I thought I heard on one of the more recent peter attia podcasts that fructose reduces cellular ATP. I’m not entirely sure I got that right…and I’m not sure if they were talking about hepatocytes specifically or “cells in general” but…has anybody heard of this? Thanks,
Fructose is processed into glucose in the liver and in healthy individuals with ‘normal’ diets does not have any direct impact on muscle cells other than providing fuel substrate that can be turned into ATP. Its effects within the liver are certainly complicated and volume dependent but be careful with this specific body of knowledge coming out of Attia’s podcasts. He has presented some truly fantastic content but around this issue specifically he has lent his micorphone to some quacks.
OK so are you saying the fructose gets absorbed into the portal circulation, goes to the liver, and gets converted to 100% plain old glucose then put out into the peripheral blood? So the body only “sees” regular glucose and only the liver deals with fructose?
At least as far as the podcast goes, Richard Johnson, MD notes that the first enzyme in the metabolism of fructose (phosphofructokinase), is constitutive, that is it keeps causing the phosphorylation of fructose if there is any fructose around, and any high energy available phosphate; eg ATP, ADP, or AMP. The net result is free adenine that is metabolised to uric acid which promotes fat storage and inhibits mitochondrial function. The net result is an energy deficit in the cell, which signals the brain to consume more calories, leading to obesity, leptin resistance and metabolic syndrome. The uric acid also affects the kidneys, promoting hypertension.
On the other hand, Tim Podlogar a Research Fellow in Sports Nutrition at the University of Birmingham, in a podcast (I think it was Empirical Cycling), notes that as far as World Tour teams, fructose is essential, not only for getting up to 130 grams of carbohydrate/hr, and fructose seems to increase the rate of glycogen replenishment in recovery periods. I wrote Attia to try to clarify this, haven’t gotten a response.
You did hear that. However, if you are fueling rides in excess of 4 hours you should totally disregard this advice. It’s not incorrect but it’s totally out of context. For long rides, you will see a material net benefit by adding fructose to your fueling strategy.
And, it will make your villi longer.
It’s kind of in vogue right now to hate on fructose. We should all moderate our opinions on fructose compared to the twitter reactionaries. If you’re drinking 3 sodas a day, fructose is a problem. If you’re throwing a mango in your smoothie fructose is not a big deal. We would not exist as a species if fructose killed us or made us aerobically impotent.
If you’re riding hard for 5 hours, fructose is a solution, not a problem.
In the podcast, Dr. Johnson emphasized the production of uric acid as the main signaling mechanism for the harms attributed to fructose. This wasn’t discussed in detail, and I’m not interested in doing a deep dive into the literature. If I get around to it, I may read his latest book. It would be an interesting study to measure uric acid levels in endurance athletes that use fructose as part of their carbohydrate intake. Its clear that is probably best to stay away from sugar and high fructose corn syrup especially if not actively exercising.
If he responds please post it here, I’d love to read it
I hear you there, I don’t know what to believe most of the time. But for humans 10,000 years ago I would guess that fruit was scarce most of the year and they never really took in 1/2 pound of fructose over 4 hours like we (well…me?) sometimes do with 120 cal/hr of dextrose/table sugar (1/2 fructose/1/2 glucose).
I think it makes sense, just malto for rides under 4-ish hours. Not entirely sure I’ll do it though…but maybe?
totally makes sense
I don’t doubt this for a second but my question it kinda like calories from alcohol…you can get’em in but they aren’t really helping you.
Maybe. I’m old but I wasn’t around 10k years ago. Two words though: drunken monkey. The idea that fruit played a central role in our evolution is gaining traction these days. Or in that case, fermented fruit.
But I think you’re right on some level. I only eat nothing dextrose/fructose all day several times a year. Not every day.
I do for real encourage my opponents to eat something else though. Like avocado or macadamias or something like that. I’m concerned about their health.
I would have guessed that too but I was reminded of reading this memorable passage in Stephan Guyenet’s book The Hungry Brain. He’s referring to accounts by Western researchers of living with contemporary hunter gatherer populations
The gels are more expensive but seem to work better for me - I think my weight started creeping up from too much experimenting with high carb maltodextrin / fructose drink mixes for workouts when this wasn’t necessary.