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As I understand it, the process you describe is true of glucose but actually not fructose. Glucose gets absorbed into your blood, causes your pancreas to start releasing more insulin into the blood, which causes basically all the cells in your body to start absorbing glucose.

Fructose on the other hand can only be processed by your liver, so all the fructose you eat just kind of queues up for your liver to process it. It doesn't cause you to release insulin so it has a low glycemic index. Your liver can convert fructose to glycogen and then to glucose to feed your cells if you don't eat any carbs or glucose. But if you already have more than enough carbs/glucose, your liver instead converts the fructose to fat and stores it. This can lead to fatty liver and somewhat interestingly can also lead to insulin resistance which then makes you worse at processing glucose. Alcohol also gets processed exclusively in your liver and can cause fatty liver, so it is true that juice and beer can do a similar kind of damage.

Anyway, on the bigger point I 100% agree that juice is bad for you. It's sad to see it so often touted as healthy.

EDIT: One thing I do wonder about, people always point to fiber as a reason why fruit is ok but fruit juice isn't. It seems like it would be a lot easier to get people to start taking fiber supplements than to stop eating sugar, so why don't we ever hear that advice?

Fructose on the other hand can only be processed by your liver

You're correct and my original post is incorrect with regards to fructose. Thanks for pointing this out - it's better to be wrong but enlightened.

And that makes you're both right now!

Lustig goes through all the processes here:

  https://www.youtube.com/watch?v=dBnniua6-oM

But the sugars in fruit are not all fructose, right? It's a mixture of a bunch of different kinds of sugar molecules. I'm not sure what the exact ratio is, afaik in apple and orange juice the sugars are at least 50% glucose--but I'm not sure where I read that and it might be way off.

Either way, apple juice and orange juice have about 10-12g carbs per 100g (according to the packaging, in NL). Coca Cola has (not sure) I think, about 11g/100g? So I treat it about the same and drink it rarely.

The only difference is, you can mix up most types of juice 50/50 with tap water and it'll taste good (and if you're thirsty, actually better IMO). Try that with Coca Cola and ... nope :)

I've never understood the glycemic index stuff. It didn't seem to fit my experience. I just researched this, and I came upon this article: http://www.foodrenegade.com/glycemic-index-vs-glycemic-load/

I had never heard of glycemic load before today, and I'm always reading articles about nutrition science. It seems like fruit and veg have relatively high glycemic indices, but low glycemic load--which means that they're fine, which makes sense. Who here can imagine a doctor telling anyone on earth not to eat more carrots?

EDIT: I also found this article: http://www.calorieking.com/learnabouts/The-Glycemic-Index-Th... which had this quote: The glycemic load (GL) goes a step further than the GI by taking into account the amount of carbohydrate in a food. A weak point of the GI is that it fails to do this.

For example, carrots have a high GI of 47, but you have to eat a pound and a half of them for there to be a steep rise in blood sugar.

This completely meshes with my experience.

> Who here can imagine a doctor telling anyone on earth not to eat more carrots?

Completely tangential, but I can imagine doctors treating patients complaining of Carotenosis:

Carotenemia or carotenaemia (xanthaemia) is the presence of the orange pigment carotene in blood from excessive intake of carrots or other vegetables containing the pigment resulting in increased serum carotenoids. - https://en.wikipedia.org/wiki/Carotenosis

For example, carrots have a high GI of 47, but you have to eat a pound and a half of them for there to be a steep rise in blood sugar.

carrots are full of water, not to mention roughage, so they don't have high caloric density per unit mass/weight

the glycemic load is precisely articulating the index number adjusted per unit mass to account for stuff like caroots or beets etc.

So basically if you ate de-hydrated fruit or vegetables that will load higher (per unit mass) than stuff full of water...because whater has no cals...so water and starch dilute glycemic index

The glycemic load is calculated by multiplying the glycemic index of a food by the amount of carbs in a 10 gram portion of the food.

In practice, you can dilute glycemic index using fat and protein in addition to water.

> In practice, you can dilute glycemic index using fat and protein in addition to water.

And people really don't understand this. For instance, you basically can't find full-fat yogurt in an American grocery store. Instead there's 20 kinds of non-fat yogurt packed with sugar, which have a much higher glycemic load than yogurt with the same amount of sugar and fat would. But they're all advertised as being healthy because they're non-fat. It's crazy.

> If you plot the blood sugar concentration of the person consuming a solid piece of fruit you see a nice curve where the levels rise, peak, and non-violently fall.

There's nothing wrong with this except that it probably makes you feel more hungry and eat more. But the blood sugar surge isn't really unhealthy in normal people, it's usually the subsequent behavioral impact (the low that makes you feel hungry) that causes the real harm (ie: the total sugar matters more directly than the glycemic index).

There's nothing wrong with this

I agree there's nothing wrong with the part quoted. That's an ideal outcome. And the surge of blood sugar concentration from juice wasn't the part I was concerned about (unless it results in a child going into a hyperactive transdimensional shit-fit). The blood sugar crash is the significant part: https://en.wikipedia.org/wiki/Hypoglycemia#Signs_and_symptom...

Low blood sugar also plays a major part in decision fatigue. Do you make dinner after work or buy something on the way home? Making a healthy dinner is the better decision but right now you want satiety. Do you do the washing or sit in front of the TV? You don't just have decision fatigue, you're out of energy - the real deal.

This is in contrast to a low GI meal where the energy supply is provided over a longer period at a stable rate, providing the stamina to make good decisions and act on them.

Yep, totally agree with all this! Just pointing out that the low blood sugar in and of itself is probably not a huge deal from a health perspective, just the bad decision that comes from it.