Diabetes Nutrition for Endurance 101
I’ve finally got in touch with a professional who is helping me to systematize my endurance nutrition strategies, with the specific focus of safely navigating endurance events with type-1 diabetes.
In previous posts I have explained my ways around this, ad I was happy to see that they did not go too far from the guidelines a nutritionist has provided me. Although there’s always some subjective variables coming into play, there are facts that must be taken into account.
Basic Facts You Must Consider
So let me clear the horizon of my subjective takes, and put some hard facts on the table that everyone can use to build up their race nutrition plan.
The higher the intensity of the exercise, the greater the glucose consumption, the lower the insulinemia.
The goal is to have starting with a good BG (120-180), and ending with a good BG (120-180). To do so, we must know:
Our starting blood glucose,
How much insulin we have on board,
How many carbs we need prior to and during that particular physical effort.
Then, we assess what to do and eat depending on our starting BG level.
If between 120-180, all fine. You may have a quick carb snack, determining the amount using the formula*.
If < 100, we take carbs to avoid a low. The formula to calculate the grams of carbs is below*,
If > 250, avoid carb before the activity starts.
Insulin Management
With regards to insulin:
If your BG is high (around 200) within 2 hours of the bolus and your snack, that is normal and activity will take care of it.
If BG is high far away from meal time (high fasting blood glucose), it is better to inject some insulin.
PRE - race insulin management
If you need to eat something before the race, split your meal (ideally a mix of complex and fast carbs) in half. Then,
Eat the first half two hours before, with only 50% of your bolus.
Eat the second half right before go-time, with no bolus.
DURING race carb management
No insulin here, only carbs management. Aim at 30-60 grams of carbs per hour, depending on the length and the intensity (the longer and more intense, the more you should get)
POST- race insulin management
Bolus: reduce by 25% - 50%, depending on the intensity and the lenght/duration. You will always be more insulin sensitive after physical exercise.
Basal: reduce by 25% - 50%, depending on the intensity and the lenght/duration.
Carbohydrates Management
It is very useful to know how much carbohydrates increase blood sugar, because that gives a clear indication of how much we should eat depending on our starting BG, and how much we can expect to integrate during our efforts, depending on their intensity.
To give some background: the glucose present in our body is found in the plasma and in the extracellular fluid (about 20 g of glucose, of which 2.5 g in the plasma and 17.5 in the extracellular fluid) and this corresponds to about 25% of the body weight.
So how many carbohydrates should you take? That depends on how much your blood glucose is likely to drop in the first 30-40 minutes of activity. The Formula is to calculate that is:
Carbs (g)/ (25% of bodyweight) x 100 = delta of blood sugar in mg/dl
Let’s use an example: how much blood sugar increases with 10 grams of carbohydrates, based on the body weight? The formula takes both factors into account
Weight/4 = extracellular fluid (equal to 25% of body weight)
Grams of carbs taken
I weight 65 kg and take 10 grams of carbs, so I can expect my blood glucose to be impacted by 10/(25%*65)*100 = 61mg/dl
Let’s take another example. The glycemic target ahead of starting an activity is in the 120-180 mg/dl range. I weigh 65 kg and my blood glucose before heading out for my long run is 100. I want it to be higher, around 160. How many carbs should I get to reach that level?
If the starting blood sugar level is 100, I start to exercise and I know that my blood sugar level can drop by 60 mg/dl in the first half hour.
The formula is always the same, with a slight variation to account for our target blood sugar level:
Target blood sugar level - current blood sugar level/100 x (weight kg/4) [(160-100)/100] x (65/4) = 9,75 g
So I must eat around 10 grams of carbs in order to have a “glycemic safety margin” that allows me to avoid the drop of blood glucose in the first 30-40 minutes of activity. Then, to keep it up during the run, I will consume around 45-60g of carbs each 45 minutes of exercise.
I hope this raw, technical post gave you some food for thought to review your insulin and carb management, discussing it with your physician. This was also the topic of a recent video I have posted, should you prefer to explore some other format.
Let me know your thoughts, your experiences and definitely share how you’re managing your insulin and carbohydrates while exercising, I am always curious to know! See you next week!
