Dietary Carbohydrate: Facts and Misconceptions

Blog Post

Stephen W. Farrell, PhD, FACSM
The Cooper Team
March 30, 2022
Low carb/ketogenic diets have been cycling in and out of popularity for the past half century! During that same time period, obesity rates have skyrocketed worldwide.

With that in mind, this is a good opportunity to discuss facts as well as misconceptions regarding dietary carbohydrate. First, the basics: carbohydrate is one of 6 essential nutrients required by the human body for survival. All carbohydrates contain 4 calories per gram. During the digestive process, dietary carbohydrate is broken down into glucose, which then leaves the intestines and enters the blood. Glucose is a major energy source for all cells of the human body; particularly the brain and spinal cord as well as red blood cells. When the body consumes too much carbohydrate, some of the excess is stored as glycogen in muscle and liver cells. Glycogen is best thought of as tens of thousands of glucose molecules bonded together. When muscle and liver cells reach their capacity for storing glycogen, the remainder of the excess carbohydrate is converted to fatty acids and stored in adipose (fat) tissue. So far, nothing that has been stated is the least bit controversial. You will find this basic information in all nutrition and medical textbooks.

Now let’s dig a little deeper. There are two broad categories of dietary carbohydrate; simple and complex. Simple carbohydrates are synonymous with simple sugars, which are found in high concentrations in foods and beverages such as non-diet soda, candy, syrup, sports drinks and energy drinks, doughnuts, pastry, cookies, and cakes. These products are often referred to as ‘empty calorie’ foods; which simply means that they have very low nutritional value. You just won’t find many vitamins, minerals, phytochemicals (non-nutrients in plant-based foods that help prevent disease) or much fiber in most foods and beverages that are high in simple carbohydrate. While lacking in fiber, 100% fruit juice is a notable exception to this rule! Kids and adults should limit their 100% fruit juice intake to no more than 8 ounces (1cup) per day though.

Complex carbohydrates are plant-based foods, and include things such as fruits, vegetables, whole grains, and legumes (beans, peas, and peanuts). Unlike simple carbohydrates, complex carbohydrates pack quite a wallop nutritionally speaking. They are loaded with fiber, vitamins, minerals, and phytochemicals. With the exception of fruit, most complex carbohydrates are also a significant source of dietary protein. Most people are very surprised to learn that! So whenever we speak of dietary carbohydrate, it’s very important to distinguish the simple from the complex.

So how much dietary carbohydrate should you consume each day?

The answer to that very important question depends on the individual. The current RDA for carbohydrate is 45-65% of total daily calories; with most of that in the complex form. If you have metabolic syndrome, it is generally recommended that you consume the lower end of the recommended range, i.e., closer to 45%. Those with metabolic syndrome or type 2 diabetes should check with a health care provider with an expertise in nutrition; preferably a Registered Dietitian (RD) or Certified Diabetes Educator (CDE). On the other hand, if you are very highly physically active each day, you may need to consume the upper end of the recommended range. Unless you have a particular health condition, the overwhelming majority of qualified health professionals recommend that you stay within the recommended range of 45-65% of total daily calories. You may be wondering at this point how many total calories that you should consume each day. That number is determined primarily by your age, sex, height, weight, and physical activity level, as well as your goals. You can get a good estimate of your total daily calorie requirement by using this link. Please note that the estimate is based on the goal of maintaining your current body weight. If you wish to lose weight, you should subtract about 300-500 calories per day from the estimate, and you should also plan to become significantly more physically active.

Can too many carbs make you fat?

Sure. Our body weight status is dictated by the number of calories we consume each day versus the number of calories that we expend. Consuming too much of anything (even the healthy stuff!) can result in weight gain if we wind up consuming more calories each day than we expend. That’s why it’s important to focus on the quality as well as the quantity of carbohydrate that we take in each day. By limiting simple carbohydrates and emphasizing complex carbohydrates in our diet, we significantly decrease our risk for developing metabolic syndrome and type 2 diabetes, as well as cardiovascular disease, diverticulitis, and some cancers. These risks can be further decreased by becoming more physically active and achieving a reasonable body weight.

What about very low carb diets?  These ‘ketogenic’ diets recommend getting only ~10-15% of total daily calories from carbohydrate, which generally speaking, is not a good idea for most people. Such an approach will likely lead to short-term weight loss, but there is little to no evidence that these diets result in long-term weight control or improved long-term health for most individuals. The very low carb diet has been around for over 50 years and tens, if not hundreds of millions of people have tried it. If this approach actually resulted in long-term weight control for most individuals, then why are over 70% of American adults currently overweight or obese?

So, to summarize:

  • Dietary carbohydrate is essential to human survival
  • Dietary carbohydrate exists in two broad categories; simple and complex
  • Most simple carbohydrates are nothing more than empty calories        
  • Complex carbohydrates are plant-based foods that are loaded with nutrients, fiber, and phytochemicals.  Most complex carbs are also a good source of protein.
  • All dietary carbohydrate is converted to glucose during digestion
  • The RDA for carbohydrate is 45-65% of total daily calories
  • Individuals wishing to lose weight in a healthful manner should plan on decreasing their calorie intake by 300-500 calories per day and should also plan on becoming more physically active
  • There is little to no scientific evidence that very low carbohydrate diets lead to long-term weight loss or improved long-term health!

2020-2025 Dietary Guidelines for Americans: Executive Summary


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