“When is the best time to exercise,” is one of the most common questions I get asked by diabetics and non-diabetics alike. A common belief is that low intensity cardio on an empty stomach burns the most fat because carbohydrates are not available.

First, low intensity cardio is not the best for fat loss. The fat burning zone is myth that does not take into account all the calories burned during and AFTER the exercise session and can actually cause you to lose muscle. If you want to lose fat, then you must preserve your muscles.

Second, research has shown that there is no difference in how much fat is burned during a moderate intensity cardio session with or without food. It does make a difference at lower intensities, but I already said that this is not ideal. At high intensity training, you need some food to maintain performance. So actually by eating a small amount you are allowing yourself to exercise harder and as a result increasing the amount of calories that you will burn hours after your exercise session.

Third, you risk increasing the level of your stress hormones and instead of breaking down fat, your body may break down muscle. Again lowering your metabolism and pushing you in the opposite direction of fat loss.

Exercising on an empty stomach can actually cause your blood sugar to increase if you have diabetes. This seems very strange since most of the time exercise helps to lower blood sugar levels. Exercising tells the liver to release its stored sugar or glycogen into the bloodstream but if there is not enough insulin in the bloodstream the muscles cannot absorb the sugar quickly enough.

People with diabetes must check their blood sugar before and after exercise to determine their response to exercise. If your blood sugar is very high (consult your health care provider for the suggested level) then exercise could make it even higher. This happens due to the stress hormones causing the release of sugar into the bloodstream, often because of limited insulin. If your blood sugar level is high test for ketones in your urine. If there are ketones then you should NOT exercise until your blood sugar is at a safer level.

Research is showing that you may be able to exercise safely with high blood glucose level as long as there are not ketones in the urine. Speak to your health care provider for specific recommendations. In this case, keep the exercise intensity low, because high intensity exercise can raise your blood sugar levels even further.

Now, I know I just said to avoid low intensity exercise for fat loss but under these conditions, preventing your blood sugar from going higher is more important for your health and the prevention of diabetic complications. All exercise helps your diabetes even if it doesn’t promote weight loss. I’d much rather you keep the habit of exercising than skip it because it isn’t the most efficient for fat loss. Remember you are exercising for both your health and fat loss. Your health has priority over fat loss.

Exercise can also cause low blood sugar. As the muscles are working they are absorbing sugar from the blood stream far easier than they do when they are not working. If your blood sugar is too low before you start exercising you must eat some carbohydrates beforehand. This is not ideal for fat loss, so timing your exercise session after you eat and avoiding the peak time of your insulin is best. Depending on the length and intensity of exercise your blood sugar can go low several hours after exercise, making exercise close to bedtime risky.

OK, so what is the final answer? You must find a time 1 – 3 hours after you eat but away from the peak action of insulin. The larger the meal, the more time you should wait. If you must exercise in the morning, eat something small before starting, such as low fat yogurt, a handful of nuts, something that has some carbs, some protein and some fat.