"Is butter a carb?" - Regina George (Mean Girls)
Carbohydrates have been under a lot of fire lately. Mention “carbs” and things like pasta, baked goods, and bread will come to mind. While swimming in childhood, we would talk about “carb loading” before a big swim meet. This referred to a giant plate of spaghetti, which was usually followed by a second. We did this because of the tie between carbohydrates and their relation to energy. Carbs equal energy. After all, eat your whole bucket of Halloween candy and you will feel a burst of energy, fleeting as it may be. But what exactly is a carbohydrate? Are all carbs the same? How does our body process them? Where do they come from? Let’s take a look at these.
All About Carbs
Carbohydrates are an important part of our diet. While we can derive energy from all macronutrients, carbohydrates are our main source of energy. It is recommended that 45-65% of our diet come from carbohydrates with at least half of these coming in the form of whole grains. This amounts to around 900-1800 calories per day from carbohydrates. They come from a variety of sources, including grains and cereals, fruits, vegetables, dairy, and the obvious table sugar. Carbohydrates are sugars. They can be thought of as chains of sugars. Where they differ is in the sugars that are linked up and the length of the chain. Dietary carbohydrates are made up of chains of hexose sugars, comprised of 6-carbon atoms which form a ring, though they are often drawn as a straight line.
Monosaccharides
Monosaccharides are as simple as sugars get. They consist of a single hexose ring. In order to be used for energy, larger chains are broken down to monosaccharides during the process of digestion. The most naturally occurring dietary monosaccharides include fructose, galactose, mannose, and glucose. There are other monosaccharides, but they either do not occur naturally or are only found in very small quantities in nature. Glucose is not only the most abundant carbohydrate, but it is the most central to energy metabolism in a pathway known as glycolysis. The other dietary monosaccharides are converted through enzymatic reactions into glucose-derivatives to enter the glycolytic pathway. Fructose is especially abundant in honey and fruits. Galactose can be found in dairy, avocados, and sweet beets. Mannose, though important in many reactions, can be created from glucose by the body.
Disaccharides
Disaccharides, as you might guess, are made up pairs of monosaccharides. Sucrose is made up of fructose and glucose. It is found naturally in plants, and when it is refined it becomes table sugar that goes into all those cookies and candies. The bond between fructose and glucose is severed by an enzyme in our small intestines aptly named sucrase. Maltose, which is a disaccharide of two glucose molecules, is found in malt products. It is broken down by the enzyme maltase. Finally, lactose, a disaccharide found abundantly in milk products, is well-known to anyone who lacks the enzyme lactase, which normally breaks this disaccharide down into galactose and glucose. Deficiency of this enzyme is what makes people with lactose-intolerance symptomatic after consuming milk products laden with lactose.
Oligosaccharides and Polysaccharides
Oligosaccharides are chains that are 3-10 sugars in length, whereas polysaccharides are, chains that are longer than 10 monosaccharides long. These form plant and animal starches, including fiber. Those starches that are digestible are broken down into di- and trisaccharides by the enzyme amylase, which is found in saliva. This is why the longer you chew on a saltine cracker the sweeter it will taste. These smaller sugars are then further broken down into monosaccharides in the small intestine where they will be absorbed into the bloodstream. Our bodies are able to link glucose molecules in extensive chains to form glycogen, which is stored in muscle and the liver.
Blood Glucose
Anyone who has a family member or friend with diabetes knows that they are required to check their blood sugars frequently. But what are they measuring? Glucose is the sugar that is being measured in the blood, which is why the machine they use is called a glucometer. In an effort to maintain homeostasis, our bodies regulate blood glucose levels so that they do not go too low (hypoglycemia) or too high (hyperglycemia). Blood glucose levels are very important to maintain, because the primary source of nourishment for the brain is glucose from the blood. These two processes are primarily regulated by insulin, which lowers blood glucose levels, and glucagon, which causes an increase. Blood glucose spikes after each meal, causing a release of insulin, that leads to the blood glucose falling again.
You might be asking yourself what keeps the blood glucose levels normal in the time between meals, and especially during the time that we sleep. If we are not eating food to get more glucose, where is it coming from? In fact, there are three main sources of glucose in the body. The preferred and primary source of glucose is through the food we eat. Dietary sources of glucose cause an increase in blood glucose after meals. In between meals when this level begins to fall, normal blood glucose levels are maintained by glycogen in the liver. As mentioned above, glycogen is a polysaccharide made up of many glucose molecules. Our bodies store excess glucose in the liver as glycogen, which is released in between meals to maintain normal blood glucose levels. Glycogen stores are normally enough to last for several hours between meals. However, when we are sleeping or during other periods of fasting, those stores begin to run low. At this point, our body relies heavily on a process called gluconeogenesis (literally “creation of new glucose”). This process uses energy to create glucose from certain amino acids, breakdown of fats, and other non-carbohydrate carbon-containing molecules.
Simple vs Complex
Yet another way that carbohydrates are classified is simple and complex carbohydrates. You may have heard these terms before, but wondered what exactly it meant. What this really tells us is how quickly the carbohydrate in question will make your blood glucose rise. If it gives you a fast, high spike in blood sugar then it is classified as a simple carbohydrate. This is the bucket of Halloween candy we discussed. It gives you that quick “sugar high” that comes on quickly, but causes you to crash relatively soon after. This is compared to carbohydrates that have a more sustained release into the bloodstream, which will lead to less of a peak and more of a sustained and even blood glucose level.
Why is this important? Well, every time you have a sharp spike in blood glucose your body reacts to correct this by releasing a larger dose of insulin from the pancreas. Insulin causes your cells to absorb the glucose that is saturating your blood. As the glucose shifts into your cells, your blood glucose level drops. The problem here is that as this happens more and more not only does your pancreas have to work harder to churn out insulin, but the insulin receptors on the cells become less sensitive to insulin. As their sensitivity decreases, it takes more and more insulin to get those receptors to cause the cell to absorb the glucose, which in turn causes your pancreas to make ever larger doses of insulin. Eventually your pancreas will be pushed to its limits and will not be able to keep up with the demand. In fact, it may even burn out, so to speak, and begin to release less and less insulin. This is is how people acquire type 2 diabetes mellitus.
So it’s important to know what carbohydrates are simple and those that are complex. You don’t have to completely eliminate carbohydrates from your diet. The goal is to shift the intake of your carbohydrates to one that has a higher composition of complex carbohydrates compared to simple carbohydrates.
Simple Carbohydrates
Refined sugar
White flour
White rice
White and brown sugar
Molasses
Syrups
Honey
Fruit juices
Regular soda
Milk products
Complex Carbohydrates
Whole wheat
Brown rice
Oats
Quinoa
Corn and cornmeal
Barley
Whole fruit
Nuts and seeds
Legumes (black beans, chickpeas, lentils, etc)
Vegetables (carrots, asparagus, broccoli, leafy greens)
Starchy vegetables (potatoes, green peas, squash)
Fiber
Some of the polysaccharides that doesn’t always get a lot of attention are those that are classified as fiber. You may see packaging in the grocery store for breads or other grain-based products that claim to be “a good source of fiber.” But what is fiber and why is it important?
Fiber, also known as “roughage,” refers to those polysaccharides that are indigestible in the human digestive tract. Because of how the bonds or links between the different molecules are sugar are structured, there are no enzymes created by our bodies or the bacteria that live in our digestive tract that can break down those long chains into monosaccharides for us to absorb. So, if we are not absorbing these sugar to convert them into energy, how are they of any benefit to us?
Fiber comes in two forms: soluble fiber and insoluble fiber, and both play different roles within our digestive tract. Soluble fiber, as you might guess, are those that can be dissolved in water. This is the type of fiber that helps to lower LDL cholesterol, and can be found in oats, peas, beans, apples, citrus fruits, carrots, and barley. Insoluble fiber, such as cellulose, do not dissolve in water, and therefore add bulk to stool and aid in digestion. Foods like whole wheat flour, wheat bran, nuts, beans, and many vegetables are rich in insoluble fiber. Both types of fiber are involved in maintaining control of blood glucose.
So, how much fiber do we need? Turns out recommendations vary depending on your sex and age. Men are recommended to consume 38 grams/day when 50 years and younger and 30 grams/day when over 50 years. Women require a little less at 25 grams/day when 50 years and younger and 21 grams/day when over 50 years.
| Women | Men | ||
|---|---|---|---|
|
50 years and younger |
Over 50 years |
50 years and younger |
Over 50 years |
|
25 grams/day |
21 grams/day |
38 grams/day |
30 grams/day |
Other Indigestible Sugars
I wanted to talk briefly about other indigestible sugars. This is where some artificial sweeteners, such as sucralose (Splenda) come into play. Because of how their molecules are arranged, there are no enzymes in the human body or the bacteria within the gut that can break these down into digestible sugars to be absorbed. Therefore, it provides the sweetness without the energy. The danger here with some of these indigestible sugars is that if enough of them are consumed it will create a large solute load in the gut, causing water to shift through osmosis into the digestive tract to dilute this. This shift of water into the digestive tract can lead to diarrhea. So, beware.
Whole Grains
The anatomy of the a whole grain helps to demystify what makes brown rice a whole grain and white rice a refined grain. Through the process of refinement the bran and germ are removed from the whole grain, leaving the endosperm. In order to understand what makes the refined grain less healthy and less complex than the whole grain, we must discuss the various parts of the whole grain and what they contain.
Bran
Starting on the outside of the whole grain, we encounter the bran. The bran is the shell that encompasses the seed of a whole grain. It is rich in vitamins, fiber, and minerals. This fibrous shell is rich in B vitamins: thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), and folic acid (B9). Important minerals found in bran are manganese, magnesium, selenium, phosphorous, iron, zinc, copper, and calcium.
Endosperm
Just under the bran is the endosperm. This makes up the majority of the grain, but also contains the least amount of nutrients. Because it’s main purpose is to provide the germinating seed with a source of energy, it contains mainly energy-rich starches. Otherwise, it has very little to offer in the form of nutrition. This is the portion that remains after a grain has been processed and refined.
Germ
The most internal portion of the grain is the germ, which if left to grow is where the plant would originate. The germ contains many nutrients, antioxidants, unsaturated fats, B vitamins, and vitamin E.
Whole Grains
Amaranth
Barley
Brown rice
Bulgur (cracked wheat)
Corn products (tortillas, cornmeal)
Farro
Flaxseed
Millet
Oats
Quinoa and quinoa pasta
Rye
Spelt
Wheat berries
Whole wheat couscous
Whole wheat pastas
Wild rice