Exercise, weight loss, exogenous insulin

Type 1 and LADA
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Question for the group: is aerobic exercise with zero carbs and zero IOB better in terms of burning fat and weight loss?

Used to be my habit to do my daily bike ride in the afternoon, partly to get the aerobic power-boost to my lunchtime bolus. But it’s really a PITA to make that balance come out right, and since I’m retired and can pick my times I’ve recently switched to going pre-lunch, eliminating carbs and IOB from the picture. Simplifies things a lot, but I’m also wondering if I’m getting more benefit from the exercise in terms of fat burn. Does having exogenous insulin in your system cause you to burn more carbs than fat, inhibiting the effect of exercise on weight loss? I tend to get plateaued at a certain weight and it’s really hard to convince my body to get unstuck. It seems like the change has had a salutary effect in this regard. Anyone know?

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In general, having less insulin will down-regulate the storage of fat (lipogenesis) and up-regulate the creation of liver glycogen from non-glucose sources (gluconeogenesis).

So both of these things will contribute to weight loss.

The fuel sources we use during exercise are determined by a number of things though, not just how much insulin and carbs are available.

Your pre-exercise metabolism, your fitness, the exercise intensity, and what fuel sources are readily available will determine what you use. It’s not a simple enough process to say that doing one thing results in another thing happening.

But if you want to make a very general statement, having less carbs on-board and less insulin on-board before exercise will make fats the easiest fuel source for your body to access, and will ultimately help your weight loss.

This can happen fairly easily in aerobic exercise, as long as the exercise intensity is not so high that fat becomes inadequate for your body to fuel the activity.

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I’ve been having the same kind of questions. It seems I hit plateaus in my weight loss, but I think overall I’ve done pretty well with my current plan. I have a tight, healthy diet, plus my daily workout at lunch. I’ve been getting to the gym at noon and skipping lunch. I do have a good, nutritious breakfast for which I bolus. I place my pump in Target Temp Mode, which should keep my BG under 140 before my workout. It works really well and I rarely get a low, even with heavy cardio.

I’ve lost around 87 pounds since ladt summer and am almost at target weight.

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Exercise does not provide the kind of drop in BG numbers as it does for Type 2 diabetics. It does however burn calories, and can be part of a weight loss plan.

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Just clarifying, did you mean to say not as much for Type 2 as for Type 1? Because managing that drop has been a lifelong struggle for me as a type 1.

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Type 2’s benefit the most from exercise. As per my endo, Type 1’s not so much. Nevertheless good for you. Just not the panacea we would like to keep our numbers in check.

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I don’t mean to read into someone else’s comments, but perhaps this is a different way of saying what was meant by the comment :arrow_up: above?

For T1’s, exercise does not provide the kind of drop in A1C numbers as it does for Type 2 diabetics.

That would make sense because while T2’s suffer from insulin resistance - which exercise helps reduce - T1’s don’t have as much of a problem with insulin resistance as they do with the problem of having no insulin (other than what they take).

If a T1 and a T2 made no other changes besides adding exercise, the A1C of the T2 would probably be reduced more from exercise alone, than for the T1.

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Yes!

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Oh, I get it. Right you are on all points (including that minimizing resistance is a good thing for T1’s too, as far as that goes, but not the original root problem). My post was all about immediate exercise effects so I didn’t catch the shift of context.

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A side note to this discussion…

The rate at which a person burns calories depends on many things - the size of the person, the type of activity, the person’s metabolism, their fitness economy, the intensity of the activity, etc.

Running, swimming, and cycling are all a little different. But for the sake of the point I am making here, we can just say they are all “close enough”.

The amount of blood a person has and the amount of liver glycogen a person has also depends on a few things, mostly the size of a person. But just assuming some easy numbers that are roughly average… an average person might have about 4 grams of glucose in their blood, about 100 grams of glucose stored in their liver, and about 500 grams of glycogen in all of their muscles.

Again, this depends on many things, but here is just a general ballpark average to give context of it all (“hard” for some people is not necessarily as hard for others).

If we are only talking about using a single fuel source, and talking about an average sized person running hard:

  • They would burn through their blood glucose in about a minute!

  • Using only their liver glycogen, they could go 25 minutes.

  • And using only the muscle glycogen in their legs, they have about 1 hour.

When you slow down and start using fat, you increase the time greatly. And if you slow down a lot and start using almost entirely fat, you can pretty much go forever (until sleep and muscle exhaustion and dehydration take over).

I wanted to add this to the discussion to illustrate how insignificant the sugar we have in our blood is, compared to everything else!

Our liver is constantly providing fuel to our blood. And our liver is constantly storing fuel and creating fuel.

BTW, muscle glycogen can never raise blood sugar! Once glucose is stored in the muscles as glycogen, it can only be used by those muscles. It can never be used to raise our BG, and it is never shared with other muscles.

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That’s exactly why I exercise in the mornings after having some coffee but I don’t eat breakfast, only lunch and dinner. For me, this regimen is really effective for weight management and for not having the craziness of blood sugar swings that come with exercising after meals with IOB. I can’t say enough how glad I am I can do this and how effective it is for me. I don’t know hardly anything about the keto diet, and I’m not a fan of fads so I don’t know much care about it either, but to the extent I understand it, I have wondered if exercising without short-acting insulin IOB is better for weight management due perhaps to some kind of keto effect. Either that or it doesn’t matter, and I definitely don’t think it could make things worse. But that is just my experience. Good luck! Keep up the exercise! Yay, retirement!!

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I’m posting this question here in hopes someone who knows the answer may see it. I’m going to have an InBody 570 Body Assessment tomorrow. Is wearing a pump or cgm an issue? It didn’t mention it in the material they sent me, but I read you shouldn’t have a Pace maker or implanted device.

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I’ve always understood very simply that as a T1 if you havent eaten and dont have insulin in your system then you start to produce ketones, and the ketones are produced by burning fat. If your BG is high and you have ketones you shouldnt exercise, because another chemical reaction happens which can be quite dangerous (can’t remember off hand) but providing your BG is fine it would seem that exercising without insulin and food on board would be most effective in burning fat.

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All good points. Of course I’m mostly using IOB to refer to bolus as opposed basal insulin. Though I do sometimes suspend that too if it’s pulling me lower than I want during exercise.