In my personal experience and in working with many others, prior to activity there may be a mental gymnastics to determine the right amount of insulin and carbohydrate necessary to fuel the body but also prevent low or high blood sugars. The questions you need to ask yourself are:
Where am I now?
Where am I going?
You could think of your body as a car. If you are only going to drive down the block and back, you probably don’t need to fill the gas tank. However if you are driving out of state, you certainly would need to top off before hitting the road. Planning for the amount of fuel you need is the first step. You will also need to consider the intensity of the activity. You probably know driving fast burns more fuel. The same is true in the body, diabetic or otherwise.
Type1 diabetics have a more complex system. In addition to knowing how much fuel you need, you must also consider the amount of carbohydrates in your body relative to the insulin on board – the insulin remaining in the body since your last bolus including the current basal rate. You must also answer this question:
How much carbohydrate do I need to offset the current insulin on board?
To answer that question you will determine five variables:
– When you had your last bolus.
– How many units it was.
– How many correction units/ boluses were taken
– The timing of corrections
– Current basal rate per hour (or total long acting Lantus or other longer acting insulins.)
The amount of carbohydrates is the variable a diabetic needs to know in order to perform well. Carbohydrates provide both energy (fuel in the tank) and an offset to insulin on board. Proteins and fats must also be considered although their contribution to raising blood sugar is less and slower in nature. Diets must take total insulin on board into account. Not doing so is a reason many T1D’s gain weight when they become more active or why they can fluctuate greatly during and after activity. Often times there is an incorrect consideration to appropriate insulin timing and balance prior to exercise which dictates fueling needs.
Below we wil evaluate three timing options prior to your activity and how to determine a pre activity plan.
THREE HOURS PRIOR TO ACTIVITY
Three hours before an activity is significant enough that any insulin you take at this point will have less impact on your planned activity blood sugar. Most rapid acting insulins only affect the body for 3.5 to 4 hours. However, what you do in this extended window will set you up for success in your activity.
Preparation for a your activity requires you to know the total amount of insulin on board. (If you are not a pumper you can find several apps to help track insulin on board.) The total amount of insulin dictates the glucose required for optimum performance during a workout, practice or any physical activity. As a general rule it can be calculated by adding the units of insulin in your basal and last boluses. Optimum performance requires you consume approximately two and a half times the grams of carbohydrates that total insulin covers.
Equations:
Total Insulin on Board = Basal (current per hour rate for pumpers, or total daily Lantus dose divided by 24hrs.) + Bolus + High Blood Glucose Correction Insulin.
Grams of Carbohydrates to consume immediately prior to exercise = [Starting Total Insulin on Board / (Exercise Insulin-Carbohydrate Ratio of 1:(X*2.5)]
Where X = Current IC Ratio*2.5 ….For intensive running your current IC ratio may be multiplied by three.
*Note after calculating the needed carbs to start exercise, one would or could subsequently turn the basal rate to “O” units per hour for the duration of the activity (Assuming you using an insulin pump) for very extended and intensive activities. Consult with your physician before doing so and if you are not pumping you may consider a lower total daily dose of long acting insulin.
A simple example is one unit of rapid insulin being the total insulin on board. That unit covers 15 grams of carbohydrates. If one unit is on board, then 37.5 grams of carbohydrates must be taken at the start of exercise. Failing to do so increases the dangerous risk of falling blood sugars ultimately leading to hypoglycemia.
Even fast acting insulins take time to get rolling, and in the first 15 minutes the action on blood sugar will be very little. Novolog, Humalog and Apidra have similar curves where the peak is approximately 50-90 minutes post bolus. From there the insulin falls off rapidly and has a tail of “lowering action” for up to 3.5 – 4 hours.
In a three-hour window you can take a full bolus and eat a regular meal. In addition to your consideration of diabetes, you should also be eating whole, “minimally processed”, healthy foods. Your food choices based on macronutrients should include 60-80 percent of carbohydrates as compared to the protein and fat content of your diet. Further, the proportion of slow-burning versus fast-acting carbohydrates should be 80-20, such that you eat 80 percent slow-burning or low-glycemic carbohydrates and 20 percent fast-acting or high-glycemic carbohydrates. If you’re planning a longer activity, you could add a quarter cup of almonds and a quarter cup of protein powder. The additional calories will sustain a longer effort.
For example, you could eat a cup of steel cut oatmeal and quarter cup of raisins with two tablespoons of agave nectar would suffice for breakfast before working out. The oatmeal and agave nectar are low-glycemic foods. They are less likely to cause the blood sugar to spike. The raisins on the other hand are higher glycemic and intended for instant energy and alertness. Studies suggest higher glycemic foods can increase oxygenated blood which circulates energy for use during exercise. Additionally, overnight the liver burns approximately 150-300 calories for body functions like your heartbeat, breathing and repairing the body!
3 hours Prior to Exercise Recommendation Summary
– Bolus normally
– Fuel: Consume a meal with 80/20 slow/fast burning carbohydrate ratio
– Keep baseline basal rates running normally
ONE HOUR PRIOR TO ACTIVITY
Approaching the one-hour mark prior to exercise is a critical period. If you are hungry and need to bolus, this will have a substantial impact on your blood sugar. Many insulins peak between 50 and 90 minutes. They will remain active during your entire activity and potentially longer than your workout period.
Timing carbohydrates during this window has a positive influence on exercise performance, yet a negative impact on blood sugar management. If you decide to eat some carbohydrates, the question becomes what to do with your insulin. There are three good options, and they all depend on your insulin on board and carbohydrates needed to perform. Here is where you need to be a forecaster rather than a fortuneteller. It’s the “Know Before You Go” plan. The three options are:
– Consume no carbohydrates. Do not take a bolus.
– Consume good fats or lean proteins. Do not take a bolus or corrections.
– Consume carbohydrates. Take bolus.
Consume no carbohydrates. Don’t take a bolus.
This is the simplest of the three options done at the start of exercise. It does not require any particular change to the regimen until right before your activity. Your primary consideration will be to monitor high blood sugars. Make any corrections at 40 percent of the suggested pump correction factor and turn off the pump basal zero minutes before exercise. (Note if you are on injection therapy you would not be able to suspend the pump and therefore a lower correction percentage can be considered, example 20% of a normal correction.)
Being able to take advantage of this option is the simplest one preceding exercise. It assumes you have no insulin on board from a bolus or corrections taken within three hours before exercise.
Consume good fats or lean proteins. Do not take a bolus or corrections.
Another simple option is to eat good fats or lean proteins in this 60-minute window before exercise. It also does not require any change to the regimen until you’re about to start your activity. You also do not have to take a bolus or make any corrections to your pump.
Eating good fats and proteins at this time will help satiate you and keep your energy level up without spiking your blood sugar. Any insulin on board will not adversely affect your workout after eating good fats and proteins. Both macronutrients absorb more slowly, so they provide excellent long-lasting energy. Examples of these foods are seeds, avocado and egg whites. You will find that this option is great in its simplicity ability to fuel workouts!
Consume carbohydrates. Take bolus.
If you have to eat carbohydrates this close to working out, then eat no more than 100 calories worth. That’s about 20 grams of carbohydrates. Take a bolus for the full amount of 20 grams of carbohydrate. You should not take any more than 20 grams of carbohydrates, because the insulin you take at this time will cause a dramatic reduction of blood sugar during exercise. It will also require you to eat more carbohydrates during exercise. The less insulin you take before exercise, the less you will have to eat during an activity.
Also, it’s a good idea to eat slower-burning, low-glycemic carbohydrates at this time. Eating fast-burning, high-glycemic carbohydrates will spike your blood sugar too fast. The result will make you high at the start of activity.
The key with this option is the size of the bolus you take to offset the carbohydrates. You want to be easy with the bolus and possibly not even take one.
Any corrections in this time window should be half the normal correction amount to avoid significant impact on blood sugar during exercise. Often when someone takes a full correction this close to exercising, they will slip into a low within the first 20 to 30 minutes of exercise. The result can be incredibly frustrating when you’re trying to focus on an important practice or get in a short amount of activity. Taking less correction will bring your blood sugar down slower, as long as you begin exercise soon afterwards.
Know Before You Go
The key to peak performance and managing this critical period is planning. Know when you will be active and plan your diet and consequently insulin needs well in advance. If you know you are going to be active during the day, try to consume a larger portion of carbohydrates well in advance of your intended exercise. This will not only give you enough to take the proper bolus and correction, but it will also give you plenty of time to process enough carbohydrate to perform at your best.
This strategy is similar to the cycling concept of – separating braking and swerving – to safely lean through a turn. Hammering the brakes in the middle of a turn increases the likelihood of crashing. Taking a bolus just before exercise is like braking in the middle of a turn. Following these options will help you separate the braking from the swerving and get you through your activity safely.
30 MINUTES PRIOR TO ACTIVITY
This time window requires similar considerations as the one hour before exercise. The major difference is fine-tuning (If you are a pumper) your basal depending on whether you blood sugar is a little high or low.
For instance, blood sugar between 180 and 200 mg/dl could be managed with a temporary basal rate adjustment increasing 20 percent from baseline for 30 minutes instead of taking a correction bolus. The little bit of extra insulin will help to lower a slightly elevated blood sugar once you begin exercise.
If your blood sugar is more than 200 mg/dL it would be a better to do half the intended correction.
Deciding not to eat in this window could also impact your blood sugar. If you don’t eat and your blood sugar is slightly low, you could reduce your basal rate between 10 and 50 percent from baseline.
If you are not pumping and are on injection therapy, you may opt to consume a small amount of carbohydrate if your blood sugar is lower than 115mg/dl.
Much of what I have been describing in this post is a proactive approach to T1D management. Keep in mind that often life will get in the way of the perfectly setup activity and routine! Be flexible and always carry extra glucose.
The key takeaways are to remember that total insulin on board always dictates how much food you will need! Practicing these principles does take experience and time to hone in on your routine.