Carbohydrates, carbs, sugar - you’ve heard these terms thrown around in relation to diet but do you really know what they are? Are they good or bad? Depending on what you read, it seems you should either be avoiding them or including them as part of a healthy diet. In order to clear up this confusion and make an educated decision about carbohydrates, it’s best to learn a little about them. Therefore, here’s the lowdown on those important, yet sometimes controversial, carbohydrates.
Carbohydrates: What exactly are they?
Along with the other macronutrients fat and protein, carbohydrates provide energy needed for growth, maintenance, repair and general functioning of the body. Structurally speaking, carbohydrates are molecules made of carbon, hydrogen, and oxygen. The carbohydrates we eat can be divided into three main categories based on the number of carbohydrate units they contains and type of bonds holding these carbon units together.
Simple sugars refer to the monosaccharide and disaccharide forms of carbohydrates. These sugars consist of either one (mono-) or two (di-) carbohydrate units. Monosaccharides are the most basic carbohydrate unit and are found in our diet as glucose, fructose and galactose.
Monosaccharides are used in combination with each other to make disaccharides, as well as longer chains called complex carbohydrates (see below). The most common disaccharides found in our diet are sucrose (glucose + fructose), lactose (glucose + galactose) and maltose (glucose + glucose).
Simple sugars are naturally found in fruits and vegetables (fructose) and dairy (lactose). Sweeteners such table sugar (sucrose), honey (fructose + glucose), molasses (sucrose), maple syrup (sucrose), and agave nectar (fructose + glucose) are all natural sources of these simple sugars. Many pre-packaged, processed foods also contain added simple sugars. To check if the processed foods you eat have added sugars, check the ingredient list for any of the above simple sugars, as well as any syrups (i.e. corn syrup) or ingredients ending in ‘ose’ (i.e. dextrose).
When you hear the term complex carbohydrates it refers to polysaccharides, or a long chains of carbohydrate units. The complex carbohydrates are often referred to as starch as this is one of the most common complex carbohydrates found on our diet. This type of carbohydrate is found in fruits and vegetables, legumes, and grains.
Complex carbohydrates can be refined, meaning all naturally occurring fiber, vitamins and minerals are stripped from the carbohydrate such as with white flour or white rice. Or they can be found in their intact, whole grain form such as with brown rice, wheat berries, oats, pot barley, and whole grain flour.
While technically a polysaccharide like the complex carbohydrates mentioned above, fiber differs in that it is unable to be broken down by the human digestive tract, therefore, it provides no calories.
Despite their lack of digestibility, fiber plays a number of important roles. Two subcategories of fiber, insoluble and soluble, exist and are equally important from a health standpoint. When the soluble fiber found in oats, chia seeds, psyllium husks, legumes and some fruits is combined with water, it forms a gel-like substance. This gel-like substance has been shown to improve blood sugar control by slowing down the release of glucose from the digestive tract into the bloodstream. Along with its effect on blood sugars, soluble fiber also disrupts the absorption of dietary cholesterol and can improve LDL (or “bad”) cholesterol. Some types of soluble fibers are also used by the beneficial bacteria in our large intestine as a food source.
Unlike soluble fiber, the insoluble fiber found in many fruits, vegetables and whole grains does not dissolve into a gel in the digestive tract. Rather, it serves to provide bulk and structure to our stool benefiting our large intestine. Diets high in insoluble fiber are associated with less constipation, diverticular disease and colon cancer. Similar to that of soluble fiber, there are also some types of insoluble fibers that are used as prebiotics, or food for the gut’s beneficial bacteria.
Carbohydrates are only absorbed in their monosaccharide form, meaning all sugars and starches must first be digested into single units to be absorbed in the small intestine. Naturally occurring monosaccharides do not need any further digestion and can be absorbed immediately into the bloodstream. The disaccharide carbohydrate form found in sweeteners (i.e. table sugar, maple syrup) take very little effort on the part of our digestive system to be broken down. As a result, the effect on our blood sugars by these simple carbohydrates (mono- and disaccharides) is quite rapid and significant. A meal or snack rich in simple sugars will cause a higher and faster spike in blood sugars. In short, simple sugars impact blood glucose more significantly. This is particularly troublesome for those with diabetes and insulin resistance but can also have health impacts in non-diabetic individuals.
As mentioned, even complex carbohydrates need to be broken down into their individual carbohydrate units to be absorbed. Due to their longer structure, more time is needed to fully digest and release sugar into the blood. A slower release, and thereby, absorption of sugar causes a less dramatic rise in blood sugars. This helps the body more easily keep the blood glucose levels in a desirable range. If complex carbohydrates are in their unprocessed, whole grain form (i.e. brown rice, pot barley, steel cut oats) as opposed to a refined form (i.e. white flour) the rise in blood sugar will be much slower allowing the body to process and use the sugar in a more sustained way. This slower effect on our blood sugars is largely due to the higher fiber content of these whole grains.
The Glycemic Index: A Different Way to Look at Carbs
It does need to be noted the difference in effects on blood sugars between simple sugars and complex carbohydrates is a generalization and that some prefer to classify dietary carbohydrates based on the glycemic index. The glycemic index was devised to classify carbohydrates based solely on their effects on blood sugar rather than their chemical structure. High glycemic foods influence blood sugars more rapidly while low glycemic foods have less of an effect, independent of whether they are structurally simple or complex carbohydrates. Where the two classification systems (glycemic index vs. simple/complex carbs) conflict is that some foods that would be considered complex carbohydrates have a higher glycemic load (meaning that they affect blood sugar more) than those that contain simple sugars. This difference in carbohydrate breakdown and absorption can be due to a number of factors including food processing (i.e. how refined it is), ripeness, or fiber and fat content of the food. There are a number of great glycemic index resources online that can be used as a guide. This system can be especially useful for those with, or at risk of, diabetes.
Why Do We Need Carbohydrates?
You may think from all the hate carbohydrates get in the media that they don’t serve an important function in the body. Carbohydrates, and particularly glucose, are vital for life. In fact our body’s preferred energy source is glucose. When all other energy sources are present, the body chooses carbohydrates (glucose) as its fuel. Even the other monosaccharides, fructose and galactose, are converted to glucose by the liver.
Glucose is used by the all cells in the body as a primary energy source. This includes your muscles, brain, vital organs, and cells of the central nervous system. Glucose is also stored by our body, in the form of glycogen, to act as an energy reserve for times when we are not eating to keep blood sugars stable and the body running smoothly.
What happens if we eat too much?
Just because carbohydrates are the preferred energy source, doesn’t mean that the body should be given an unlimited supply of them. In the case of carbohydrates, you can get too much of a good thing. When the carbohydrates we eat are digested and absorbed as glucose, it will be first used for energy, that is, if it is needed. If our immediate energy needs have been met, glucose will be used to make glycogen in our liver and muscles. However, your body doesn’t have an unlimited amount of storage capacity for this glycogen. If the glycogen stores are full, the remainder will be converted to triglycerides (a type of fat) and stored in your adipose (fat) cells. Please note that over consumption of calories, in general, will contribute to fat gain, not just those derived from carbohydrates.
Beyond excess carbohydrates building up your fat stores, excess dietary sugars have a negative impact on the cardiovascular system. A diet high in carbohydrates, and particularly refined carbohydrates and simple sugars, is associated with higher rates of coronary heart disease and more negative cholesterol profiles - high triglycerides and LDL (“bad cholesterol”) and lower levels of HDL (“good cholesterol”).
Pro-inflammatory markers have also been found to increase after meals rich in sugars and high glycemic foods. While inflammation is a naturally occurring reaction to infection or injury, if the body is in a state of long-term inflammation, health is impaired. Chronic low level inflammation is thought to play a role in the development of cardiovascular disease, insulin resistance, and cancer. Low glycemic foods cause the body to produce lower levels of these pro-inflammatory substances and is just another reason why they should be encouraged over the consumption of refined grains.
What happens if we eat too little?
As carbohydrates are the preferred fuel source for our cells, the body has devised a back up plan to keep itself up and running if our carbohydrate intake is too low. This back up plan is in the form of glycogen, or the body’s extra glucose supply. The body is very good at keeping itself in a state of homeostasis, and blood sugar control is no different. When carbohydrate intake is low or during a fasting period like overnight, the body will dip into its glycogen stores to provide itself with much needed glucose. This way the body can proceed as normal while it waits to be fed again.
In extreme cases when the body is starved of for a longer period of time, it will switch modes once again and look for another substrate to keep itself running. After glycogen stores are completely used up which can take an average of 8-12 hours (or less if exercising), the body switches to making energy from its internal fat, in the form of ketones, and muscle proteins, which are converted to glucose. The energy derived from fat will first be used in order to protect the wasting of the muscles and organs. The body is pretty smart, isn’t it?
If fat can be used as energy, do we really need carbs?
You may be wondering why we even need carbohydrates if the body can use both fat and protein to function. This is a good question. This point is often debated within the nutrition community. There are individuals who follow a nutritional ketosis diet in which their intake of carbohydrates is so low that their body runs on ketones derived from dietary fat. Not surprisingly, the body can adapt to this type of diet and function well, even in athletic situations. However, once should be warned that this diet is low in fiber and essential vitamins and minerals (found in many fruits and veggies limited on this diet). As such, supplementation of vitamins and minerals is required and regular medical check ups should be considered. Those with type 1 diabetes should never try a ketogenic diet because of the risk of diabetic ketoacidosis, a very serious condition. Individuals considering this diet, whether healthy or not, should discuss such a change with an doctor or registered dietitian with experience in ketogenic diets before undergoing such a drastic dietary change.
Whether or not carbohydrates themselves are essential is debatable in some circles. There is evidence that lower carbohydrate diets do improve metabolic parameters like cholesterol and blood sugars, and that very low ketogenic diets may be beneficial for neurodegenerative diseases. On the other hand, dietary patterns that include fruits, veggies, legumes and whole grains (all carbohydrate source, by the way) are associated with less cancer, diabetes, and heart disease. While it may be the other nutrients like vitamins, minerals, and antioxidants in these foods that lead to these better health outcomes, the presence of carbohydrates certainly does not seem to cause problems if the overall diet is healthy. Populations of people who live up to 100 years of age are not necessarily those who omit carbohydrates from their diets. It is clear, though, that eating excessive amounts of carbohydrates does lead to a number of health problems.
All carbohydrate sources are not created equal and it’s best to remember that the less processed the food, the better it is for you. And this goes for most foods, whether carbohydrate containing or not. Carbohydrates can be part of a healthful diet and they need not be feared. You just need to arm yourself with a little knowledge about the differences between which ones to choose most often and which ones to choose less.
What to learn more nutrition basics? Check out Nutrition 101: Protein