Reactive hypoglycaemia

Might be one for @Dr_Alex_Harrison but interested if anyone else has experienced this.

What is the advice around this? I recently changed up my nutrition to more what science says but its not been working. I decided to buy a glucose monitor to see if what i was feeling was what i thought. Unfortunately it was.

Today i had a mixed meal breakfast of around 1.5g C per kg 75g C and 40g protein and 20g fat. Left it 1.5-2 hours as recommended to digest and basically walked out the door and bonked. Went back in tested my glucose levels and they were 4 not optimal. Obviously, i hadn’t run out of energy as breakfast was a good 700kcal and did nothing bar sit on a chair and work between that and going out.

So how do you work around this? I feel great on a low-carb breakfast but its crap for performance. Low carb breakfast then carbs just before and lots during and after to replace glycogen?

I get this if I wait too long before I get out the door (or if I eat too much) but it totally depends on the carb. I believe some people are more susceptible than others with particular carbs

My consistent breakfast is 0.5-0.75 cups of quick cook oats, toppings = 1tbsp peanut butter, 3tsp brown sugar, half banana.

I eat this 1-2hrs prior. If it need to jump on the bike within 30mins, I have a cliff bar

I seem to be more sensitive to rice or cornmeal and certainly have bonked hard having a chocolate bar within an hour of exercise

I would experiment with foods and timings and always have some sugar/gel etc in your pocket to top up if you get it wrong :blush:

Generally you don’t want to eat within about 15-90 minutes of training. Either eat something simple 15 minutes before beginning or wait until after this window. The more fat and complex carbs you eat the more this may extend beyond 90 minutes. It sounds like for you it was too soon after eating. 700 cals is quite a bit to clear your system. I would try eating a smaller amount (maybe 400-500 cals) and longer before training or eating foods that digest easier. Once you start training, if you will be training for more than about 90 minutes, start consuming carbs early in the workout and continue throughout the workout.

Waiting till after doesn’t seem to work and only makes matters worse, i.e. even lower.

I agree it seems silly that 700 to clear the system, its clearly in the muscles but something else is at play. Maybe the devil is in the dosage.

That said if reducing the size of portions works that great but still have to get the overall daily kcals in and or carbs somewhere with constant ups and downs!

It might just take time for your body to get used to the extra nutrition at that time. It took me over a year to feel good after breakfast, I never ate much that early before.

Maybe make smaller, more gradual changes.

I was in the same boat us you. I would feel very sluggish in the first 30… 45 minutes and then things would improve.

I now take my breakfast already with my cycling gear and water bottle top up. The trick for me, is to be peddling 5 min after I finished breakfast. - not a big meal

If my workout is at 10am and I awake up at 6am, I’ll not eat (just coffee) until I’m ready to leave the house.

This was one of my biggest nutrition improvements.

What sort of intensity was the ride and did you get an appropriate warm-up?

It was supposed to be 2 hours with 2 sets of 4 x 30 sprints, but i couldn’t complete it due to feeling awful.

Yeah i am starting to think this might be the best bet. Had a few rides really early morning like 6am and just got up espresso bowl of rice and banana and out the door and felt great.

That or a low carb breakfast, eggs, avo etc then banana / simple sugar just before hopping on the bike at 10/11am. I seem keeping blood sugar stable is almost more important that the energy in the food?!?!?!

My worry is this goes against all the traditional science of fuelling… :laughing:

I’ll not pretend that I’m an expert but insulin rebound is a true thing - is science! :smile:

I read somewhere here in the forum about it and that was a light bulb moment for me💡

Yeah, if riding later in the day have you experimented with lower carb until the ride?

I’m still trying to find what works for me during the week (I ride after work)

I’m always eating (every 2 or 3 hours) and I’m finding difficult to manage this. At the moment I have a “big meal” 3h prior and then a small snack just before the ride. It works MOST of the time. But I can’t always have that meal 3h before and then I’m just starving.

At the moment I’m trying to do the workout early in the morning before work (my 4 month old son is helping me to awake up).

I’ll fiddle with the low carb meal, never tried.

Interesting, i feel great and consistent energy on low carbs at breakfast so i guess it makes sense unless riding straight away to stick to that. Have a high carb snack just before the bike then all the carbs at dinner to refill glycogen where the effect shouldn’t happen as bad and or doesn’t matter as you are sleeping.

I think i remember reading you are less insulin sensitive in the evening.

I have to admit my main problem at the moment is im trying to increase intake but the more you put in meals the bigger the crash and i do not have the time to be eating 6 times a day / dont really believe that wholey healthy for the body. Need some rest and digest time.

I can’t vouch for any of its scientific claims, but this article touches on what you and others have commented on in this thread. Keep in mind that the company sells sports nutrition products, but I think the general advice is good.

In summary, it recommends to either consume calories right before exercise or wait three or four hours after a meal. I think there is individual variability in what is tolerable, so your body must be on the sensitive side. You may not be able to get away with eating in the middle of that pre-exercise window.

Great article and this does seem to go along with that i’ve felt.

Today rode early morning, quick bowl of rice and banana 10 mins before jumping on the bike. No crash ok energy!

My next question would be obviously we love the carbs and this proves im very insulin sensitive. Im only training once a day so to stop the post ride crash (if i consume a large portion of carbs then 70g+) its fine to save them for the evening when you are naturally less insulin sensitive. Almost backloading for the next day. Like the bedtime oats.

I started doing this long before I started cycling for weight management. It helped me to lose 20% of my body weight. Not just this by itself but this helped me to manage cravings.

It’s easier for your body to process small amounts than a big meal at once. It also helps to have more nutriants variety (more meals = more chances of different foods)

I’m not advocating that eating every 2 to 3h it’s for everyone, but it shouldn’t be dismissed as viable strategy to achieve a goal.

Yeah i get it, i just haven’t got the time in my day to be eating all and keep grabbing stuff.

1 Like

Just slam carbs closer to the workout, in liquid form. 50-80g carbs 15-20min prior is better than 100g carbs 1hr prior.

Eating anything in the 30-75min window before workout, followed by no consumption 0-30min pre-workout, is a recipe for reactive hypoglycemia.

As I’ve shared elsewhere:

Common symptoms of mild/moderate hypoglycemia:

  1. Fatigue/exhaustion
  2. Inability to complete routine exercises/tasks
  3. Intense Hunger
  4. Nausea or stomach discomfort/pain
  5. Shakiness
  6. Lightheadedness
  7. Weakness
  8. Sweating
  9. Irritability
  10. Tingling sensation around mouth, feet, or hands.
  11. Generally feeling like you’re dying (maybe that’s just me??)

Common causes of hypoglycemia:

  1. Rebound hypoglycemia, ie. blood sugar crash. Most commonly recognized in children after they eat candy, run around like crazy and then start wailing. Ironically, the same thing happens in adults, we just (usually) don’t cry about it. The surest way to induce rebound hypoglycemia would be to consume a high glycemic index meal 40-70 minutes prior to exercise, and NOT consume any high glycemic index foods during exercise. Even in cases of more moderate or low glycemic index food consumption in that time window before exercise, rebound hypoglycemia is remarkably common. Another common way to create rebound hypoglycemia is to either consume too little intra-workout carbs during a portion of training, or to delay post-workout carbohydrate consumption by more than 10-15 minutes especially if intra-workout carbohydrate consumption was on the lower end of the spectrum for the work output or duration of exercise.

  2. Intense exercise in the absence of carbohydrate or minimal carbohydrate. Work out for long enough or hard enough, without sufficient carbs, and you’ll surely begin to experience mild hypoglycemia.

  3. Prolonged period of no food consumption. Don’t eat for 12 hours, and you’re likely to experience some level of hypoglycemia as your body works hard to run in a low carb environment.

How to prevent it:

  1. Don’t eat 31-75 minutes prior to exercise.

  2. If you must eat in that dreaded window, be sure it’s a balanced meal, low in fat, AND ensure that you have intra-workout carbs during your workout and are actively drinking them IMMEDIATELY from the onset of exercise or even just before you start, and throughout the entire workout.

  3. If you need to eat closer than 90 minutes to your training, try to do it 10-20 minutes before training, and make it something very easily digestible (like intra-workout carbs) so that it’s not sitting in your gut doing nothing while you train.

  4. Ideally, eat ~2 hours prior to training. The more complex the meal is, with more fat and more fiber, the longer before training is advisable.

  5. In cases of workouts lasting 75 minutes or more, you MUST have intra-workout carbohydrates, or you’ll surely risk the onset of at least mild hypoglycemia by the end of your training session.

How to FIX it, if it happens:

  1. If you’re in middle of workout, drink 10-50g of carbs depending on how much you have left, and how far behind you are on your “scheduled consumption” assuming the target was to drink steadily until the end of the workout, at which point, you’d be out of intra-workout carbs.

  2. If you’re not training, reduce activity level (sit) if possible. Drink 4-12oz water, depending on thirst, and consider moving all or part of the next meal’s healthy carbs to right now. Wait 20 minutes. If it persists intensely, consider adding 20g more healthy carbs, or moderate-moderately high GI carbs like banana, melon, mango, white rice, skim milk, most breads.


This one is interesting as for me it seems to get worse the longer away even with a big mixed P/C/F meal. Say around 700-800kcal.

Like to said above the only way it seems to work is to eat and jump on the bike or eat mainly protein/fat then slam some carbs again just before the bike.

I also wonder if insulin sensitivity and leanness come into place as in the morning you are supposedly more insulin sensitive so adding that to being quite lean and even more insulin sensitive might create a recipe for reactive hypoglycemia.

1 Like

It does. I believe you’re right, though I don’t think I’ve seen studies on this particular thing. My experience with clients and my own personal experience, as well as what I know of physiology, all tend to agree. (I’m a sport physiologist, not MD).

When I intentionally gained weight to 240 pounds and was up to ~15% fat I was virtually immune to it.

At 9-10% fat at 225 pounds, I was highly sensitive.

Now at 9-10% fat at 208 pounds, I am slightly less sensitive to it, but the period of weight loss from 225 to 208 was the most marked time of sensitivity.

More muscle and less fat definitely results in higher likelihood of reactive hypoglycemia symptom report, and increased severity. Current kcal deficit augments further.

Really? So if you were to finish your meal at 2 hours 15 minutes prior to your first pedal stroke, you’d anticipate worse? What is your food selection like? What specifically are you eating?

Typically if folks are eating pretty hearty (high fiber, high fat, high protein, high volume carbs) meals in the 1.5-2hr window it can act similarly to the more stereotypical “you ate in the 30-75min pre-workout window.”


If folks are moving their meal time further and further away from training and finding that it just gets worse, they’re often folks who have a rapid gut transit, and who would be expected to have a higher insulin sensitivity, and may be choosing lower fiber, rapidly digested food sources. ie. quick oats with sugar, egg whites, banana, carbs in beverage form, etc. This problem would be exacerbated by being VERY lean or running a kcal deficit currently.

I’d be happy to help troubleshoot here. Always interested in finding cases that don’t fit my current understanding! (I’ve worked with 1300 folks one on one, so congrats in advance if you find something I can’t solve).

1 Like