It is hardly a secret that exercise is a fundamental component of living a healthy lifestyle. Along with maintaining a good diet, getting enough sleep, and staying hydrated, exercising regularly can have tremendous benefits for all aspects of physical health and longevity. Whether it’s a brisk jog in the morning, a competitive sport like soccer or football, or lifting heavy weights in the gym, your body will thank you for staying active.

However, as with many things in life, the situation is, unfortunately, a little bit more complex for people with diabetes. For diabetics, exercise can and should still be incorporated as part of a larger diabetes management plan. It may just take a little bit more consideration in order to counter the spike in blood sugar that can sometimes accompany a workout session and leave diabetic athletes confused and frustrated.

To be clear, not all physical activity will cause a spike in blood sugar for all diabetic people. In fact, it can often have the opposite impact. Many diabetics may already be aware that physical exercise can be useful in lowering blood sugar since it increases the body’s energy demands and thereby depletes the circulating glucose levels to meet those demands. But this doesn’t tell the full story, since exercise can have the complete opposite effect of spiking blood sugar during and after a session. In the rest of this article, we will explain which types of exercise are most likely to increase blood sugar, and what you can do to help manage these effects while staying active.

Why does exercise cause blood sugar to sometimes spike?

Your Body’s Perspective

At first, a rise in blood sugar caused by exercise may seem unintuitive. After all, glucose is one of the primary ways the body fuels its various activities, and one would expect that being more active would burn up glucose stores rather than increase them. However, there is a sound physiological explanation for why some forms of exercise actually raise blood glucose levels.

Exercise is very energy intensive, but some forms are more intense and require larger bursts of energy in shorter periods of time. The human body has developed mechanisms to finely control the amounts of glucose circulating in the body in order to meet the current levels of demand based on whatever the body happens to be doing at that time, or what the body predicts it will be doing in the near future. In a perfect situation, the body strikes a precise match and releases the exact amount of glucose required to meet the demands of the moment, leading to a steady or slightly reduced level of blood glucose after exercise. Sometimes, however, the body gets the balance wrong and releases more glucose than is required. When this happens, blood glucose levels elevate temporarily, before typically returning to a baseline.

There are various mechanisms that the body uses to coordinate increases in blood glucose to meet the demands of exercise. Understanding these mechanisms can help better understand how to mitigate their effects. We detail these mechanisms below:


One chemical messenger used by the body is adrenaline, commonly known as the “fight or flight” chemical. Adrenaline, which is a stress hormone, indicates to your body that a stressful event is occurring to which your body should be prepared to react. Part of the adrenaline response is to mobilize energy from your body’s stores in order to navigate whatever stressful situation may be occurring. This is done by inducing the liver to release glucose into the bloodstream, in addition to other physiological responses.

Certain types of exercise are more likely to release adrenaline. These include lifting heavy weights, competing in competitive sporting events, and performing brief, explosive workouts like sprints. This is why these types of exercise are among those more likely to spike your blood sugar.

Man doing deadlift

Lactic acid

Depending on the situation, your body has two modes of energy metabolism that it uses to supply your body with energy during physical activity: aerobic and anaerobic. In aerobic conditions, meaning conditions where your blood has enough oxygen to meet the cellular demands, the glucose in your blood can be converted into energy for your cells to use. Under anaerobic conditions, where you are working so hard that you are unable to keep up with your body’s oxygen requirements, your body undergoes gluconeogenesis; a process that converts lactic acid into glucose for your muscles to use as fuel.

Because gluconeogenesis generates glucose from lactic acid and uses it as a primary fuel source for your muscle cells, your blood glucose is not depleted the way it would be in aerobic conditions. This can cancel out the drop in blood glucose that you might expect to accompany exercise.

For this reason, modes of exercise that put you into an anaerobic state are more likely to cause issues with blood sugar levels than aerobic activities. Planning your exercise activities accordingly can factor into how you manage your blood glucose while being physically active.

Pre-workout food

While not a direct consequence of the exercise itself, one factor which can contribute to increases in blood glucose around workouts is the tendency for people to fill up on carbs ahead of exercise. The rationale for many athletes who do this is that it provides a quick hit of energy that can help fuel their workout and keep them from “crashing” before their workout is over.

Diabetic athletes should be conscious of the fact that exercising will not necessarily counteract blood glucose spikes that result from this practice and should therefore be mindful to apply the same diligence to monitoring their carb intake and insulin intake to pre-workout carbs as they would any other meal.

An alternative to using carbs to power a workout is to instead eat snacks that are high in fats and protein. These can help provide a boost of energy without the spike in blood glucose that might accompany a more typical pre-workout meal.

Pre-workout food

Morning exercise

The timing of your workouts may impact your glucose levels in ways you may not have realized. Generally, exercising first thing in the morning is far more likely to cause a glucose spike than the same workout being done later on in the day. This is especially true if you prefer to hit the gym before you’ve had your first meal of the day.

This is due in part to something called the “dawn effect”. When you wake up, your body naturally increases levels of certain substances in your blood to help you prepare to start your day. Among these is glucose. If you exercise during this period, you will only compound this effect and will likely see an even greater increase in blood glucose.

When you exercise on an empty stomach, your body is forced to release glucose from the liver to compensate for the energy demands placed on it by your activity. This means that you will see a spike in your blood glucose since there is not enough glucose c circulating in your bloodstream that would otherwise have been there from eating a meal.

Morning Exercise

How to counter blood glucose spikes during and after workouts

Ultimately, you may not be willing to give up certain kinds of exercise, nor is it true that you must in order to stay healthy. It is possible to enjoy a wide range of physical activities without compromising your health, as long as you take appropriate measures to respond adequately to the corresponding spikes in blood glucose.

Every person’s situation is unique. Perhaps the best thing you can do is to pay careful attention to how your body responds to different kinds of exercise, at different times of day, having eaten at varying lengths of time prior to exercising. Once you begin to understand and predict how your blood glucose responds in each situation, you can begin to dial in the timing of your insulin intake to best meet your individualized needs. Take care not to overdo it with post-exercise insulin intake; blood glucose spikes may not be desirable, but neither is hypoglycemic episodes caused by being too liberal with your insulin.

One strategy you can investigate is to be strategic about the types of activities you choose to engage in for exercise. As discussed above, short, intense, or anaerobic activities are the most likely to cause a blood glucose spike. Conversely, slow, steady-state, aerobic exercise may have the precise opposite effect by lowering blood sugar levels following a workout. You may consider developing a workout plan that incorporates a balance of these different categories in order to minimize the associated stress on your system.

Consulting with trusted medical professionals should always be an instrumental step in developing a plan to manage exercise-related blood glucose spikes. Be sure you relay all of your observations to your doctor, nutritionist, pharmacist, and anyone else involved in your diabetes treatment management team. One potential approach they may employ is to advise you to temporarily raise your insulin pump’s baseline settings during your workouts. This may pre-empt the necessity for larger post-workout doses of insulin and may substantially reduce the magnitude of any sudden spikes.