Nutrition
Every single gram of carbohydrate has 4 calories, equating its energy value to that of protein. While carbohydrates are non-essential (because given the right circumstances, your body can create glucose), when it comes to fueling your body, they are king. Carbohydrates are your body’s first choice of fuel for every activity you do. As discussed in the section on metabolism and energy systems, recall that almost all carbohydrates are broken down into simple glucose (or sugar) molecules. For the 1st 20 or so minutes of all exercise, glucagon stored in the muscle (short term glucose storage) is broken down into glucose and is metabolized as our main source of fuel. The glucagon in muscle is then replenished by glucose in the blood stream. When blood sugar levels drop, the glucagon stored in your liver (long term glucose storage) will be broken down and released into the blood stream to replenish it.
For the majority of the population, the more active a person is and the more muscle tissue a person has, the more carbohydrates they should ideally be eating. Competitive and performance based athletes, should eat the bulk of their carbohydrates around intense and sometimes even during, long duration workouts to ensure they have the energy necessary to perform. This should not be understood that all active people should increase their carbohydrate intake. The vast majority of people in western societies are over-consuming carbohydrates as the norm on a regular basis.
Complex & Simple Carbohydrates
Carbohydrates are either complex, which means they are large and composed of many (anywhere from 10 to thousands) of sugar molecules, or simple, meaning they are small and composed of just one or two sugar molecules. Simple carbohydrates are often sweet tasting, while complex carbohydrates are typically starches and fibers. Most of the whole plant foods we consume will contain a mixture of both complex and simple carbohydrates, while most processed food items contain massive amounts of simple carbohydrates.
The Glycemic Index (GI) & Glycemic Load (GL)
The Glycemic Index (GI) is a system that ranks foods on a scale from 1 to 100 based how quickly the food releases sugar into blood, making blood sugar levels rise. The faster a particular food causes a rise in the blood sugar, the higher the GI score that is assigned. The slower sugar is released into the blood, the lower the GI score that is assigned. Pure glucose is given a score of 100, for example. A GI of 55 or less is considered to be low. A GI between 55 and 69 is generally considered to be medium. Anything over 70 is considered to be high. In general, the more cooked or processed a food is the higher its GI score is, and the more fiber or fat in a food the lower its GI score will be.
GI ratings however, do not take into account typical portion sizes. To understand a food’s complete effect on blood sugar, you need to know both how quickly it allows glucose to enter the bloodstream and how much glucose per serving it can deliver. If a serving of food contains just one gram of glucose that is released into the blood stream instantaneously for example, it will have minimal actual effect on the blood sugar, compared to a serving of food that has 100 grams of sugar that are released over a slightly greater time period.
The Glycemic Load (GL) is a system that combines the data from the GI and the actual carbohydrate content of a typical serving of that food, in order to give a more realistic value of how it may affect blood sugar levels. A GL under 10 is considered low, while 10 to 19 is considered medium, and 19 and above is considered high.
Take watermelon for example. Watermelon contains different types of simple sugars, which individually are released into the blood stream relatively quickly. It typically has a GI score of 72, which seems high. But a 100-gram serving of watermelon, has a considerably low carbohydrate (sugar) content, with just about 8 grams total carbohydrates, combined with what makes up the bulk of the fruit: fiber and water. A serving of watermelon has a minimal effect on blood sugar levels and as such, a GL of somewhere between 2-5, which is really low.
Neither GI nor GL take into account food combining, or what happens to blood sugar levels when you eat foods in combination, for example a potato (higher GI score) with a dollop of butter (slows sugar release) on top. As nutrition coaches, we aim for balance with every meal, and must consider these things even though we may not have exact or accurate numbers to work with.
Many studies suggest that a diet consisting of low GL foods are correlated to lower risk for obesity and chronic diseases, along with higher levels of HDL (which is our good cholesterol).
Fiber
Dietary fibers are carbohydrate food substances containing materials such as cellulose, lignin, and pectin, which are resistant to the action of digestive enzymes. This means our body does not fully digest all of the fiber we eat. While most carbohydrates are broken down into sugars, fiber is only partially broken down while carrying out various other important functions like regulating the use of sugar within our body, before the bulk of it is expelled as waste.
Some Ketogenic and low carbohydrate diets advocate discounting fiber intake because of its resistance to digestion. Because fiber is partially broken down and some calories are still released, we do not recommend this. With our nutrition programming, 1 gram of fiber is considered and counted exactly as 1 gram of carbohydrate.
Fiber can be either soluble, which means it combines with water, or insoluble, which means it does not combine with water. Each type of fiber plays a different, yet important role in your body. When soluble fiber is combined with water it creates a sticky, jelly-like substance. This substance helps slow down the digestion of carbohydrates, which leads to a slower rise in blood sugar. Soluble fiber also helps lower LDL (or bad cholesterol). A few good real food sources of soluble fiber include oats, barley, beans, nuts, apples and blueberries. Insoluble fiber helps bulk up stool volume and speeds up the rate at which food passes through your digestive system, both of which help promote regularity and prevent constipation. Some good real food sources of insoluble fiber include most vegetables, wheat bran and whole grains. Fiber also helps keep us feeling satiated between meals.
The Harvard School of Public Health[1] Offers the following tips for increasing fiber intake:
- Eat whole fruits instead of drinking fruit juices.
- Replace white rice, bread, and pasta with brown rice and whole grain products.
- If you’re going to eat cereal, choose cereals that have a whole grain as their first ingredient.
- Snack on raw vegetables instead of chips, crackers, or chocolate bars.
- Substitute beans or legumes for meat two to three times per week in chili and soups.
Fiber is a fundamental part of any healthy diet. It comes exclusively from plants (fruits, vegetables and grains) and as such, we advocate that all diets be rich in a variety of plant foods. The overall best sources of fiber are fresh fruits and vegetables, whole grains, legumes and nuts.
[1] https://www.hsph.harvard.edu/nutritionsource/carbohydrates/fiber/
