One thing I’ve said over and over is that diet and exercise are two of the best ways to help extend your life and increase the quality of life too.

The good news is a lot of my patients (as well as people who listen to my podcast and read my blog), are listening to what I’ve got to say.

I’m happy people are exercising and eating well, because they’re both inexpensive and you can do them anywhere.

With that being said, I wanted people to be aware that there are ways to make seemingly healthy exercise routines backfire on you.

It doesn’t mean you should stop exercising. Instead, you really just want to focus on proper recovery between intense exercise sets as well as incorporating more zone 2 cardiovascular exercise into your routine.

Today, I wanted to warn you about overdoing it on HIIT exercises.

If you’re not familiar with it, I’ll explain what it is… and regardless of if you’ve heard about it or not,  I’m going to inform you on its potentially damaging relationship to your blood sugar.

Fortunately, if you do HIIT in the right amount and at the right time you’re going to do yourself a ton of favors for your health AND you won’t negatively affect your blood sugar.

How HIIT Can Negatively Affect Blood Sugar

One of the subjects I’m best known for is my focus on hormone health; specifically my focus on thyroid hormone as well as insulin and blood sugar.

HIIT exercise can have an adverse effect on blood sugar by causing your body to produce too much insulin which leads to chronically elevated blood sugar levels.

To understand how this works you need to know how HIIT can mess with your body.

First, HIIT stands for “High Intensity Interval Training”. And to be honest, when you do a HIIT routine it feels like you’ve been hit in the face with a fist!

HIIT has been touted as a miracle form of exercise because it doesn’t take a lot of time and the intensity makes people feel like they’re doing a lot of work in that short time domain.

In a HIIT workout you exercise for roughly 10 to 60 seconds and then you rest for roughly the same amount of time. You then repeat this anywhere from 5-10 times to get the full effect.

Exercise companies, like Peloton and Crossfit, rely on this kind of work to train their clients.

The documented effects of HIIT exercise include boosted metabolism, the promotion of lean body mass as well as improved fasting blood glucose and insulin sensitivity.

Now I know that I said HIIT can be damaging to blood sugar, and this makes it seem like it’s not.

So here’s the rub with HIIT.

Because of the intensity, HIIT stresses your body to the point where your sympathetic nervous system response is turned on. Your sympathetic nervous system is what regulates your body’s fight or flight response. And when you do a HIIT routine and your fight or flight response has been switched on, all of the sudden your body is trying to deal with stress in a number of ways.

The main way it does this is it releases cortisol, and a lot of it.

Cortisol is one of the main hormones your body uses to help modulate your stress response and it can be problematic when you have too much of it coursing through your body for too long a time.

And now I’ll explain how HIIT + Cortisol = Bad Blood Sugar.

How HIIT + Cortisol = Bad Blood Sugar

How is it that exercise could elevate your cortisol levels and produce long-lasting effects on your blood sugar?

When it comes to HIIT and cortisol your body will release cortisol to help breakdown fats and carbohydrates to produce a rise in blood sugar for immediate energy.

When you’re doing HIIT several times a week then it may result in elevated cortisol levels that don’t come back down.

And here’s why that’s a problem.

As the newsletter Today’s Dietitian writes:

“Under stressful conditions, cortisol provides the body with glucose by tapping into protein stores via gluconeogenesis in the liver. This energy can help an individual fight or flee a stressor. However, elevated cortisol over the long term consistently produces glucose, leading to increased blood sugar levels.

Theoretically, this mechanism can increase the risk for type 2 diabetes, although a causative factor is unknown.1 Since a principal function of cortisol is to thwart the effect of insulin—essentially rendering the cells insulin resistant—the body remains in a general insulin-resistant state when cortisol levels are chronically elevated. Over time, the pancreas struggles to keep up with the high demand for insulin, glucose levels in the blood remain high, the cells cannot get the sugar they need, and the cycle continues.”

Well, I’ve written about cortisol before and what it does to your body.

And when you realize that it’s very easy to overdo it on HIIT because you can get a lot of work done in a short time and your body generally quivers after the workout as a result of how hard you worked… you can see how it may lead to excessive cortisol.

And this is why you might want to do HIIT sparingly.

Now I should say that this isn’t universally true.

If you have the time and ability to recover after your workout by doing things that activate your parasympathetic nervous system you could manage HIIT daily because you’re neutralizing the rise in cortisol levels.

But if you live a hectic life, that’s already got you stressed to the max, then I’d argue HIIT should only be a small part of your exercise regimen.

Whatever you do, make sure to consider exercise as a way to help positively impact your health. And, be sure to read our disclaimer on how you should always consult your doctor before beginning any exercise program.