To Carb or not to Carb?

I was toward the end of a long endurance ride while eating the delicious malt balls courtesy of The Hut on Tunitas Creek in the San Francisco Bay area. I felt a little undisciplined since I had recently eaten an RX bar and thought I was eating too much, when I began hearing the podcast with Dr. San Millan.

I no longer felt guilty!

It used to be thought that around 60gs/hr was the upper end of absorption, then raised to around 90 g. The Insync testing uses 90g/hr as the top end of absorption and their FatMax graph has 90 gr/h as the top end.

Dr. Inigo Inigo San Millan, in the podcast number 205, brought a interesting perspective.

He noted not enough carb consumption as a problem. He said that for aerobic activities that they were finding that between up to 2.5g/minute
of carbs could be oxidized. That’s up to 150 grams per hour of carbs used in an aerobic ride. 600 calories.

Even in the classic fat-burning zone 1 of 3 aerobic rides where cyclists think that they are burning mostly fat and little carbs, he indicates that the carb expenditures could be up to around 400-500 grams for a ride. Close to 2,000 calories of carbs. And that athletes need to account for that or they could end up with glycogen deficit and start using muscle for fuel. That their stored glycogen stores may not be enough.

He did not say what the max ingestion was, whether he had new information on this, or what he does with his pro athletes, other than on higher energy expenditure days, the nutritionist had them eating more.

I wonder what you insights are on this…and on malt balls.

Other things that caught my attention: other biometrics that could be useful with some athletes is measuring insulin via C-Peptide ( about half of the insulin produced by the pancreas gets used by the liver within a few minutes, so the C-peptide test is more accurate). A lot of Type 2 diabetes and low insulin sensitivity has Liver insulin resistance as a significant factor.

Chronic insulin levels can act as a hormone disruptor, and can contribute to chronically elevated cortisol.

Another useful test is 24-hr salivary cortisol testing to see what the cortisol load and distribution is. Distribution issues may be coming upstream from the brain. Low cortisol load may indicated adrenal stress. Stress first elevates it, and over time for some, the levels start coming down.

This can affect catecholamines, since they are mostly produced in the adrenal medulla. I have seen that Ashwagandha and other adaptogenic herbs can be of help for adrenal function. Ounce for ounce, the greatest amount of Vit C is stored in the adrenals.

One other lab that was not mentioned, likely because of time, are Vitamin D levels. VO2 max, strength,endurance studies on this.

Digestive issues may cause low levels, even if supplements/adequate food is ingested. I’ve seen people on 1K international units a day for a long time still have low levels.

I lived and cycled in Miami and found I had low Vit D levels, so getting sun does not always mean the levels will be sufficient.

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Was San Milan talking about someone with an LT1 of 170W or 350W? I’m no expert but I’m pretty sure their fuelling requirements would be somewhat different.

Good point, he works with pro riders. He mentioned aerobic rides, I would not think that 350 Watts would be sustained on long training aerobic rides even with pros.

I’m nearer that 170W figure for LT1.

I did a 9 hour 59 minute hour ride yesterday of which 9 hours 10 minutes was pedalling time. Because it was out in England’s fens there was no coasting, constant pedalling.

The fens yesterday , where no one hears you scream :scream:

Here’s my heart rate zones for that ride

I had a 50g solution of Maltodextrin in my 750mL bottles, which works out at a 6.6% solution. I could barely taste it, if I can taste something in my water, I won’t tolerate for these length or longer rides. I drank 6 litres of this solution which comes up at 400g of carbohydrate. I’ve then added in breakfast and anything I ate in the ride to come up at 2,800 calories consumed from breakfast till end of ride.

I’ve read a research paper somewhere that once stored glycogen in the muscle gets below about 10% (of rested levels) that’s where you see muscle dysfunction etc. I don’t know the levels but I can concur that if I underfuel on these length rides then my legs suffer such issues after many hours of pedalling.

I suffered no such issues yesterday and no muscle soreness today.

I can only conclude that 2,800 calories is sufficient intake for me for a ride of 9 hours at my current capabilities. What I can say though is that much of my stopped time was needing to pee. If I’m to get most of my calories from Maltodextrin on these rides, then I’ll have to see if I can tolerate a more concentrated solution. Otherwise it’s more stops to eat solid food, or more food with same number of stops.

Of course what we don’t know is how good my fat oxidation is at the effort levels I’m pedalling.

I think for carbohydrate intake on long endurance rides it’s a case of a n=1 experiment to find what works for you. If you pay attention to your RPE and HR during the ride, and note your intake, how you felt throughout, how you felt at the end, and how you feel next day. Then you’re well on the way to working out what works for you.

Do you have any numbers for KJ’s on the ride from your power meter. That’s some ride with the constant pedalling. I may be wrong but the peeing could be due to your glycogen stores reducing with the commensurate reduction in body fluid and maybe if you didn’t have enough electrolytes your body wants to get rid of fluid to keep your salt concentration correct. ( I may be wrong about that though).

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Don’t have a power meter outdoors. But even if you do it doesn’t tell you the internal energy needs just the external. You’re then fudging a guess at how efficient you were at turning calories to power through the pedals etc. software zone breakdown?

Yes it is. It had me down for a 3 hour endurance ride and for some reason I couldn’t get my brevet event in the planner. Thus it has me as compliance above planned. However the ai isn’t reflecting the fatigue generated from 9 hours 10 mins for riding even if mostly Z2. Paul agrees and they are looking into it. In a way the long brevet events I do will be a good test for it.

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Maybe Dr. Inigo could have been talking in the podcast about the need for more calories based on some of the research that this article mentions. The takeaway from the article is that you need more calories than you may think for endurance rides, and that the carb loading should begin around 36 to 48 hours before the endurance event.

In my experience. There is no such thing as eating to much on the bike. As long as you don’t upset your stomach, eat it all i’d say. And i can hear the riders screaming, “but you mostly use fat in Z1/Z2”. Yeah, but you’re still burning the calories. More eating on the bike will make those 5+ hours rides feel “easy” and after the ride you don’t feel the need to eat everything in sight.


Yep, when I ingest more carbs than the science says, I feel better in the long rides.