Exercise and Insulin Resistance: Why Carbs During Exercise Don’t Spike Insulin

Athletes are constantly searching for clarity around carbohydrates, blood sugar, and insulin, especially as conversations around exercise and insulin resistance become more common. At Hummingbird Fuels, we focus on cutting through confusion with evidence based explanations that reflect how the body actually works during training.

In our Fuel Science Corner, we sit down with food scientist Richard to explain how insulin sensitivity and exercise are connected, and why carbohydrate intake during workouts does not affect the body the same way it does at rest. Understanding the relationship between exercise and insulin sensitivity is essential for endurance athletes who want to fuel confidently, support performance, and protect long term metabolic health.

Exercise and Insulin Sensitivity: How Your Body Uses Carbs at Rest vs During Exercise

Your body handles carbohydrates differently depending on whether you are resting or active. This difference is central to understanding exercise and insulin resistance.

At Rest: Insulin Response and Energy Storage

When you eat carbohydrates while inactive, sugar enters your bloodstream. Your pancreas releases insulin, which moves glucose out of the blood and into storage in your liver and muscles. This is the insulin response most people are familiar with.

Richard explains,
“When you’re inactive and you have carbs, your pancreas releases insulin. That insulin clears the sugar from the blood and sends it to the liver for storage.”

At rest, your body prioritizes storing energy for later use rather than fueling immediate movement.

During Exercise: Improved Insulin Sensitivity and Muscle Fueling

Once you start exercising, your muscles become the primary drivers of blood sugar uptake. During exercise glucose transporters in muscle cells migrate from the center of the cells , allowing sugar to move directly from the bloodstream into working muscles with minimal reliance on insulin.

Richard adds,
“Your muscles start calling out for sources of energy. They start taking sugar directly into the muscle almost independent of insulin.”

This is why carbohydrates consumed during exercise support performance instead of being stored. It also explains why carbs during workouts do not cause the same insulin release seen at rest and actually improve exercise and insulin sensitivity.

Why Exercise and Insulin Sensitivity Matter for Athletes

Understanding how insulin works during movement is especially important for athletes managing exercise and insulin resistance or trying to improve metabolic health.

When you consume carbohydrates during exercise, they:

• Go directly to working muscles for immediate energy

• Help delay fatigue and maintain power output

• Do not cause large insulin spikes like eating at rest

Richard summarizes it simply,
“That’s why you can have carbohydrates during exercise. It doesn’t trigger a massive insulin response. It actually helps you move.”

This is why carbohydrate fueling is a cornerstone of endurance performance.

Related blog post: Carbs for a Race: How Many You Really Need (Before, During & After)

Practical Fueling Tips to Support Insulin Sensitivity and Exercise

Even though insulin plays a smaller role during activity, timing and carbohydrate type still matter.

For shorter sessions under 60 minutes, water may be enough. Some athletes benefit from a small amount of quick carbohydrates such as fruit or a high carb drink mix from Hummingbird Fuels.

For workouts lasting longer than 60 minutes, incorporating easily digestible carbohydrates like drink mixes, gels, or small snacks during exercise bouts helps maintain energy and focus.

Hydration also plays a critical role. Fluids support muscle function and help your body efficiently use glucose during exercise.

These strategies support endurance performance while reinforcing positive adaptations related to exercise and insulin sensitivity.

Exercise and Insulin Resistance: Long Term Health Benefits

Beyond performance, regular training combined with proper fueling can improve how your body responds to insulin. Aerobic and resistance exercise both increase insulin sensitivity over time, helping reduce insulin resistance.

Richard explains,
“The fact that you require fuel for intervals and training is baseline. How you do it is personalized, but carbs are essential for supporting energy without negatively impacting blood sugar.”

Strategic fueling allows you to train harder, recover better, and support long term metabolic health.

The Takeaway on Exercise and Insulin Sensitivity

Carbohydrates consumed during exercise behave differently than carbs eaten at rest. During activity, your muscles pull glucose from the bloodstream with minimal insulin involvement. This makes carb fueling during workouts both safe and effective.

Understanding the science of exercise and insulin sensitivity allows you to fuel confidently, maintain consistent energy, and support long term health.

For guidance on pre workout fueling, read our blog on what to eat before a bike ride. For simple, science-backed fuel during training and racing, Hummingbird Fuels offers a high carb drink mix for cyclists and everyday athletes that is easy to digest and built for performance.