Last week we introduced the bare basics of the carbohydrate world. We saw the basic molecular structure, the difference between the different saccharides, and learned that different carb categories come from different food sources. Today, we will look take a closer look into what carbohydrates actually do in the body and the difference between a simple and complex carb.
Carbohydrates have multiple functions, but we can look at them in four categories: (1)
1. Used directly as energy by cells
2. Stored and used as energy for later use
3. Conversion into fat
4. Prevention of tissue breakdown
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| Carbohydrates: The body's principal energy source |
Let's start with the most common answer, energy usage. Carbohydrates are always being used as energy in our bodies, whether it's exercising or reading this blog, they are in some shape or form in the process of converting or assisting in energy production. The Central Nervous System demands a steady supply of carbohydrates as well as the brain and red blood cells (1), which almost solely uses glucose as fuel (except when extreme conditions demand otherwise). Once a carbohydrate enters your body, at some point in it's lifespan, it will be used as energy or at least aid in this process. If it is not used for immediate energy it will be stored in two forms for future use.
As we discovered in an earlier post (ATP) the body uses ATP to provide the essential energy to function. We also talked about those wonderful processes that convert proteins, fats and carbohydrates into said ATP. Glycolosis converts glucose (remember that giant process?) to this ATP, but one thing I never discussed is how the glucose got there in the first place. You see, it matters not if you eat a complex carbohydrate or a simple one, they all must be broken down into simple sugars in order to begin their journey into the the conversion of energy. We will discuss how this and other digestive properties work down the road as we put all the pieces together, but for now we must understand that once we ingest a carbohydrate, it needs to be broken down into it's most basic form in order to convert into ATP.
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| Yeah, it's pretty complicated.
The first form of energy is an immediate source in the more commonly known, blood glucose or blood sugar. The carbohydrates we ingest will be broken down and circulated in our bloodstream, which are then available for instant usage. The other from is stored glucose called glycogen. This is stored in the muscles and in the liver, until it is called upon once the instant source of blood glucose is used up. The process of Glycogenolysis, converts this glycogen into glucose and is then ready to head through the energy conversion process. This process is most often used in intense exercises such as; weight lifting, sports and manual labor.
Carbohydrates are used every moment of the day, but as I said earlier, they are heavily used during moderate to intense physical activity. This happens through an anaerobic process, meaning oxygen is not needed for energy conversion. Generally, any challenging activity lasting from 30 to 90 seconds, weight lifting being the best example, relies on carbohydrates for it's primary energy source. This is where the stored glucose comes into play because as we continue to exercise we need more energy from glucose, thus the stored glycogen in the muscle and liver release and allow us to continue to exercise, but of course that won't last forever, which is why you will see a decrease in performance after each hour of exercise (2). This is the exact reason why athletes, marathoners and weight lifters perform some sort of "carb load" at some point before their event so they can have a steady supply of carbohydrates for energy. Even though longer lasting activity relies on lipids as it's primary fuel source, we have a saying in the physiology world "fat burns in the flame of carbohydrate" meaning, carbohydrates are needed even if they are not the primary fuel source.
A steady supply of carbohydrates allows the energy conversions to occur at a normal pace, but what if there were no carbohydrates to convert? Our bodies will find a way to make energy as long as there is some form of raw material to do so. Keeping a healthy amount of carbohydrates in our bodies is far more important than just for exercising, they help prevent catobolism and ketosis (leading to ketoacidosis) (1). In extreme cases, starvation for instance, the body will break down muscle tissue in order to convert it into amino acids, which can then be put through one of the energy cycles. The problem is when our bodies enter this catabolic state, it literally eats itself away (hence the withering of a person suffering from starvation) which can have many negative long term health effects. When our bodies use stored fat as an energy source for it's primary fuel, ketone bodies accumulate and can also have negative affects, from ketoacidosis or having a higher blood pH (that's bad). (2)
Finally, when the liver glycogen stores are full, the excess glycogen will be converted into fatty acids, which will then hitch a ride in the bloodstream and be dropped off at the various Adipose tissue in the body. Of course, if this process is utilized too often, total body fat increases and obesity can occur. This very concept is why carbohydrates have become the enemy in the diet world. The hundreds of carb-free diets and carb restricted rules have taken over, but only because many do not know the basic functions of carbohydrates. The major problem is not so much the carbohydrates, but rather how easily they are obtained and how much you can ingest before you realize it. Ever take a look at the total carbohydrates on a big bagel or muffin? They can have up to 40-50g of carbs. According to the 2010 US dietary guidelines, Americans should be getting 45-60% of their total calories from carbohydrates. At 200 calories (50g x4 kcal) that would be about 10% of your daily caloric intake right there, so imagine if you had a glass a juice and other breakfast foods to go with that. We will discuss calories and percentages of, and examples in later blogs, but just remember it is very easy to consume excess carbohydrates without ever knowing it.
Now we have a general understanding of what some typical carbohydrates are in the everyday world and their basic functions in the body. In the next blog we will differentiate between simple and complex carbs, how they are broken down in the body and the effects they have on our various physiological functions (insulin and blood sugar). The carbohydrate is an essential component of our everyday lives and I think after the next installment we will be able to fully appreciate them, now that we understand their roles and the differences that separate them.
Thanks for reading!
“Life is largely a matter of expectation. ” - Homer
*I am not a doctor or a licensed physician. I am in no way diagnosing anything and recommend that you speak to your physician before making any medical/supplemental/nutritional decisions.
*I am not a registered nutritionist or dietitian. The information presented is for education purposes only.
1. MxArdle,W. Katch, F. Katch, V. Sports and Exercise Nutrition 4th edition (3-19 & 147-161) NY: Lippincott Williams & Wilkins
2. Powers,S. Howley, E. (2007) Exercise Physiology Theory and Application to Fitness and Performance 6th edition (478-482) NY: McGraw Hill
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