogurt
Whole grain productsFiber, B-vitaminsBrown rice, quinoa, whole-wheat pasta, oatmeal, popcorn

The options are endless but the consensus is the same: carbs are not the bad guy and can be a part of your weight loss journey!

Carbs & exercise

Above all, the primary function of carbs is to provide energy for your body. That is to say, in order to have a successful workout, your body needs adequate energy in order to perform those exercises. 

Have you ever been exercising and felt overall fatigue, shortness of breath, or severe cramping, during your workout? If so, maybe you noticed that you aren’t completing as many reps as you have before? 

One reason this could be happening is your body does not have enough carbs to convert to energy for your workout. 

When you eat carbs, the sugar in them gets converted to glucose which then provides fuel to your muscles. When working out, this is the energy source your body uses. This is what allows your body to lift weights, run, etc. 

When it isn’t needed, this glucose is converted to glycogen and is stored in your muscles and liver for later use. After working out, it is important to consume a carb source in order to replenish these stores. 

Strategically consuming carbohydrates before your workout could actually improve your performance.2 However this could vary from person to person but the general rule of thumb is to eat a meal consisting mainly of carbs and protein 2-3 hours before your workout and a small carb snack 30 minutes before to provide quick energy for your workout.

Examples of a pre-workout meal

  • 2-3 hours before: Turkey sandwich (Boars Head no salt added, Butterball natural inspirations or low sodium deli meat directly from the deli counter) on whole wheat bread (like the brands I mentioned above) or tortilla with lettuce and tomato, crackers (Triscuit original, Mary’s Superseed crackers or CrunchMaster Multigrain Gluten-Free crackers) and a banana with peanut butter (natural varieties like Crazy Richards or Smuckers Natural- look for just peanuts and salt on the label)
  • 30min before: a small granola bar like a Quaker chewy bar or a small pack of fruit snacks like Stretch Island varieties 
  • For another great pre-workout snack, check out my recipe for Healthy Pumpkin Muffins.

We all know that exercise is good for us and can help us to lose weight. However, if your workouts are fueled properly, it could lead to even greater benefits like more pounds lost.


So in conclusion, eating adequate carbs for your overall health is important and yes, even for weight loss.

The primary function of carbohydrates is to provide your body with the energy it needs to carry out all the reactions it facilitates, proper blood sugar levels, healthy cells and brain tissue, and physical activity. Therefore, carb restriction can lead to harmful effects including chronic fatigue, headaches, and cramps.

In order to improve overall health, including a variety of carbs in your diet can help you experience higher energy levels, better workouts, and a lowered risk of chronic disease.

  1. Sacks FM, Bray GA, Carey VJ, et al. Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates. N Engl J Med. 2009;360(9):859-873. doi:10.1056/NEJMoa0804748
  2. Edinburgh RM, Hengist A, Smith HA, et al. Preexercise breakfast ingestion versus extended overnight fasting increases postprandial glucose flux after exercise in healthy men. American Journal of Physiology-Endocrinology and Metabolism. 2018;315(5):E1062-E1074. doi:10.1152/ajpendo.00163.2018
  3. Mazidi M, Katsiki N, Mikhailidis DP, Sattar N, Banach M, on behalf of the International Lipid Expert Panel (ILEP) and the Lipid and Blood Pressure Meta-analysis Collaboration (LBPMC) Group. Lower carbohydrate diets and all-cause and cause-specific mortality: a population-based cohort study and pooling of prospective studies. European Heart Journal. 2019;40(34):2870-2879. doi:10.1093/eurheartj/ehz174
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