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The Carb Course

Carbohydrates can get a bit of a bad rep. And sure, people can certainly overdo it when it comes to carbohydrate consumption. But, we need carbs. They’re at the root of our physiology and are instrumental to function. So, read on if you want to really understand carbs a bit more.

Carbohydrates are broken down to supply glucose, which is in turn used to produce energy in the form of ATP (adenosine triphosphate). ATP drives most of the cellular processes that keep us alive. Glucose is preferred energy source for body cells, and it is the ONLY energy source for red blood cells. Believe it or not, the back bone of DNA is actually made of sugar!

Our cells require a constant source of energy, which is provided primarily by glucose, secondarily by fat and rarely by protein. Most of our glucose comes from dietary carbohydrates or stored carbohydrates (in the form of glycogen, which will be discussed later in this discussion).

Sugars, starches and fiber are all examples of carbohydrates.  If you care to know a bit more, I’ve broken it down below.

Carbs can be divided into two major groups based upon their size:

  • Simple carbohydrates:
    • Monosaccharaides (single sugars)
      • Glucose – (aka dextrose) is THE essential energy source for all body functions. It rarely occurs in foods, and rather, is the byproduct of sugar breakdown.
      • Galactose – this is the sugar found in milk, but rarely is found in other foods in this form. Galactose is an essential component in galactolipids, which comprise the myelin sheath that surrounds our nerves.
      • Fructose – this is the sweetest of the sugars; it’s found in fruits, honey, agave and high fructose corn syrup.
    • Disaccharides (two sugars, formed by bonding two monosaccharides):
      • Sucrose – this sugar is comprised of glucose and fructose and is table sugar, which is made from sugar cane and sugar beets. 
      • Maltose – this sugar is comprised of two glucose molecules, and rarely occurs in foods. Rather, it is produced as starches break down (e.g. in digestion or in fermentation).
      • Lactose – this sugar is comprised of glucose and galactose and is the primary carbohydrate in milk.
  • Complex carbohydrates:
    • Polysaccharides (groups of single sugars bound together):
      • Starch –plants store glucose in the form of starch. When ingested, starch is digested into glucose.
        • Resistant Starch – this substance acts like fiber. It resists digestion and absorption in the small intestine. It acts as a prebiotic and is a glucose source for the bacteria in the colon. Sources include unripe bananas and plantains and cooked potatoes.
      • Glycogen – the human body synthesizes this form of sugar, which can be stored in the liver and muscle tissue. Stored glycogen is release into the blood to raise blood sugar when blood sugar levels drop. Glycogen does not naturally occur in food, as plants to NOT synthesize glycogen. Furthermore, glycogen is rapidly metabolized, so most animal products no longer contain glycogen by the time they are consumed.
      • Fiber – the structural parts of plants (e.g. stems, roots, leaves, skins) are made of fiber. Fiber differs from starches because the bonds between their sugars cannot be broken down by digestive enzymes. This is why fiber helps digestion – it remains intact until it reaches the colon, where it is broken down by bacteria. There are two main categories of fiber:
        • Soluble Fiber – as its name implies, soluble fiber can dissolve in water and forms a viscous, gel-like product. It is fermentable and is easily digested by the bacteria in the colon. It is found in oats, barley, oats, legumes and fruits. Soluble fiber binds with bile in the intestine, which helps the body to excrete broken-down hormones. It slows transit time through the upper GI tract and helps to lower blood glucose levels by slowing down glucose absorption from the small intestine. It also increases the water intake of stool, thereby acting as a stool softener.
        • Insoluble Fiber – because this form of fiber does not dissolve in water, it does not form gels. It is found in whole grains, seeds, nuts, vegetables (cabbage and bruseel sprouts, in particular) and legumes. Other food component sources include psyllium and cellulose. It can increase the bulk of stool and can improve bowel movements by acting as a “broom” to “sweep” the lining of the colon.

As I’ve stated before, our bodies use glucose for energy. The goal of digestion is to break down disacchardies and starches into usable monosaccharides (glucose). This is why simple sugars are so readily absorbed – they don’t need to be broken down! Carbohydrate digestion begins with the chemical activity of enzymes in the mouth as well as the mechanical action of chewing. When food reaches the stomach, the acids in the stomach deactivate the enzymes from the mouth, thereby halting carbohydrate breakdown. As the food progresses to the small intestine, it is acted on by enzymes from the pancreas and the lining of the small intestine. Glucose is then absorbed through the small intestine and raises blood sugar. Once these simple sugars have been absorbed, they can either be used to create to ATP, or it may be stored as glycogen in the liver or muscle tissue, or converted to fat.  Within 1-4 hours after a meal, starches and disaccharides have been digested and monosaccharides have been absorbed. The remaining fiber will move into the colon and will be fermented by the resident bacteria (this is where gas is formed!)

When we consume more carbohydrates than our body needs, it will store them in the form of glycogen in the liver or muscles (1/3 of our stored glycogen is in the liver, while the other 2/3 is stored in the muscle tissue). If our glycogen stores are full, the excess carbohydrates will be converted to fat and will be stored. Our bodies can store approximately 500g of glucose in the form of glycogen (this is 2000 calories – a LOT of energy!). And of course, frequent over-consumption of carbohydrates can lead to loss of blood sugar control. This obviously is a relatively complex topic, but here’s what you need to know: 

  • Glucagon is the hormone that stimulates the liver to break down glycogen and to release glucose into the blood. It’s secreted by the pancreas when blood sugar falls.
  • Insulin is the hormone that enables cells to take up glucose from the blood. It’s secreted by the pancreas in response to high blood sugar. When we have chronically high levels of blood glucose, insulin receptors can fail to respond to insulin (thereby leading to “insulin resistance”). In these cases, blood sugar remains high, and this causes systemic inflammation, oxidative stress and damage to blood endothelium. 
  • Cortisol is the stress hormone and it leads to blood sugar release from liver glycogen in moments of stress. So, chronic stress can lead to chronically elevated blood sugar, which can ultimately affect insulin sensitivity.

On the other hand, what happens when we don’t eat enough carbohydrates? Well, our body can create its own glucose out of amino acids. And it does this by breaking down muscle, which provides amino acids for the liver to convert to glucose via a process called gluconeogenesis. Now, we can also use fat for energy, but only a small component of fats (glycerol) can be converted into glucose. So, if you’re not eating adequate carbohydrates and are doing any form of anaerobic exercise or strength training, you could be compromising your lean muscle mass! The physiology behind this is too complex for the sake of this post, but keep in mind that the ketogenic diet is often too restrictive for athletes. But, the body will preferentially use glucose as an energy substrate, especially during exercise. And this is a good thing, because it’s protein-sparing  and we want to use protein for functions other than energy creation(come back in 2 weeks for a discussion on protein and it’s role!)

So how many carbohydrates do we need? Well, this depends upon your activity level, your lean muscle mass and your goals! But, it’s safe to say that people need 50-100g of carbohydrates per day, AT MINIMUM. If you’re doing high-intensity, non-endurance exercise you likely need far more than this!  Working with a nutritionist can help you determine your specific needs.

I also want to address the fact that people can develop intolerances to some carbohydrates. The most common of these is lactose intolerance, which is caused by a deficiency of the enzyme lactase. Therefore, lactose will remain undigested and will move to the colon, where it is fermented and results in gas, bloating, abdominal pain and diarrhea. Lactase is active in infants, but declines after weaning. Some studies suggest that only 35% of adults retain activity of lactase, while the remaining 65% of adults have lactase deficiency. Other research has shown that there is improved persistence of lactase persistence in those living in Norhtern Europe, while lactase deficiency is common in East Asia. So, if you experience bloating or gas with dairy consumption, you may have lactase deficiency. But, most people do well with supplemental lactase enzymes (e.g. lactaid).  Keep in mind that Fermentation breaks down lactose in milk; therefore, hard, aged cheeses are often lactose-free.

Others experience FODMAP intolerances. FODMAPS are Fermentable Oligo, Di, and Monosaccharides and Polyols (note: polyols are sugar alcohols), and occur in some foods that are often perceived as “healthy,” including garlic, onions, mushrooms and avocadoes. Essentially, when someone lacks the enzymes to breakdown these carbohydrates, they will travel to the colon undigested, where they will be fermented by the gut bacteria. This leads to bloating, gas and abdominal discomfort. Similarly, folks with SIBO (small intestine bacterial overgrowth) often experience negative symptoms when eating starch, because their bacteria will break down starches before their enzymes can.

Finally, I’d like to remind you that not all carbs are created equal. Many of you likely know that simple carbs are more quickly digested (as we discussed above). The glycemic index is an indicator of how quickly glucose is absorbed into the blood. So, consumption of higher glycemic-index carbohydrates will lead to higher levels of blood sugar more quickly. Similarly, the insulin index is a similar measure, which measures insulin levels after certain foods are consumed. If the goal is blood sugar regulation, we want to do our part to make sure that we don’t get big peaks and troughs when it comes to our blood sugar levels, so limiting consumption of these foods is key.

And what about refined grains? It’s first helpful to understand whole grains.  Whole grains have 3 main parts: bran, germ and endosperm. The bran contains fiber, vitamins and minerals; while the germ contains vitamins and fatty acids. When a grain is refined, the bran and germ are removed, leaving behind the endosperm, which is essentially just starch. Therefore, refined grains are typically devoid of nutrients and are only starch.

Whew, that was a lot of science. I hope you stayed with me. And if not, here are my big takeaways when it comes to carbs:

  • Eat at least 50-100g carbs/day, if not more if you are lifting weights or doing any sort of anaerobic training. We are more sensitive to insulin in the hour following these types of workouts, so be sure to re-fuel with at least 30g of carbs after these types of workouts.
  • Remember that your body can store a LOT of carbohydrates in the muscle and liver, so you don’t necessarily need to be eating carbs before every workout. This is particularly true if you’re someone that exercises first thing in the morning. If you ate carbohydrates the day before, you likely have adequate glycogen stores to get you through your workout!
  • Limit your consumption of high insulin-index foods and high glycemic-index foods, but keep in mind that you can regulate your blood sugar by eating adequate fiber, fat and protein with every meal. This will help to ensure that glucose enters your blood gradually. Also, avoidance of refined carbohydrates is typically wise, as they are often devoid of nutrients (if the packaging says otherwise, it’s often because they’ve been fortified in their processing, so those nutrients aren’t naturally-occurring).
  • Carbohydrates are NOT the enemy. Your body needs them!

Come back in the following weeks for a discussion on the other two macronutrients – fat and protein!

Have questions? Leave them below or shoot me an email, because I’d love to hear from you!

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