Primal diet - Pros and Cons? page 24

[paleo-bunny]

Being a biochemisty graduate isn't proof of anything, no offense. The only tests that have been done on this have shown unrealistically high doses of pure fructose. Effects taper off as dosages are lowered. It's literally impossible to consume toxic amounts of fructose. It's like with anything else.

What's absent is the metabolic pathway.

Considering that fructose has been shown to protect the liver:

Fructose prevents hypoxic cell death in liver

To say that it's treated like a toxic is a fallacy

It seems you don't understand what a toxin is. It's the liver's job to metabolise toxins. Hence, any metabolite processed almost exclusively by the liver is de facto a toxin. No offense, but if you had a biochemistry degree, that would be trivial to you.

The gut protects the rest of the body from fructose by having a variable limited permeability to fructose. So often the gut takes the hit, rather than the liver.

As I said before, fructose is 100 times as oxidising as glucose.

Rat studies (as per your link) are irrelevant to humans.

[Derpamix]

It seems you don't understand what a toxin is. It's the liver's job to metabolise toxins. Hence, any metabolite processed almost exclusively by the liver is de facto a toxin. No offense, but if you had a biochemistry degree, that would be trivial to you.

The gut protects the rest of the body from fructose by having a variable limited permeability to fructose. So often the gut takes the hit, rather than the liver.

As I said before, fructose is 100 times as oxidising as glucose.

Rat studies (as per your link) are irrelevant to humans.

Liver has the highest capacity, but other organs do metabolize it and skeletal muscles can metabolize fructose via the Glut5 expression.

There is also this:
Metabolic effects of fructose and the worldwide ... [Physiol Rev. 2010] - PubMed - NCBI

They found that 50 percent ends up as glucose, 25 percent goes to lactate and greater than 15 percent goes to glycogen. The remainder is oxidized directly (to CO2 through the TCA cycle) and a small portion – as low as 2-3% – is converted to fat via de novo lipogenesis.

There is no evidence to suggest that fructose is a toxin, nor does your analogy of toxins hold up.

[paleo-bunny]

Liver has the highest capacity, but other organs do metabolize it and skeletal muscles can metabolize fructose via the Glut5 expression.

There is also this:
Metabolic effects of fructose and the worldwide ... [Physiol Rev. 2010] - PubMed - NCBI



There is no evidence to suggest that fructose is a toxin, nor does your analogy of toxins hold up.

It's not an analogy - it's a definition.

It does hold up. If fructose was such a great thing then our livers would perform fructoneogenesis. They don't.

Glucose is a way superior, healthier energy source, thus most people report much better energy levels and health from consuming safe starch over sugar.

[YogaBare]

When fructose goes to the liver, is it definitely to be metabolised? If 50 percent of metabolised fructose ends up as glucose, is it possible that fructose goes to the liver because the liver stores glucose (in the form of glycogen)?

Those are genuine questions. I have no idea! But initially I was so wowed by Lustig's video. I've since watched it probably 8 times, and the more I watch it the less sure of it I am. I don't trust Lustig. Why is he so angry? By and large, where there's anger, there's an agenda. Plus I work in media, and I have an innate distrust of sensationalism. I saw him interviewed in "The Men who made us fat" and he seems like a bit of a media whore.

I know that sounds like a stupid reason to discount something that seems well presented, but I'm sure Ancel Key's research looked great at the time too.

[YogaBare]

Anyway, that whole video is about fructose being a poison. Lustig himself says that "glucose is good carbohydrate. Glucose is the energy of life." Sugar is 50% fructose, 50% glucose. Shouldn't the video be called "Fructose - the bitter Truth"?

[paleo-bunny]

Unlike glucose, fructose enters the glycolytic pathway in the liver after the rate-determining step, hence most of it is metabolised down to pyruvate very quickly which can either be used for energy production in mitochondria or converted to fat. Very little is converted to glucose normally.

This is why excessive fructose tends to cause build up of fatty acids in the liver, especially in metabolic syndrome. There is nowhere else for it to go, as unlike glucose it is not taken up by muscles for future energy storage in the form of glycogen, nor is it readily converted to glycogen in the liver.

I agree YogaBare - the video should be called 'Fructose - the bitter truth'.

[SarahW]

Considering that fructose has been shown to protect the liver:

Fructose prevents hypoxic cell death in liver

To say that it's treated like a toxic is a fallacy

I think this study Long-Term Fructose Consumption Accelerates Glycation and Several Age-Related Variables in Male Rats is far more explanatory about the overall function of fructose than a study seeing what fructose does in the liver in the absence of oxygen.

I make sure to avoid hypoxia at all costs, so by also avoiding fructose I will also live longer. Simple.

[Zach]

Unlike glucose, fructose enters the glycolytic pathway in the liver after the rate-determining step, hence most of it is metabolised down to pyruvate very quickly which can either be used for energy production in mitochondria or converted to fat. Very little is converted to glucose normally.

This is why excessive fructose tends to cause build up of fatty acids in the liver, especially in metabolic syndrome. There is nowhere else for it to go, as unlike glucose it is not taken up by muscles for future energy storage in the form of glycogen, nor is it readily converted to glycogen in the liver.

I agree YogaBare - the video should be called 'Fructose - the bitter truth'.

"It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation." -wikipedia.

PB, do you think that keeping liver glyogen filled is a good thing or do you think all fructose should be avoided?

[Drumroll]

After a good workout you need muscle glycogen to be refilled, forget about liver stores. And even then, the need is not immediate to restore muscle glycogen unless you plan on going hard for round two right away. Heh.

Just make sure you've had a good meal before your next workout, whenever that is.

[Neckhammer]

...do you think that keeping liver glyogen filled is a good thing or do you think all fructose should be avoided?

I'm sure she will answer, but I have a question....why do you believe its an either or question? Are there no other sources for refilling liver glycogen besides fructose?