Corn is a fruit… high fructose corn syrup is just syrup made from corn. It’s the most refined and insidious form of fructose, but not the only one.
Nature couples fructose with fiber and phytonutrients so you get some good with the bad. But when you remove all the good, you’re left with just the very very bad.
Fructose to fiber/micronutrients ratio varies a lot by fruit. Corn is probably the worst but berries and citrus are close to the best (of the worst) and there’s a spectrum between them.
Fructose does not have an insulin response… but fruit generally has both fructose and glucose sources that will spike insulin. That ratio varies by fruit.
This is because no organs can metabolize fructose except for the liver, so there’s no direct conversion to blood glucose, and no need for insulin. Insulin’s primary function is to sequester blood glucose since excess BG can cause damage to blood and brain cells… it’s protecting the body…
The liver is the master commander of metabolic processes, it pulls the fructose directly and captures it without the need for insulin. It is the only organ that can do this and it’s the one that takes the brunt of the damage with fatty liver disease.
So can I say?
fructose sweetners in small quantities should not be an issue.
for athletics people even moderate quantities should not be an issue.
One more point… fructose drives fatty liver… fatty liver drives insulin resistance… insulin resistance increases chronic insulin increase…
So unlike glucose that spikes insulin when consumed, fructose causes a chronic condition that promotes metabolic disease…
I think it should be avoided by diabetics and people with normal activity. Daily use may induce a somewhat fatty liver. There are better sugar replacements out there.
I do not think I need any fructose or other carb before gym. I mean I did try before gym but they just screw my hunger.
But this brings to me the question:
Carbing up and consuming all the carbs through intense sport is not quite bad… But I think it is not natural for the body to have this processes going on continually. Our ancestors were muscular without carbing and going to the gym.
I’ll say that fructose in excess that causes fatty liver will indirectly increase insulin…
On Keto, if you cycle fructose, it will deplete liver glycogen and fix fatty liver over time. As long as it’s only a reserve that is tapped into, it should be ok… if you accept that it’ll just delay your Keto progress.
Think of it as a fuel tank before getting into your fat reserves. If you overfill it, bad things happen. If you full and then deplete it, it just slows down your fat loss.
No. It directly causes insulin resistance. It is more potent in causing insulin resistance than even glucose. Fructose is pretty much as bad as it gets.
Here, healthy subjects were given 25% of their daily calories as Kool-Aid sweetened with either glucose or fructose for 8 weeks. While this seems like a high percentage, there are many people who consume this high proportion of sugar in their diets.
The oral glucose tolerance test is a standard test for diabetes and pre-diabetes. The blood sugar is measured in response to a sugary drink given to the patient. The fructose, but not the glucose group has already developed pre-diabetes . This is supported by the finding that the fructose group has developed significantly more insulin resistance than the glucose group.
https://idmprogram.com/fructose-causes-insulin-resistance-hormonal-obesity-xxxii/
Carbs for athletic performance isn’t necessary. This is especially true for endurance sports like marathons. However, some activities like sprinting do require explosive execution… in those cases, glycogen reserves do help improve performance.
As usual, it depends. I lift weights while fasted. Is it explosive? No… is it effective? Yes.
I increased my weight and runing with zero carbs.
When I take one of those energy bars I feel stress to run to deplete the carbs.
If you’re looking for muscle gains… focus on protein
Not carbs or fructose
Fructose was first discovered in fruit, hence the name, but forms one-half of a molecule of sucrose—table sugar—which is a glucose molecule and a fructose molecule bonded together. Fructose has a noticeably sweeter taste than glucose, and is responsible for much of the sweetness of table sugar.
Glucose in the bloodstream can be intensely damaging, so insulin is mobilized to drive it into the muscles for use and the fat tissue for storage. Every cell in the body can metabolize glucose.
Fructose can be metabolized only in the liver, and it is is dealt with by the same pathway as handles ethanol. This means that fructose in quantity—either too much over the long term, or more than the liver can handle in the short term—causes the same liver damage as ethyl alcohol. Fructose also affects the dopamine receptors in the brain in the same way as alcohol, and so it is just as addictive. It lacks only the short-term toxicity of alcohol.
Explosive performance is provided by glucose, not fructose, since the muscles cannot metabolize fructose, and glycogen cannot be shared between cells. Excessive glycogen in the liver is part of what makes the liver insulin-resistant, along with the fat droplets created by an excess of fructose in the liver. This means that fructose directly, not indirectly, causes insulin-resistance.
The glucose used in the muscles of a keto-adapted athlete for explosive performance was manufactured by the liver from dietary protein and shared as glucose. Liver glycogen (as I understand it, anyway) gets metabolized in the liver—once carbohydrate intake drops low enough to permit it.
The fructose in sucrose and the fructose in high-fructose corn syrup is the same molecule. I believe that the only difference between sucrose and HFCS is that the fructose and the glucose are not bonded together in HFCS, and of course the percentage of fructose is 55%, not 50%.
This lecture details the metabolism of fructose in the liver:
That’s right Paul.
However, for athletes who need explosive performance and want to replenish their glycogen, there is a limitation on glucose only conversion. There are different transport mechanisms for glucose and fructose and using both accelerates the total transport rate. The muscle glycogen is key, but in the case of athletes, replenishing liver glycogen is also important.
To be clear, this is very far away from most people. It’s not just athletes… this is for athletes who engage in explosive performance activities.
I am explicitly not advocating this. I train nearly every day while on extended multi-day fasts with intentionally depleted glycogen stores (both liver and muscle) and I don’t see this as applicable to me.
If you’re a sprinter, Olympic swimmer, MMA, cage fighter, or massive heavy lifter… this might apply.
Phinney and Volek have released a study showing that the glycogen stores of athletes who have been keto-adapted for long enough are indistinguishable from those of carb-fed athletes. It is true, however, that explosive performance suffers until the glycogen store normalizes.
Here is the full text of one of the studies Thomas cites. It does use cyclists but I think it’s still relevant. I think if one was to implement this, 15g/15g would be roughly the max.
Agreed that endurance athletes who are fat adapted actually have an advantage. That’s why I focused on explosive performance athletes.
As usual in life… it depends… 