Nov. 14. 2014
Written By:
McKel (Hill) Kooienga
McKel Kooienga, MS, RDN, LDN

McKel Kooienga, MS, RDN, LDN

Founder of NS and Creator of The Method

Dietitian Nutritionist McKel answers what are carbohydrates and explains food sources and the function of carbohydrates.

From a dietitian’s perspective, consumption of all three macronutrients – protein, fat, and carbohydrates – get taken to extremes when it comes to our health and especially when talking about weight or fat loss. However, all three macronutrients are incredibly important and vital to our health.

With that said, far too often you hear extreme examples of macronutrient consumption like no-carb and high-carb diets, both of which have no middle ground, little flexibility, and limited longevity. This post will explain what carbohydrates are, how they function in our bodies, why you need carbohydrates, healthy food sources of carbohydrates, and storage of carbohydrates.

What are carbohydrates made of?

Biologically speaking, carbohydrates are large molecules or macromolecules containing hydrogen, oxygen, and carbon atoms. Carbohydrates are typically stated as a saccharide, which means “sugar”. Saccharides (a.k.a. carbohydrates or sugars) are divided into four types: monosaccharide, disaccharide, oligosaccharide, and polysaccharide.

The Latin prefix of each type of saccharide explains how many monosaccharides (simple sugars) are in each saccharide. Mono= 1, dia = 2, oligo = 3-9, and poly = more than 10. Monosaccharides and disaccharides like fruit or simple sugars are digested very quickly, while oligosaccharides and polysaccharides like higher fiber or starchy vegetables digest more slowly.

Monosaccharides are the building blocks of creating dia-, oligo-, and polysaccharides. The types of monosaccharides are: 1) glucose, 2) fructose, and 3) galactose.

Some of many examples of dia-, oligo- and polysaccharides are :

  • Table sugar, also known as sucrose, is a disaccharide made from glucose + fructose.
  • Milk sugar, also known as lactose, is a disaccharide made from galactose + glucose.
  • Starch, glycogen, amylose, and inulin are all examples of polysaccharides, starches, and fibers.
  • Fructooligosaccharide (FOS) is an oligosaccharide found in veggies and fruits.

Mono-, dia- oligo-, and polysaccharides are the basic building blocks of carbohydrates, but carbohydrates are also grouped into refined, simple, and complex carbohydrates. Often refined and simple carbohydrates are used synonymously, but they actually have different meanings. A “refined” carbohydrate, like table sugar or refined grains, has been stripped of its nutrition through processing and therefore digests quickly in the body which causes blood sugar to rise. However, a simple carbohydrate doesn’t always mean it’s been refined. Fruit is an example of a simple carbohydrate due to its sugar content and how quickly the body digests it and is far from being refined.

Whole food sources of carbohydrates

  • Fruit
    • Lower sugar picks: green apples, cranberries, lemons, limes, raspberries, acai berry, goji berries
    • Higher sugar picks: bananas, papaya, mango, pineapple, dates
  • Dairy (although on NS I don’t use dairy)
    • Milks, yogurts, cheeses, etc.
  • Vegetables
    • All vegetables are carbohydrates! Yet, negligible amounts per serving (sometimes less than 5g)
  • Starchy Vegetables
    • Organic corn, sweet potatoes, potatoes, peas, green beans
  • Beans, pulses, legumes
    • Lentils, chickpeas, black beans, split peas, etc.
  • Grains
    • Quinoa, rolled oats, millet, amaranth, wild rice, basmati rice, gluten-free breads, etc.

A whole foods lifestyle is all about focusing on all forms of carbohydrates, especially those that are closest to their natural form like dark leafy greens, fruits, grains, beans, and legumes. There is such thing as enjoying carbohydrates, using them strategically when your goals change for fat or weight loss, and enjoying a variety of them daily to meet your needs.

What are carbohydrates used for?

Carbohydrates are our body’s preferred use of energy. Our brains, muscle tissue, and cells all utilize carbohydrates in different amounts and ratios. Each gram of carbohydrate is roughly four calories or units of energy.

How your body uses carbohydrates:

  • The brain uses about 120 grams of glucose per day. The preferred energy source for the brain is solely carbohydrates. In fact, the brain utilizes about 60% carbs at a resting rate (i.e. when you’re just sitting around!). The body can create glucose even when there is little present from food.
  • Muscles, including skeletal muscle and also muscles like the heart, use carbohydrates as fuel and also ketone bodies and fatty acids. Muscle has the unique capability to store excess carbohydrates of up to 1200 kcal (kilocalories) that are called glycogen. Because it can store glycogen, muscle is always “ready” for action, but when at rest your muscle prefers to burn or use fatty acids.
  • Fat cells store excess carbohydrates (triglycerides) as adipose tissue for later use of energy. These triglycerides can be used for energy in multiple ways through different conversion processes. Because excess carbs can be stored as fat, if your goal is maintaining a healthy weight or achieving weight loss you should aim for the delicate balance of trying not to overconsume carbohydrates but ensuring you consume enough for your body’s needs.
  • Kidneys use carbohydrates to perform many processes that help our bodies get rid of what we don’t need and excreting as urine. Kidneys also filter and reabsorb nutrients and minerals we can use again or are in need of like sodium, glucose, etc.
  • The liver uses glucose for energy to process and metabolize everything we put into our bodies from glucose, amino acids, and fatty acids.

How are carbohydrates digested?

Carbohydrate digestion starts in the mouth as all digestion does, but especially with the digestive enzyme amylase that helps to specifically breakdown carbohydrates. Carbohydrates then go into the stomach where stomach acids meet with chyme (mixed food) and further break down before entering into the small intestine, where again digestive enzymes are released that break down carbohydrates into monosaccharides to be absorbed in the small intestine.

Ultimately, glucose enters the liver where it distributes the energy by either storing it into fat cells or utilizing it for immediate energy in other cells of the body. All other carbohydrates that are not absorbed in the small intestine reach the large intestine and colon. These are fibrous carbohydrates that are partially digested by bacteria. Fiber can’t be digested or absorbed like other carbohydrates but helps contribute to the bulk of our stools which is an important part of our digestive health.

How many carbohydrates do you need in a day?

Technically, none. The human body can survive off of other energy sources like fatty acids and amino acids, BUT it does prefer carbohydrates, and most dietitian nutritionists including myself would recommend that too. How many carbohydrates you need depends on your genetics, age, gender, lifestyle, activity level, injuries, disease states, etc., and all play a role in how many carbohydrates your body needs to fuel. Aim for consuming complex carbohydrates like those outlined earlier in the post rather than refined carbohydrates.

There are a time and place for refined and simple carbohydrates, but being able to control refined and simple carbohydrate intake and use them strategically is key. Carbohydrates can be used strategically by timing carbohydrate intake with your workout and training schedule, keeping in mind the rest of your meal plan and total macronutrient intake. This kind of carbohydrate consumption to meet training or weight loss goals can be fine-tuned with the help of a dietitian nutritionist professional.

Are low carb diets bad for you?

I’m asked so often what my thoughts are on some of the trendy carb-focused diets. In a nutshell those questions can generally be answered with this: If a diet is something that can’t be maintained, can’t be envisioned in 5 years as part of your life, socially isolates you from others or activities you enjoy, or is harmful to your mental/physical/emotional health, then it is not a healthy lifestyle.

Many diets buzzed about in the media and in social circles are either high carbohydrate promoting or low carbohydrate promoting with very little diets in the middle ground. Human bodies can’t completely abstain from carbohydrates. I simply ask this, next time you try to “go low carb” or go “80-10-10” envision yourself in 5 years. If it’s something you can effortlessly and enjoyable maintain, then go for it. If not, reevaluate the reasons why following that dogma in the first place.

If you’re wondering what these diets are all about, I’ve outlined the basics and my take on popular diets.

South Beach Diet, Atkins, Duncan diet, etc.

Promote periods of time with little to no carbohydrates (other than vegetables) and heavy protein and fats followed by introducing a maintenance phase of some sort. These are successful for many up front, but long-term use of these lower carbohydrate diets most likely result in weight regain. Also, these diets don’t necessarily promote whole foods as they’re very focused on grams of carbohydrates coming from any source, which means artificially sweetened and processed foods as well.


This is one of the more radical diets I’ve coached clients recovering from. 80% of the diet is carbohydrates, 10% is fat, and 10% comes from protein. Food sources are all vegan and mostly all raw foods only.

As you can see this diet is abundant with fruits and vegetables, but lacks the variety with other foods which translates into nutrients. Advocates of this diet claim they can receive enough and ample amounts of nutrition through this diet, which may be the case, yet one would have to eat extremely large amounts (several pounds at one sitting) of these foods to obtain enough nutrition. The sheer volume and burden on your digestion may cause some people to feel bloated all the time, have loose stools, lack of energy, etc. I’ve had many clients “recover” from this type of diet and all claim they’re so much happier to be eating more varieties of foods.


Generally means consuming less than 20% of your daily calories from carbohydrates, but there are so many variations of low carb dieting. In a nutshell, low-carb diets limit or eliminate all carbohydrate-rich foods and focus on fats and proteins. The downside is that this diet doesn’t have a “rule” or guideline about what foods to consume and most often people find themselves eating “low carb” or “sugar-free” “health” foods which are far from healthy and loaded with processed fats, sugar alcohols, and artificial ingredients. Most lose weight in the short term following these diets, but only to have their weight creep back up when they start consuming more carbohydrates again. However, some enjoy this way of eating as a lifestyle.


Oftentimes means consuming less than 30 grams of carbohydrates total per day. There are variations of this diet, but it’s most notably used therapeutically for those suffering from seizures although many fitness and bodybuilding community members utilize this for their “lifestyle”.


There are many variations of this movement, but limiting carbohydrates is central since grains, legumes, and dairy are eliminated. I’m actually a fan of the paleo movement in the broader sense that it’s helped people focus more on the quality of food and where it’s sourced. What I’m not a fan of is recommending everyone to completely eliminate grains and legumes as many people and their digestive systems can thrive by incorporating these foods.

Diabetes and types of dysfunctions with carbohydrate metabolism

When I used to work clinically, it was part of my daily routine seeing patients who had diabetes or with a pre-diabetic diagnosis and lab work. This is not something that just presents itself in clinical settings. There are millions of people walking around daily with diabetes and surprisingly some don’t even know it. Below is an explanation of diabetes diagnoses and how diabetes can manifest in the body:

  • Pre-diabetes: Pre-diabetes means your blood sugar is higher than normal or higher than it “should be”, but not yet high enough to be diagnosed with type II diabetes. When clients present me with pre-diabetic lab work, this is the time more than ever to drastically change lifestyle habits and get healthy once and for all before type II diabetes results, which is much more serious.
  • Diabetes: There are two main forms of diabetes, type I and type II. Type I is the less common diabetes resulting from the hormone insulin not being produced by the body, i.e. energy from sugar and food isn’t being converted like normal. Type II is more widely spread and is the result of high blood sugar coupled with insulin resistance (and also not enough insulin). Insulin resistance is when your pancreas, which makes the hormone insulin, makes extra to make up for the high blood sugar, but over time can’t make enough insulin to keep blood sugars at normal levels.
  • Gestational diabetes: Gestational diabetes typically happens in pregnant women after 22 weeks, and this diagnosis doesn’t mean that you had diabetes or that you will have diabetes after you give birth. Lifestyle is an incredibly important factor in managing this and all above.

How to improve insulin sensitivity

Ideally, the body will have a normal insulin “sensitivity”, or will react well and in tune with your body and the number of carbohydrates it encounters versus being “resistant”. Low insulin sensitivity = higher insulin resistance, i.e. your body needs more insulin from your pancreas to keep blood sugars stable. Long-term insulin resistance can result in type II diabetes.

There are several things to do to overall improve insulin sensitivity in the body. First and foremost, the best way to improve insulin sensitivity is to change the diet by consuming more complex carbohydrates in comparison to refined or processed carbohydrates (think of more vegetables, fruits, and fiber and less white sugar, refined carbohydrates, and processed foods). Another effective way to improve insulin sensitivity is to get up and move! That’s right, commit to an exercise regime of both cardio and weight resistance exercises and do it consistently. Lifestyle factors such as stress management and getting enough sleep are also important to improve insulin sensitivity.

More resources for your reading pleasure on all things carbohydrates

Krause Nutrition textbooks

Basic Medical Biochemistry

Nutrition Therapy and Pathophysiology

Advanced Nutrition and Human Metabolism