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Carbohydrates: A Complex Subject Made Simple

By Marc Perry / July 1, 2017

While there are many hotly debated nutrition topics, few evoke as much passion and interest as carbohydrates (aka carbs). Popular low-carb diets like Zone, Atkins, South Beach, and Paleo limit the intake of carbs, while others like the Ornish diet call for high carbs as the path to optimal health.

Who is right? Are carbs evil? What are carbohydrates anyways?

While carbohydrates can be a very confusing subject, the following will break down all the important concepts, definitions, and topics related to carbohydrates to turn a complex subject into a simple one. Future articles will expand and explore each concept in more detail.

What are Carbohydrates?

Carbohydrates are found in foods including fruits, vegetables, grains, potatoes, pastries, and candy and are considered the bodies preferred energy source. More specifically, carbs are sugar molecules that are a union of carbon, hydrogen, and oxygen (CHO). Think of carbs as one, or more sugar molecules that are bound together and broken down by the body to be used as fuel.

Here’s a quick list of carbohydrates for your reference:

Types of Carbohydrates

Carbohydates are classified in many different ways:

  • healthy vs. unhealthy
  • good vs. bad
  • slow vs. fast
  • simple vs. complex
  • No wonder people get so confused!

    Remember, carbohydrates are just sugar molecules, all of which are broken down by the body into glucose. Glucose is a single sugar molecule that is used as fuel by the cells in your body from your brain to your muscles.

    There are 3 types of carbohydrates that are defined by the number of sugar molecules they contain:

    1) Monosaccharide – one sugar molecule, examples include glucose, galactose (in milk), and fructose (in fruit)

    2) Disaccharide – two sugar molecules, examples include sucrose (table sugar), lactose (in milk), and maltose (in beer).

    3) Polysaccharide – several sugar molecules, examples include starchy foods like pasta, or potatoes, and fiber, which is the indigestible part of a plant that aids in digestion.

    When a carbohydrate is “simple” it refers to mono & disaccharides that are easily absorbed into the bloodstream because of their simple molecular structure. Think milk, fruit, and table sugar. “Complex” carbs on the other hand are polysaccharides and because of their more complex molecular structure can take longer for the body to break down into sugar. Think grains, vegetables, and potatoes.

    You may be thinking, “Ok, so simple carbs are bad and complex carbs are good, right?” The answer is not that simple as you’ll learn in a moment.

    Function of Carbohydrates

    Before digging deeper to understand what carbs to eat, we need to understand how carbohydrates are used and stored in the body.

    As carbohydrates are broken down and enter the bloodstream, they increase the amount of sugar (glucose) in the bloodstream. The level of sugar in the bloodstream is called your blood sugar level. As you eat carbs, your blood sugar level rises, which activates the hormone insulin to suck the excess sugar out of the bloodstream and into your muscles (which can absorb about 300-400 grams) and your liver (which can absorb 100 grams).

    What happens if your sugar storage tanks (muscle & liver) are full and you keep on eating carbs? Any excess glucose that is not used by the body for energy will be stored as fat. The more “insulin sensitive” your muscles are, the more readily they will suck in sugar instead of having that sugar get converted to fat. And what’s a great way to make your muscles more insulin sensitive? Strength training of course!

    Good Vs. Bad Carbohydrates

    Many nutritionists do not use the word “bad” when describing food because as the saying goes, “there are no good, or bad foods, only good, or bad diets”. With that said, carbohydrates that cause your blood sugar level to rise rapidly are generally considered bad, or unhealthy carbs whereas those that are absorbed slowly and have little effect on blood sugar levels are considered good, or healthy carbs.

    The Glycemic Index was created to measure the speed with which carbohydrates are converted to glucose. Foods that digest quickly are high on the index, which ranges from 0 to 100, and foods that digest slowly are lower on the index. This is important because large spikes in insulin levels affect your hunger (can make you even more hungry), can negatively impact fat loss, and even lead to diabetes if levels are chronically elevated from over consumption of fast digesting carbohydrates.

    Here’s a short list of some high and low glycemic carbohydrate foods:

    While the Glycemic Index can be helpful, it’s not perfect. For example, some ice cream can show up as 30 on the glycemic index, along with some other carbohydrate sources like spaghetti that are nutritionally anemic and provide substantial calories in small servings. In addition, foods like watermelon that are high on the Glycemic Index impact blood sugar levels far less when adjusted on a per serving basis (watermelon is mostly water, hence the name). This concept is referred to as the Glycemic Load. Lastly, when combining the carbohydrates with different foods like dietary fat, the pace of digestion can slow down.

    Confused? Don’t be. If you are eating whole, natural, unprocessed carbohydrates, you can consider them a good carb, but if the carb was made in a lab, or has been processed such as soda, candy, or white bread, it’s a “bad” carb, or better yet – not ideal. I don’t like using the bad word unless describing High Fructose Corn Syrup, which is a chemically altered sugar found in tons of foods we eat every day. More on HFCS another time!

    Do Bad Carbs Make You Fat?

    I wish I could answer this question easily, but even an experienced researcher with a PHD would cringe at the thought of a proper answer.

    There are two primary camps that attempt to describe how we gain and lose fat:

    1) Energy Balance Theory – If you eat more calories than you burn, and you gain weight and if you eat less calories than you burn, you lose weight. This theory is based on the law of thermodynamics where energy can neither be created nor destroyed. You can eat as many carbs as you like and as long as you eat less total calories than you burn, you will lose weight. Harvard Medical School, The Institute of Medicine, along with most large and reputable organizations support this theory.

    2) Carbohydrate Hypothesis – Carbs, not calories make you fat is the summation of the carbohydrate hypothesis. Proponents include Dr. Robert Atkins, Dr. Michael Eades, and other medical and nutrition experts who view carbs as the root cause of the obesity epidemic. As long as you sufficiently decrease your carb intake, you will lose weight.

    Who’s right? Well that’s worthy of a separate blog post for sure, maybe even a book, but my best guess is the truth lies somewhere in the middle; eating less calories helps you lose weight, but eating too many carbs and not enough protein may have you gaining fat, and possibly even losing muscle. Furthermore, genetics, hormones, and activity level play a huge role in how easily carbs are stored, used as energy, or converted into fat.

    Eating some candy, or cookies here and there will not make you fat, but eating a lot of fast digesting carbs combined with excess calories and no exercise is a great strategy for adding a bunch of body fat.

    So How Many Carbs Should You Eat?

    This question will also be explored in more detail in a separate post, but here’s the short scoop:

    The amount of carbohydrates you should eat depends primarily on your genetics, body size, and activity level. If you are a 180lb sedentary guy who wants to maintain weight with a few workouts per week, a good benchmark for carb intake is around 200 grams of carbs. The more active you are, the more carbs you can add. Endurance athletes can and should eat around 300-400 grams per day to help fuel their workouts. The minimum RDA (Recommended Dietary Allowance) for carbs is 130 grams, with 55% of total calories coming from carbs as the general recommendation.

    From an evolutionary standpoint, carbohydrates are not essential, which means we do not need to consume carbs in order to function. In fact, if you eat no carbs at all, your body will break down body fat into small molecules called ketones. Ketosis is this process of creating ketones when our body uses primarily fat for energy, which is associated with a carb intake of under 25 grams (under 100 grams is when ketones are first present in the bloodstream and urine). Our bodies not only use fat for energy during ketosis, but may also convert protein (both dietary and muscle) into carbs to be used as fuel.

    You may be thinking – “I need to get into a state of ketosis immediately” given the apparent fat burning potential. While ketosis is a cool adaptation, it may leave you with low energy levels, really bad breath, inability to concentrate as effectively, along with serious vitamin and mineral deficiencies. Furthermore, research studies do not show fat loss is any greater during ketosis versus a diet of equal calories with a lot more carbs.

    When it comes to carbs, use your common sense – a few servings of fruit, plenty of veggies (which provide few calories but tons of nutrients), some starch/grains (or a lot if you are very active) each day should help fuel your body and provide the essential nutrients it needs to function optimally.

    Reference of Carbohydrate Terms

    Carbohydrate – sugar molecules that are a union of carbon, hydrogen, and oxygen (CHO) and are broken down by the body to be used as fuel. One sugar molecule is a monosaccharide, two is a disaccharide, and more than 10 is a polysaccharide.

    Glucose – A monosaccharide found in plant and animal tissues, which is transported by the blood to all the cells of the body to be used for energy.

    Glycogen – A polysaccharide that is the main form of carbohydrate storage in animals and occurs mainly in liver and muscle tissue; it is readily converted to glucose and glucose is converted into glycogen.

    Glycemic Index – an index ranging from 0 to 100 indicating the effects of various foods on blood sugar. Fast-releasing foods that raise blood sugar levels quickly are high on the index, while slow-releasing foods, at the bottom of the index, give a slow but sustained release of sugar

    Gylcemic Load – an index indicating the amount of carbohydrate contained in a specified serving of a particular food. It is calculated by multiplying the food’s glycemic index by its carbohydrate content in grams and then dividing by 100.

    Blood Sugar Level – The concentration of glucose in the blood, measured in milligrams of glucose per 100 milliliters of blood. The normal fasting value is between 3.9 and 5.6 mmol/l.

    Ketosis – the abnormal accumulation of ketones in the body as a result of excessive breakdown of fats caused by a deficiency, or inadequate use of carbohydrates

    Insulin – A hormone secreted by the pancreas in response to high blood sugar levels. Insulin regulates the body’s use of glucose and the levels of glucose in the blood by acting to open the cells so that they can intake glucose

    Glucagon – a hormone secreted by the pancreas that acts in opposition to insulin (raises concentration of sugar) in the regulation of blood glucose levels.

    Fiber – a type of carbohydrate that is coarse, indigestible plant matter that when eaten can help improve digestion.


    • anthony says:

      I forgot to mention im 24 :)

    • anthony says:

      So should that be my normal weight? Or training weight? Am I currently underweight then?

      I have calipers that seem to indicate my bf is very low even sedentary.. (Thigh and abdomen come up as 10%, chest is about 5).. Is their a good chance I am suffering from something? Youd think id be in the 20% range if im inactive.. How many calories should I be getting a day regardless of activity? If I have to eat extra calories just to be at anormal weight is something wrong with me? (hope that makes sense)
      its just im a bit worried, as people tell me I look ill,..

    • Marc Perry, CSCS, CPT says:

      @anthony - it sounds like you should schedule an appointment with your doctor would make sense.

    • anthony says:

      Its just my doctor tells me my weight is fine, yet many people disagree.
      im an ectomorph, but having said that, my normal sedentary weight used to be about 150.
      is their any chance you could possibly just tell me how to correctly use the calipers, as im finding contrary information. I dont even know how much skin to take into the fold.

      also what is your weight roughly? Just as a rough guide for me to aim for..

      • Marc Perry, CSCS, CPT says:

        @anthony - My weight is 170lb and I'm 5'11" and my body fat is around 7%. I would suggest going to the manufacturer of the calipers and getting a manual from them, but I do agree with you I should have a post on how to measure your body fat with skin fold calipers. The idea is you want to make the space between your index finger and thumb and inch wide, pull the skin and fat clearly off the muscle, then measure the space about a centimeter from your thumb.

    • Stacy says:

      Quick question on nutrition….

      My stats: 135lbs, 5’6
      My daily macros: 1360 cals / 135 protein / 100 carbs / 45 fat
      Exercises 4 to 5 times a week: includes cardio, and strength training for muscle building…all exercise at a moderately high to high intensity each workout.

      I stay really close to the my macros each day. I am not sure if 100 carbs is enough, though...especially after reading about ketosis in this article. I only eat the bulk of my carbs breakfast and post-workout. I have noticed that I do not retain as much water…which is a plus, but no weight loss at all after 4 weeks of this carb decrease and timing change.

      In your opinion, do I need more calories? Also, do I need more carbs? I read in some articles that 100g of carbs is needed just to maintain body functions, so maybe I am defeating my efforts by not eating enough carbs to supply my workouts. Not sure. My goals are to build lean muscle, decrease fat and overall be healthy.

      Any advice is appreciated.

      Thanks for you advice.

      P.S. I sent this in an email previously, but thought I would post here instead.

      • Marc Perry, CSCS, CPT says:

        @Stacy - I apologize for the delay in my response. Typically under 50 grams is when ketosis really kicks in, so in my mind 100 grams is likely fine. If you were a 180lb man, I would say it may be a little low. Generally speaking, I actually recommend taking calories even lower, rather than increasing. In my Weight Loss Plateau: Tips on How to Break It article, I talked about the calorie creep. While this may not be happening to you, a 1200 calorie diet I've found to be the sweet spot for many women. I've also found people in general vastly overestimate calorie burn, not that you are. The reality is that losing fat especially as you get leaner is not extremely pleasant. I would definitely read that article closely and see if it helps.

    • Stacy says:

      Thanks Marc. I will check out the article you mentioned.

      Have a great day!

    • Donald says:


      first off congratulations on the best fitness website in the world I think you have probably helped thousands of people with their health which is the most important thing a person could have. on behalf of the human race I would like to say well done.

      One thing im confused with is the subject of fruit obviously you should eat it but at the beginning of your article you said that because fruits have simple Monosaccharide sugars they quickly enter the bloodstream which is a bad thing. however they are low on the glycemic index which would suggest the opposite. could you clear this up please?

      • Marc Perry, CSCS, CPT says:

        @Donald - Thanks, Donald for your very nice comment! Fruits are absolutely ok to eat in moderation and some are higher on the glycemic index than others. In fact, a grapefruit for example is only a 25 on the glycemic index. My favorite type of fruits for fat loss is watery fruits like grapefruit, orange, and an apple, or berries like strawberries, and blueberries.

    • Matthew Zastrow says:

      This is a great summary! Thanks for posting this material!

    • Mike says:

      One correction. Ketosis does NOT make you miserable or foggy or give you bad breath (at least not for more than 2-3 days).

      I have lost 18 lbs in 4 months and can lose 3-4 lbs a week as desired while performing better cognitively (the brain prefers ketones over glucose) and eating...wait for it...pepperoni, butter, sausage, hamburgers (no bun, please), cheese and BACON. No fad, no scam, just the science of the human body.

      Our bodies prefer ketones to glucose and in the absence of carbs and just moderate protein (and very high levels of healthy fats - no trans fats but lots of olive oil, MCT oil, fatty fish, beef, etc.), we will burn fat incredibly efficiently because our body fat will break down into ketones to be our source of fuel.

      I was skeptical at first because of the low fat rhetoric that has gone on for so long, but I spend 6 days a week eating high fat and keep having to downsize my jeans. Just sayin.

    • Marc Perry, CSCS, CPT says:

      Hey Mike, thanks for sharing your insights into following a keto diet. I've tried it myself with lackluster results, but the cool thing is we all respond differently and I'm pumped that it's worked well for you. I'm going to keep the wording of my article because I say "may" cause certain issues, which it does for some. But I did take away the sentence "Why be miserable...". Again, very happy to hear you have found keto has worked very well for you. Regarding the fatty meats, that's your own call the types of animals / meats you eat, I think some of the low carb / keto advice is misguided around eating fatty meats like bacon, but that's just my opinion