Glucose efficiency improving

First, this is my second true season being a cyclist. I did some cycling before but only to support my motocross racing and even then it was maybe 2-3 hours a week.

Fast forward, I was in decent shape last summer (avg of 8-11hrs/wk on the bike), can’t give you any power numbers as I didn’t have any way to measure, but more or less took the winter completely off from cycling. Stayed in the gym and gained more weight/muscle than I should have.

The 2018 season rolls around and once again I hit it hard in the summer. Ended up winning WORS Cat 2 sport MTB series which has ignited the fire. I now have a Kickr and will be using TR throughout the winter to not only come into the season ready, but improve my fitness. This has also inspired me to really get my diet in order. I am down from 170lbs to about 158 from the end of August (I had been losing weight all summer but this is when I started tracking it).

I am currently at the end of week 3 of SSB mid volume 1. Curious to see what you all have to say about glucose efficiency improving in this 3 week period. I am no longer getting those, stomach feeling like its going to eat itself, feelings while on the bike. I have recently tried to make a smarter choice in what my food choice is going into the workout. As of recently it has been a whole grain cereal with little (6-8g) of sugar and around 10-12g of protein with about 30-40g carbs and more fiber than what I would like but it has not been an issue. Also should note I am in the transisition of moving my training to the morning so I can incorporate weight lifting a few times a week in the afternoon. Today I was able to complete Antelope without really feeling hungry. I believe my FTP is set correctly as SSB feels hard but manageable as it should and my HR and power zones align (take that with a grain of salt I know).

So yea, let me know your thoughts on glucose efficiency improving or any research you know of that may be of interest. Thank you!

Eating higher quality foods while base training in your case is probably doing wonders for your glucose efficiency.

Have you tried any fasted rides? Something that helped me was to experiment with my body and go for a fast every once in a while (not fasted for any hard workouts). A big one was that I felt like it reset my mental perception of hunger and there’s a bunch of research that going without food every once in a while may have big biological benefits. Best to experiment with a fast when you don’t have a workout or, at least, a not very intense workout scheduled.

I guess the other thing to consider is to match the type of carbs you’re consuming to the activity you’re going to undertake. If you’re going for an easy cruise type of ride, slamming down a bunch of gels or “quick” sugar is probably a bad idea.

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I’m not sure if it’s specifically “glucose efficiency” or something else, but I’ve also found that fasted training has drastically changed my ability to ride long endurance rides with minimal fueling and not feel ravenous after. Took a while to work up the duration (from 30 minutes to ~2.5 hours) but I’ve found it helpful in both training and racing to not need such consistent fueling.

Definitely don’t recommend it for “quality” sessions (for me Sweet Spot and higher) as I find I’m too sluggish to hit my numbers well, but works great for endurance and recovery rides.


There is no question that glucose absorption can be trained. In fact, in much less time than than three weeks. Both digestive enzymes and GLUT-1/SGLT-1 will upregulate fairly aggressively if the focus of your exercise nutrition is primarily glucose. Like in a week or so. Of course, the same is true of GLUT-5/fructose.

For proof you need look no further than the various gastric emptying studies that are out there.

Just remember that gut training is specific. This is reflected in the race-day wisdom: don’t try new nutrition on race day. Train your gut to use the nutrition you intend to use.

Other things to remember! SGLT-1 is, as the name implies, salt (and ATP) dependent. To me, this is one of the most important reasons to keep a regular sodium intake throughout competition. Low sodium will impare gut glucose transport long before it will cause cramps.

Also remember that caffeine will improve SGLT-1 transport materially. Again, to me, this is the PRIMARY ergogenic benefit of caffeine during endurance exercise. CNS effects are tertiary (if that important) You may hear a lot of folks say ‘Oh, caffeine competes with GLUT-1 so it will act to slow glucose transport.’ There is some evidence to support this but GLUT-1 has such high Km anyhow that caffeine’s action to INCREASE STLT-1 activity far outweighs caffeine’s out-competing glucose for GLUT-1 transport.

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Interested in this and trying to understand it.

Do you mean that to if you train regularly with glucose supplements the body will use those more quickly or efficiently during racing or training? On the flip side what would that mean for those who train low/ race high in terms of fat/CHO consumption? In that case because the body is less used to dealing with glucose would it uses the glucose less efficiently?

Apologies if I’m misunderstanding but I’m trying get my head around the practical implications of glucose absorption training.

In the same vein as what @Brennus said, Asker Jeukendrup has an article on his blog about a study that suggests you can train your intestines to better absorb carbohydrates by giving it more carbs while training. See Includes links to open access articles in Sports Medicine for more detail.

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Interesting. I guess I have some reading to do. No need to be too skeptical but the research appears to be sponsored by PepsiCo/Gatorade. Going to have to dig through the references he uses to get to the bottom of this.

JulianM, I also find this topic quite interesting.

Yeah, for sure the gut will upregulate sglt-1 transporters in response to increased glucose in the gut. And quickly, too, within a week. Also for sure the profile of digestive enzymes in the gut will shift to accomodate an increased CHO load. And without a doubt timing CHO intake with exercise upregulates GLUT-4 in muscles…and probably GLUT-1 in blood but who knows for sure. So it’s a double-dip…increased absorption capacity and more efficient transport to and into muscles. More absorption, more efficient use.

But we haven’t figured out how to increase glucose absorption beyond about 1g/hr. That’s why GLUT-5 transport became such a topic of interest since that give another path to absorb additional CHO…in this case fructose. But, again, this is trainable.

Oh no! :wink: Don’t drag me into that crap storm! Ha!

No question, SGLT-1/GLUT-1/GLUT-5 can downregulate in the absence of Glucose/Fructose just like they can upregulate in the presence of Glucose/Fructose. So if you forego Glucose consumption in the weeks leading up to an event you will not be able to absorb or utilize glucose as efficiently on the day of the event. If you consider fructose as well we’re probably talking an 85 to 95 calorie per hour deficit.

But the question is, do you get even MORE advantage from training your body to use fat more efficiently? I think this question remains open ended! And it probably depends on the event.

I used to work on a daily basis with the guy who promoted the Rocky Racoon. He once told me in an ultra marathon it wasn’t a matter of if you did or did not run out of energy…it was just a matter of when you ran out of energy. So maybe he meant that in an ultra marathon everybody runs out of blood sugar eventually. In that case you’re probably better off being fat adapted. But in a 5k? No. In a 4hr road race? Probably not.

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I’ve no intention of going down the LCHF rabbit hole! I’m wary of any evangelists who know that their opinion is right :roll_eyes:

I eat what I think is a pretty normaI diet (certainly not low carb) but often tend to train on a empty stomach. For no particular reason other than habit often my first meal of the day will be lunch and that will be after a swim and a run or ride. As a general rule I start to introduce some nutrition if a session is over 2 hours whether running or riding and regardless of intensity so I guess that might lead to better fat utilisation over time.

My racing is focused on Ironman and my nutrition strategy tends to be pretty minimal compared to many people I’ve talked to about their race intake who seem to me to consume huge amounts of calories. Maybe that has helped over the years.

From reading your reply a strategy could be to introduce more glucose into or prior to training sessions in the weeks leading up to a race regardless if it is ‘needed’ for that specific session to promote glucose uptake. Losing the ability to process nearly 100 cals a hour would be huge in the context of IM (if I am understanding that properly)

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I think trying to adapt to carb intake is a moot point because you will reach your physiological max whether you optimize with glucose intake or not. The simple act of training and eating food, in general, will bring you up to levels that you can absorb maximally. More important is to include fructose, along with glucose when supplementing while riding because there are two different transport pathways and two separate pathways of deriving energy from those molecules. Other gains to be had by training with glucose intake is tolerability and that might be even more important than composition. Of course, these things are highly individual but we have to speak in generalities.

Training on an empty stomach in the morning without prior skeletal muscle glycogen depleting leads to liver glycogen depletion without muscle glycogen depletion. You will bonk due to depleted liver glycogen first and may miss out on whatever adaptations you try to achieve from a “train low” state. Protocols for total glycogen depletion require high intensity exercise muscle glycogen depletion the night before, no carb intake for 10-12 hours, then a fasted workout in the morning.

There was a study that showed a lack of evidence that going low carb training spares glycogen for race day for athletes that did ultra marathons (muscle biopsy tested). The evidence points more towards focusing on general adaptation through good training. If going low carb inhibits good training then it is a detriment. If on the other hand it helps, then by all means. This is highly individual.


I keep learning new things on here! :exploding_head:

Thank goodness I’m at the start of my fasted training block so I can stop working out my liver and start working my muscles instead.

So you can bonk while still having muscle glycogen available? Are you saying that the fat adaptations only occur in a ketotic state rather than simply being fasted?

Yup. The bonk feeling occurs when liver glycogen is depleted and not so much muscle glycogen depletion; although, you are often depleted of both when you bonk from long bouts of unsupplemented exercise. That’s because the brain, preferentially consumes glucose and the liver is the primary source of regulating blood glucose levels. Liver glycogen stores can be utilized to bolster blood glucose, which can then cross the blood brain barrier to bolster CSF glucose making for a happy brain. Muscle glycogen can’t be used to bump up blood glucose in this way.

Not really. I’m saying fat adaptations happen at all levels of training, especially proper polarized training like trainerroad. I think there’s a significant portion out there that believe they’re training in a lower carb state than they really are. It certainly appears that they’re feeling better in their training and racing. However, many may be falsely attributing it to depleting their muscle glycogen as the process to achieve that state is more involved.


I think I get that! Thanks for the explanation.