Glycemic Index: The Importance Of The Glycemic Index In A Bodybuilding Diet

The Glycemic Index (or GI for short) is a measure of how quickly your blood sugar rises after ingesting a carbohydrate. Basically, once you consume a carbohydrate and it gets digested it gets turned to glucose (blood sugar). Blood sugar is used by the body to manufacture ATP (Adenosine Tri-Phosphate), which is the molecule that the body uses to power up all of its functions. You can think of ATP as your body’s fuel, as without ATP, your organism would not be able to function.

The way that GI works is that each food is assigned a value, typically from 0-100, based on how fast blood sugar increases in the next two hours after consuming a carbohydrate. A value of 100 would represent a food that increases blood sugar very rapidly, such as a straight glucose drink. A value of 59, like the one from brown rice, means that the blood sugar response is way more moderate. Therefore, for the purposes of blood sugar control and fat loss, brown rice is a much better choice than a glucose drink. Now, why is that?

How quickly a carbohydrate is turned into glucose and released in the bloodstream affects the amount of insulin that the pancreas will release to control blood sugar levels. Too quickly of a conversion and your insulin levels skyrocket, a bad situation if you are trying to lose body fat since fat loss cannot occur in the presence of high insulin levels. Such a hormonal environment triggers fat storage. Therefore, it stands to reason that if a carbohydrate is released slowly into the blood stream, then less insulin is released and thus fat loss is maximized.

So is controlling GI the main key to losing body fat? Yes and no. Understanding the effect of foods on your blood sugar is important as several studies have shown that eating low GI carbohydrates throughout the day suppresses the person’s appetite and provides more stable energy levels as blood sugar is better controlled (Note: sudden drops in blood sugar make you feel hungry and lethargic). In addition, eating low GI foods allows for more consumption of food without body fat storage and for a leaner you due to body fat loss. However, there are other factors that affect body fat storage not taken into account by the GI as we will discuss on the next page.

What’s a Low GI Food?

While there are many opinions out there on what a low GI food is, typically a food under 55 is considered low, a food under 70 is medium and anything over 70 is high. However, we must understand that what you eat in conjunction with your carbohydrates will affect your GI. Every time you eat a protein with a carbohydrate the total GI of the meal will go down since protein is a very complex molecule and thus slows down the digestion of the carb. Fats also have this effect. Since you will not be eating just a carbohydrate in your bodybuilding nutrition plan, then the raw GI number should only be used as a guideline. Besides, GI does not provide us with the whole answer as to which carbohydrate is best for us in order to lose fat.

What GI Does Not Take Into Account

An important reason why we cannot take GI as the only measure of whether a carbohydrate that we choose will help us lose fat or not is because GI does not take into account the different ways in which the body handles complex carbohydrates from starches like brown rice (or grains like oatmeal) vs. a simple carbohydrate like an apple. This leads us to the following topic which is Complex Carbohydrates vs. Simple Carbohydrates.

Complex and Simple Carbohydrates

Carbohydrates are divided into two categories: complex carbohydrates and simple ones.

The complex carbohydrates are hundreds of sugar units linked together in single molecules (reason they are called complex) and typically give you more sustained energy (provided they have a medium to low GI) as they take more time to be broken down by the body. Note: Complex carbohydrates with a high GI behave more like a simple sugar, which is digested quickly.

There are two types:

Once again, you should be eating these complex carbs in small portions, but more frequently throughout the day.

  1. Starchy: Provide you with actual raw energy that the body can use. Good sources are Oatmeal, Grits, Brown Rice, Lentils, Sweet Potatoes, and cream of wheat.
  2. Fibrous: The body cannot absorb these but they are rich in vitamins and minerals. In addition, fiber cleans up your intestines, which allows for better absorption of the nutrients that you get from digestible foods. On top of that, mixing fibrous sources with starchy sources lowers the rate of digestion of the starchy carbs thus lowering their GI. Good sources are: Asparagus, Squash, Broccoli, Green Beans, Cabbage, Cauliflower, Celery, Cucumber, Mushrooms, Lettuce, Red or Green Peppers, Tomato, Spinach, and Zucchini.

Simple carbohydrates are made up of one, two, or three units of sugar (at the most) linked together in single molecules, and thus, give you immediate energy as they are released more readily in the body. Good sources are: apples, pears, cantaloupes, oranges, cherries, strawberries, grapefruit, lemon, nectarines, peaches. Higher sugar fruits like grapes or bananas are best for after a workout if desired.

Simple Carbohydrates And Their Effect on Body Fat

Though the glycemic index categorizes most fruits as low GI, as you will see, the simple sugar found in fruits called fructose is metabolized differently than the sugars from starches. To understand how the process differs, first let’s see how the body uses glucose.

If blood glucose levels are low, the body uses the glucose it gets from foods and burns it immediately for energy. This is one of the reasons why after a workout, the body utilizes carbohydrates so efficiently. Now, assuming that there is no immediate need for energy, glucose is then into glycogen and stored in the liver or the muscles. The liver can hold roughly 100 grams of glycogen but the muscles, depending on how muscular you are, may store between 200-400 grams. The key point to remember here however is the following: The glycogen from muscles can only supply energy to the muscles when they are contracting (so muscle glycogen gets depleted badly during a weight training workout). Liver glycogen however can supply energy to the entire body. It is key to remember this in order to understand how fructose does not help with fat loss.

The way that the body gets fat with an excess of carbohydrates is that if all of the glycogen stores in the body are full, then the extra glucose is converted to fat by the liver and stored as adipose tissue (bodyfat), probably in your buns and thighs or around your waist.

Now that you understand how glucose is used and how fat can be stored in situations where all glycogen levels are full, lets go back to the fruits. What happens with fructose is that the muscles do not have the enzyme required to turn fructose into glycogen. The liver does so fructose replenishes the liver. It does not take much to replenish a liver of glycogen as it can hold around 100 grams only. Therefore, if you overdo the fruits, you will fill up your liver glycogen and this causes the body to release an enzyme called phosphofructokinase signaling the body that glycogen stores are full. Since the liver has to supply energy for the whole body, the body uses its glycogen stores as the fuel gauge. When the tank is full, so to speak, that is when any extra fuel gets stored away. Because of this, we suggest that fruits are limited and even eliminated if on an aggressive fat loss diet. By the way, if you are wondering why most fruits can be so low GI and still cause so much damage is because fructose leaves the liver as fat and fat does not raise insulin levels. Bummer!

Carbohydrate Consumption Recommendations

It is recommended that you eat mainly medium to low (55 or less GI) to medium (65 or less GI) glycemic complex carbs throughout the day, as they are responsible for creating consistent energy levels for peak performance and daily functions.

If you must eat fruits, minimize your consumption to two servings per day at times where some of your liver glycogen has been depleted. The best times are the morning with breakfast and right after a workout. This will help to speed up the recuperation time and aid in the production of lean muscle tissue. Ingesting simple carbs throughout the day is not recommended as if your liver glycogen is full, then you will risk storing body fat.



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  1. This is a great article Hugo! The only thing that seems missing is a ‘metabolic’ clarification around why higher GI foods should be avoided…

    In simple terms, because of glucose’s high affinity to react with other molecules, our bodies strictly regulate blood glucose levels to a limited amount of only 5 grams in total.

    Insulin is secreted to manage glucose levels in the blood (insulin also does many other things). More importantly, studies have shown that insulin has 3 effects as it relates to weight management: 1. insulin stimulates lipogenesis. 2. insulin inhibits gluconeogenesis. 3. insulin inhibits autophagy.

    Each of these 3 effects contribute to the chronic deterioration of your body’s metabolic processes.

    I recommend all readers to look each one of them up on Google (or whatever search engine you use) and learn more about them.

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