ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, Glycemic Index: What Is It & How Does It Affect Your Fitness

Glycemic Index: What Is It & How Does It Affect Your Fitness

Reading Time: 6 minutes 9 seconds


Date: 2021-01-20T00:00:00-05:00

Whether you are a fitness professional or average gym-goer, you've likely heard that achieving results comes down to two things:

  • 80% diet

  • 20% exercise

While each person is different, the role that macronutrients play in a client's exercise abilities is crucial. They are used in large amounts for both performance and recovery. One of the most important nutritional components that influences exercise is the glycemic index of foods. Let's break down the essential of how this impacts your clients.

When discussing nutrition with clients, be sure to understand your scope of practice and refer out to other professionals, such as your client's medical doctor or dietician, as needed. Want to lean more about nutrition? Check out the ISSA's Nutritionist course to learn more about why clients eat the way they do and how to help them achieve a healthier lifestyle change.

What is the Glycemic Index?

The glycemic index (GI) indicates the effect carbohydrates have on blood sugar. Foods are represented by a number or category, which determines how much they increase blood glucose levels. The glycemic values can range from 1 to 70 with 1 being low and 70 being high.

They are split into the following categories:

  • Low glycemic index foods have a value anywhere from 1 to 55.

  • Medium glycemic index foods have a value anywhere from 56 to 69.

  • High glycemic index foods have a value of 70 and up.

Foods that have a lower glycemic index digest much slower. Whereas high glycemic index foods digest extremely fast. This is what causes large spikes in blood sugar.

A client's blood glucose levels in the body increase mainly from high glycemic food. Low glycemic food has much less of an effect on blood glucose because the absorption rate is much slower. This is important to know because during exercise the body uses stored sugar first.

This sugar is normally stored in the muscles and liver. But when the body depletes is stores of muscle glycogen and energy in the liver, it begins to use energy from the blood. The more intense the workout, the more blood sugar the body uses.

Blood Sugar Levels and Exercise

Maintaining and regulating blood sugar levels are important aspects of good health. This helps reduce the risk of diabetes and other dangerous diseases. Understanding how the glycemic index influences blood sugar levels is important to preventing disease.

It is important to know that:

  • A blood sugar level of less than 140mg/dL is considered to be normal.

  • A blood sugar level of between 140 and 199 mg/dL shows signs of pre-diabetes.

  • And anything above 200 mg/dL is considered diabetes.

The goal is to avoid a buildup of excessive amounts of sugar in the blood. Exercise can help lower blood sugar levels by increasing insulin sensitivity. Insulin sensitivity allows the body to use more glucose in the blood for energy. As blood sugar levels rise, the pancreas secretes this hormone called insulin. This hormone triggers cells to absorb sugar in the blood.

Remember that when there is an excess amount of glucose in the blood, insulin resistance can occur. This reduces a client's ability to absorb sugar and leads to diabetes.

Moderate exercise has the greatest effect on lowering blood sugar. Any form of exercise that is more intense, such as a sprint, will force the body to use stored energy in the muscle and liver.

Even though some forms of HIIT can improve blood glucose. Still focus on long-duration or endurance exercise to lower sugar levels. This type of exercise paired with a low glycemic diet produces the best results.

 ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, Glycemic Index: What Is It & How Does It Affect Your Fitness, Fruits, Vegetables

Benefits of Low Glycemic Foods

Low glycemic foods are an effective option to help clients manage weight and increase satiety. Because they take much longer to digest it helps control appetite levels. The best time to consume low glycemic foods is prior to a workout. This helps the body sustain energy levels for a longer period of time.

Foods like beans, peas, fruit, and vegetables have a low glycemic index (low GI or LGI). Avoiding high spikes in blood sugar through consuming these foods helps prevent the body from losing its ability to lower blood sugar when needed. The constant spike and decline in levels is what leads to type 2 diabetes. It gets to a point where the body is unable to control blood sugar on its own.

Though it doesn't matter if your client has diabetes or not. Everyone should be counting sugar. Low glycemic foods tend to contain more fat and therefore metabolize much slower.

It is important to encourage all clients to consume a diet consisting of low GI foods. Additional benefits of these foods are improved cholesterol and blood pressure, weight loss, and lower risk of heart disease and cancer. Nutrients like fiber, potassium, vitamin c, iron, and antioxidants are found in conjunction with low GI foods.

Additional low glycemic foods to include in one's diet are,

  • Fruits

  • Vegetables

  • Nuts

  • Low fat milk

  • Bran cereals

Combining low glycemic index foods to make a LGI meal before a workout will optimize a client's fitness.

Benefits of High Glycemic Foods

Opposite of low GI foods, high glycemic index (high GI or HGI) foods provide a quick source of energy. The digestion and absorption rate are much quicker in high GI foods. Therefore, they do not provide long-lasting energy. High GI foods can sustain short bursts of high intensity exercise, but not much more than that.

High GI carbs can be dangerous to the health of clients if consumed in large amounts and too often. The rapid spike in blood glucose levels that high GI foods cause can lead to serious damage. Consider consuming carbohydrate-rich foods that have a high GI mainly after a workout.

After a workout, the body is depleted of sugar and energy stores. This increases the need for sugar in the body. The muscles are actually wanting to replenish the sugar that has been lost. In this case, high GI carbs consumed after a workout will be used more efficiently. Consuming a HGI meal after a workout won't have such a negative effect on the body.

They are quick-absorbing and satisfy the body's need for carbs and energy. This leads to better muscle recovery and repair. And fewer spikes in blood sugar.

High GI food usually consists of sugary foods but also include,

  • Whole wheat bread

  • Potatoes

  • Oatmeal

  • Bagels

  • Watermelon

  • Rice

Glycemic Load

The glycemic index is a great measure of how carbohydrate-rich foods will influence a person's blood sugar. But each person is different when it comes to how much they can eat without it having a major effect. The amount of food a person eats and how it influences blood glucose is determined by the glycemic load. The glycemic load (GL) of food is a value that estimates how much food raises a client's blood glucose.

Every client has a different carb tolerance. This is one of the reasons that some clients may not be experiencing results to the extent they want. By knowing how their body reacts to carbohydrate-rich foods they can make adjustments in their diet to improve their progress.

The biggest difference between the glycemic index and glycemic load is the portion size. Aim to keep the glycemic load for clients under 100 each day. The amount in which blood glucose levels rise and fall throughout the day depends on both the glycemic index and load.

Identifying Glycemic Load

Low GL foods normally hold a value of less than 10. Some low glycemic load foods include:

  • Fruits, like apples and oranges

  • Kidney beans and lentils

  • Nuts

Medium GL foods range from 11-19. Some medium glycemic load foods include:

  • Rice

  • Oatmeal

  • Whole grain bread

  • Whole grain pasta

High GL foods hold a value of 20 and up. Some high glycemic load foods include:

  • Baked potatoes

  • Processed cereal

  • Candy

  • White flour pasta and bread

Consider both GI and GL values to help your clients achieve better results and sustain them long term. Remember that simple sugars are digested a lot quicker than complex carbohydrate food. You will not be able to predict how blood sugar levels are affected by just labeling them simple or complex.

Don't just assume that simple sugars have a high GI and complex have a low GI. It is not always an indicator of how they influence sugar levels.

Other factors play a role as well. The more ripe or processed foods are, the higher the glycemic index. If foods contain more fiber and fat, then they will have a lower glycemic index. These factors influence the speed of digestion, making them either low or high GI foods.

Looking to expand your nutrition knowledge and help even more clients? Check out the ISSA's Nutritionist program. Specializing as a nutritionist gives you the ability to offer more services to your clients and help them achieve the best results possible.

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By becoming an ISSA Nutritionist, you'll learn the foundations of how food fuels the body, plus step by step methods for implementing a healthy eating plan into clients' lifestyles.

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