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Exercise effect on blood sugar - fed vs unfed

S

Sapien

Well-Known Member
Messages
140
Location
United States
Type of diabetes
Prediabetes
Treatment type
Diet only
Since I started testing my blood sugar at home, I have noticed that it drops more during exercise if I have recently eaten some carbs than if I exercise on an empty stomach.

One day I tested in the afternoon 4 hours after last eating and was at 5.2 mmol (94 mg/dL). I ate a sandwich with whole grain/seed bread and almond butter. (Bread 34 g net carbs, 10 g fiber). I waited an hour and tested at 6.1 (110). Then I exercised (sprinting then walking in intervals for about 30 minutes. I tested after exercise and blood sugar was 4.0 (72).

The next day I tested about the same time and was 5.3 (95). This time I ate nothing and did the same exercise routine. Afterwards my blood sugar was 5.0 (90). Barely changed.

Has anyone else experienced a similar phenomenon?

Previously I noticed that when I exercise in the morning (fasted) that I see little change in blood sugar, but in the evening (usually after some food) my blood sugar drops substantially after exercise.

It seems like eating some carbs puts my body into sugar burning mode.
 
I do love me some interval running. Interesting. I'm not sure how I can try this experiment with such an inability to process carbohydrates.
 
I can't do any strenuous exercise without raising my levels. I can walk and nothing much changes, maybe a small drop, but housework or gardening makes me rise.
 
Sapien said:
It seems like eating some carbs puts my body into sugar burning mode.
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Hi Sapien everybody is different and for some the best time to exercise is in the evening.
For some people exercise increases there bg levels.

You didn't say what your looking to achieve through exercise?

If it's just to control bg levels and burn off any excess sugar
Then eating carbs before hand is like overfilling the bath and having to pull the plug out to let half the water back out.
Yes you have got rid of half the water but the same result would been achieved by putting less water in the bath to begin with. (water is sugar/carbs for the purpose of this heavy handed analogy.)

If your looking for weight loss.
Exercise on an empty stomach forces your body to break down fat stores to fuel the muscles, you might find it raises bg levels but that's a good thing as the only place the additional bg can come from is breaking down fat converting it to be used as fuel for the muscles.
Using the bath analogy again its like a dripping tap evidentially it will fill up and overflow if the plug is in (eating carbs) but if the plug is out even though it never looks like it you have used a bath full of water.

OK that's it I managed to explain Gluconeogenesis using a bath tub and a leaky tap.
(well sort of )
 

I am looking to better control blood sugar without losing weight. I am a bit too thin. I am doing more resistance / weight training and going for more HIIT instead of longer runs.

I was really surprised that when I eat carbs before exercise my blood sugar is lower after exercise than when I don’t eat before it. I would have expected to see my blood sugar lower when exercising on an empty stomach.

Since I started testing, I have been surprised how high my blood sugar can spike at 30 minutes (once with lot of carbs up to 10.0 (180)!) although it usually comes down rather quickly and at two hours it is usually 5.9 (106) or less. I would like to stay below 6.6 (120) at all times and get my fasting blood sugar back to 4.5 (82) or so. It had been creeping up and was 5.7 (102) on one lab test which is in the pre-diabetic range. The trend wasn’t looking good. The most recent test was 5.1. (92), but I still see readings in the upper 5’s some days testing at home. Most days in the lower 5s. (Home meters aren’t perfect so I try to look more at the trend than the actual reading)

I tried going really low carb for a little while but I lost too much weight and it didn’t seem to help lower the fasting blood sugar much. I think it actually raised it a bit.
 
I have a possible explanation for this but am very willing to be told that it is incorrect. T2s and prediabetics tend to be insulin resistant, so they produce a lot of insulin to bring down their blood sugars when they eat. Exercise makes you less insulin resistant, so if you eat and then exercise the insulin pumped out for your food gets used more efficiently and hence your blood sugar goes down.
 
Interesting theory - I like it
 
Low carb eating will raise fasting levels as your liver starts to empty itself while you are producing less insulin in response to the low carb diet. It's not a bad thing. Diet Doctor website has an article about it.

I noticed the bigger drops in bs after a carb hit too. I thought it meant I was getting closer to having reactive hypoglycaemia. Which would not be a good thing.

I think finding your levels not dropping much on an empty stomach is again to do with not having asked your body to produce insulin (in response to a carby meal) but by eating nothing, your liver will start to free up its stores and keep your level from dropping but your bs might rise if there is not much insulin floating around to deal with it or if the liver is so full it releases large amounts of glucose but being insulon resistant, your cells can't absorb it and so it stays in the blood... Something like that anyway.
I would think the second scenario (empty stomach) is going to rid your liver of the excess faster and in the long run will lower the fasting levels eventually.
Continuing to eat carbs won't allow the liver to empty its stores anywhere near as fast.
 
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I had another interesting reaction to exercising on an empty stomach versus after eating some carbs (fruit).

Yesterday, I ate a relatively low carb lunch around noon then exercised at about 5:30 pm. No food since lunch. BG before exercise 93 (5.2) and after 102 (5.7). After I ate dinner my BG dropped to 95 (5.3).

Today I ate a little more than a cup of fruit at about 4:30pm. Exercised again at 5:30. BG before exercise (1 hr after fruit) 120 (6.7) and after exercise 63 (3.5). Hypoglycemic?

Once again my blood sugar drops quite a lot when exercising after eating carbs, but rises (or barely drops) when exercising on an empty stomach.

Exercise was alternating running at 8 mph and resting by walking at about 4 mph for about half an hour.

Strange reaction?
 
Sapien said:
Once again my blood sugar drops quite a lot when exercising after eating carbs, but rises (or barely drops) when exercising on an empty stomach.
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Hi Sapien, you don't seem to be quite understanding how this works.

  • Empty stomach: your body has to produce its own glucose as fuel which means, you burn up body fat.
  • After eating carbs: you body already has a fuel source and does not need to produce anything means, you do not burn up body fat.
It takes approximately 1&1/2 hours of weight lifting to burn of a pizza, it will take about 2 hours before your're body starts to eat into its own fat supply for energy.

IF you wan to loose weight do the same exercise on an empty stomach. Simple.
 

I noticed something similar after eating carbs just after I was first diagnosed with gestational diabetes and was still working out what I could eat. Something that spiked me to 8 or 9 mmol dropped me into the 3s once, whereas after the very low carb options I would only ever return to 4s or 5s.
But as the pregnancy went on and my insulin resistance went up, the carb foods that would spike me to 9 mmol at one hour left me at 7 or 8mmol at the 2 hour mark and the crash back to the 4s came much later, after another hour or two for example.
I wasn't exercising much but growing a baby does count as something taxing on the body and burns up your stores pretty fast. I was effortlessly in ketosis most nights towards the end of pregnancy if I didn't snack through the night.
 
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I think you will have to first empty your glycogen stores before you start burning fat.
 
I am not trying to lose any weight. I am trying to improve glucose regulation (lower fasting glucose and keep post-prandial from spiking). I am trying to figure out what I can eat to keep BG below 120 (6.6) at all times and move my fasting down so it stays consistently below 90 (5).

Weight training seems to have little direct immediate effect on my blood sugar. Hopefully it helps lower fasting blood sugar over time.

Aerobic exercise seems to have an immediate effect on my blood sugar, but like I say I find it odd that eating carbs before seems to make the aerobic exercise dramatically lower my blood sugar, but doing exercise on an empty stomach can increase my blood sugar.

(Interestingly I feel just fine with my BG at about 60 (3.3). I checked with two different meters to confirm.)

Does that mean that carbs put my body in glucose burning mode? And blood sugar keeps dropping even after the carbs I ate have been utilized, but exercising on an empty stomach I am more in fat burning mode and my body doesn’t use sugar that my liver releases (from the stress of exercising?) since muscles are burning fat? So the blood sugar rises some even though I haven’t eaten recently.

I would have thought that exercising on an empty stomach my muscles would use up glucose stored in the muscles then from the liver and only after the glucose stores are used up start burning fat. If the glucose stores are used first wouldn’t my blood sugar be at least as low exercising fasted as non-fasted?
 
Mr_Pot said:
I think you will have to first empty your glycogen stores before you start burning fat.
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I see where your coming from Mr_Pot, but it's just diminish not deplete. You do not have to empty the muscles glycogen stores completely before the body starts to replenish them.

Otherwise all those people who running around saying I gave it 100% would be dead.
 

I think you might be better focusing your thoughts on insulin production; if you eat carbohydrates then your body will produce insulin to control your blood glucose (BG) levels.
If you are insulin resistant then there may be a delay before your BG level starts to come down and you may over produce insulin.
The result is then that you end up with too much insulin and your BG goes lower.
This in turn may prompt a bit of a liver dump to bring your BG back up.

So what I think is happening is that you are eating carbohydrates, producing a bit too much insulin, then undershooting a little.

If you are not eating then there is no carbohydrate to process and not much insulin being produced so your BG level should remain relatively stable at rest and at exercise.

I think the fasted exercising is probably better because the carbohydrate (if you have a time lag before the insulin kicks in) will be spiking your BG levels which is not good. A steady but slightly higher BG level is probably better than a spiking then slightly lower BG level.

The end BG level is usually less important than the process you go through to get there.
 
Sapien said:
keep post-prandial from spiking)
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Simplest way to do that is eat less carbs and fruit.

Muscles continue to burn fuel for 24 hours after you finish exercise. To see what effect you are having by increasing carb intake try one week with carbs before hand and one week with out and see what overall effect it is having on you.

Sapien said:
since muscles are burning fat
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I think you might be getting confused there (or I am) muscles don't tend to burn fat ketogenesis but rather they replenish there glycogen stores from the glucose in the blood stream. When we say "burning fat" we realy mean breaking down fat stores into glucose.

I realy wish I could give you the answer your looking for here @Sapien but good luck with it all.
 

I think that is a good idea to test for one week each with and without carbs pre-exercise to see the effect, rather than changing day-to-day. Thanks.
 
Sapien said:
I think that is a good idea to test for one week each with and without carbs pre-exercise to see the effect, rather than changing day-to-day. Thanks.
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Following up on my original responses, I've just fitted my first Freestyle Libre blood glucose monitor and I'm seeing some unexpected things.

One is that my BG level seems to rise steadily during the day when I'm just having coffee, butter and cream.

The second is that if I exercise on the above, my blood glucose continues to climb when I though that it would drop.

Third is that when I eat my one meal a day at around 18:00 my BG spikes (not unexpected, although I didn't expect it to go quite as high) but my BG then drops down below the daily (slowly climbing) average and bottoms out around midnight. My BG then starts to slowly climb back up.

So I am going to test if a small meal early in the day has the same "boom and bust" effect which then resets my BG to a lower, slowly climbing, level.

So I am now considering if a spike first thing will actually be beneficial in my case.
I will need a lot more data, but things are not as straightforward as I thought.
 

Hi littlegreycat, could you put this on a new thread do you think so it doesn't get lost in this one? I am fascinated by your post and I would be really interested to see how you get on and the story the libre tells you. I would love a libre but am currently relying on finger pricks and guesswork! x
 
Hi Sapien,

Have you had your exocrine pancreatic function checked for EPI? It is often overlooked, but many with diabetes will suffer from some level. It was the EPI effects of nutrient deficiencies that were the biggest cause of the wild glucose swings (much higher than the ones you mentioned) with me.
 
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