top of page

Carbohydrates: Everything You Need To Know!

Carbohydrate is one of the energy substrates, meaning that it is a component of food from which we can derive the energy needed to support body functions.

Carbohydrates have multiple functions that are critical to both human health and athletic performance. The basic functions include the following:

(1) providing a source of energy for cellular function,

(2) energy storage as glycogen,

(3) sparing protein,

(4) breaking down fats for energy,

(5) normal GI function,

(6) being a part of other compounds, and

(7) converting carbohydrates to fat. Importantly, carbohydrate in the blood (blood glucose) is the primary source of energy for the brain

Carbohydrates include sugar, pasta, and bread. All carbohydrates are made of one of three monosaccharides. All three molecules contain Carbon, Hydrogen, and Oxygen. Their various forms give each sugar its own qualities, such as taste.

Glucose is the principal source of energy for cells and is a moderately sweet sugar derived primarily from fruits and vegetables. Because of its important function in cellular energy metabolism, sustaining blood glucose level is an important strategy for sustaining athletic performance.

Fructose - Like Glucose, but with a different form. That means it behaves differently with your body. The sweetest of the three simple sugars is fructose. It enters the bloodstream but has no effect on blood sugar levels.

Only Glucose impacts blood sugar. Upon absorption, fructose is transported to the liver to be broken down into 6 Carbons, 12 Hydrogen, and 6 Oxygen molecules. The former fructose molecule is then released into the bloodstream. It now has a glucose effect on blood sugar and can be stored as glycogen in muscle cells.

There are many more simple sugar combinations. Oligosaccharides are anything larger than a disaccharide but less than 6 monosaccharides. These are maltodextrins, and are just somewhat sweet.

These are starches. Starches are lengthy strands of sugar molecules strung together like pearls. In plants, starch is Glycogen. It's not sweet at all.


The indigestible polysaccharides are commonly referred to as fiber or dietary fiber and, while they cannot be digested to provide energy, are important for sustaining the health of the GI tract.

Different types of dietary fiber, including soluble and insoluble fiber, have different physiological effects. Foods containing soluble fiber (gums, mucilages, and pectins) include fruits, oats, legumes, and barley, and have the effect of decreasing gastric emptying time (i.e., reduce the amount of time foods are in the stomach), but also decrease the rate at which glucose is absorbed in the small intestine.

This is an important health benefit, since lowering the rate of glucose absorption also lowers the insulin response, which would help to sustain normal blood sugar longer and may also lower the rate of fat manufacture by cells.

Important Factors to Consider

  1. Carbohydrates have many functions that are necessary components of good health and athletic performance. Consumption of more protein and/or fat is not a replacement for carbohydrate, and these other energy substrates cannot adequately fulfill carbohydrate functions.

  2. Low-carbohydrate intakes cause proteins to be broken down to create needed carbohydrate in the liver (gluconeogenesis), but because humans have no storage of protein, this process causes a loss of muscle mass from which the protein is derived. The protein-sparing effect of carbohydrates, therefore, is an important part of why carbohydrates are needed.

Carbohydrate Digestion

The purpose of digestion is to break down consumed carbohydrates into a form that allows them to be transferred through the intestinal wall and into the blood, where they can be distributed to cells. Digestion of carbohydrate takes place in the mouth and small intestine and involves conversion of more complex carbohydrates (starch and glycogen) to less complex carbohydrates (disaccharides) and then to single-molecule sugars (monosaccharides) to be absorbed.

The Glycemic Index

The glycemic index compares the potential of foods containing the same amount of carbohydrate to raise blood glucose. However, the amount of carbohydrate consumed also affects blood glucose and, therefore, the insulin response. The glycemic load is calculated by multiplying the glycemic index by the amount of carbohydrate (g) provided by a food and dividing the total by 100.

Each unit of glycemic load represents the equivalent blood glucose-raising effect of 1 g of pure glucose.

The dietary glycemic load equals the sum of the glycemic loads for all the foods consumed in the diet and may be used to describe the relative quality of the diet. In general, it is good to be consuming foods with a relatively low glycemic load:

Carbohydrates & Human Performance

In virtually all types of physical activity, carbohydrate availability is considered to be the limiting energy substrate in performance. That is, when carbohydrate runs out, the ability to perform physical activity at a high pace is limited, and performance drops. The human system has limited storage of carbohydrate relative to the other energy substrates, fat and protein, and the availability of carbohydrate is worse than it seems. Exercise typically accesses specific muscles that use muscle glycogen at a faster rate than muscles that are not used, and these muscles can deplete muscle glycogen relatively quickly.

One to two hours before an activity, low GI diets have been shown to increase endurance. Cycling performance was evaluated after consuming the same amount of carbs, either lentils (low GI) or potatoes (high GI) (a high GI food). The lentil group cycled at the same intensity for 20 minutes longer than the potato group. Other research has verified these findings.

It's possible you're wondering how this relates to my workout. It does and does not. Low GI foods are only beneficial for workouts lasting 90 minutes or more. Using low GI foods will benefit anyone who spends more than 90 minutes in the gym or who participates in activities like swimming, soccer, marathons, or triathlons.

Why Low Carb Diets Are Risky

The body will use muscle and fat as energy if it is denied carbs. When you are conducting high intensity activity lasting fewer than 2-3 minutes, your body will go to muscle tissue for energy.

Lower intensity activity, like strolling, uses mostly fat as fuel, but instead of using carbohydrates, your body is uses muscle tissue as a backup fuel source. That means a lot of muscular tissue is broken down for energy. More significantly, low carb diets replace lost carbohydrate calories with fat and protein.This increased fat intake can raise cholesterol and LDL (low density lipoprotein) levels. Overall, this leads to muscle loss and increased cardiovascular disease risk.


Physically active people should consider that only the energy substrates (carbohydrate, protein, and fat) provide the carbon chains needed to produce ATP.

Physical activity elevates the rate at which blood glucose is utilized and can result in low blood glucose, which is associated with premature mental muscular fatigue. Different carbohydrates are best consumed at different times.

When not exercising (pre- and post-exercise), starch-based complex carbohydrates are best for ensuring optimal glycogen storage. During and immediately after exercise, a combination of sugars is best to sustain blood glucose to provide energy to working muscles and for replenishing glycogen stores.



My name is Steven Goldstein

With over 10 years of experience in the fitness industry, I have worked with clients of all ages and fitness levels. From professional athletes to individuals aiming to lose weight, I have helped countless people achieve their goals and improve their overall health through customized training and nutrition plans.

Untitled design(18).png

Consistency leaves clues

Hundreds of clients of all ages, backgrounds, and abilities have put their health in our hands over the years and achieved truly remarkable results. 

bottom of page