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Refined sugar is regularly described as the root of all evil, while sugar in fruit juice slips under the net.

I just noticed my 330ml juice has 33g of sugar in it.

There are currently initiatives across the US to ban sugary treats and sodas, which often have less sugar than fruit juice.

The ban would apply to any beverage that contains more than 10 calories per 8 ounces, except for milk products, milk substitutes like soy milk and rice milk, and fruit juices without added sugar.

Is there anything special about fruit juice that makes it's sugar less likely to cause obesity?

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Moz
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  • @Russell Steen thank you I could not find sources! – Moz Mar 24 '11 at 17:44
  • I think the sources were Robert. – Russell Steen Mar 24 '11 at 17:48
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    This isn't a complete answer, so I'll leave it as a comment. The AAP recommends not giving babies under 6 months juice, and instead use water. This is partly because they can cause stomach problems, but also because it can cause weight problems due to the high calorie content. [HealthyChildren.org](http://goo.gl/vhlBG) – Ustice Mar 24 '11 at 18:08

1 Answers1

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The human body can make use of refined sugar more efficiently than fruit sugar, therefore it provides more energy per unit and is more likely to cause weight gain (in theory). This answer is based on several assumptions, outlined below.

There are many different types of sugar. There are single sugar molecules (monosaccharides), such as glucose, fructose ("fruit sugar") and galactose. There are sugars composed of two or more single sugar molecules bonded together, such as sucrose (glucose+fructose), or lactose (glucose+galactose). Sucrose is basically table sugar, that you might put in your coffee.

"Refined sugar" normally refers to sucrose or to high-fructose corn syrup (HFCS), which is processed sugar composed of about half fructose, half glucose, plus some other stuff (the composition varies, depending on desired sweetness etc). The sugar found in most processed foods, soda and candy is mostly sucrose or HFCS (depending on what country you're in). Some research has suggested that HFCS can prompt greater weight gain than a similar amount of sucrose, for reasons not really understood well.

The sugar found in fruit is sometimes (depending on the fruit) much higher in fructose than glucose; for example, the sugar composition of apples juices in this study was 9.30-32.2 g/l glucose, 66.1-96.0 g/l fructose, 8.5-55.10 g/l sucrose.

Hugely simplified: the single sugar molecules are one of the main energy sources in our bodies (they gets oxidised into carbon dioxide and water, yielding energy). Pretty much all the other kinds of carbohydrates (such as more-complex sugars and starches) get broken down into simple sugars before being used in the body.

The answer stated above assumes that "sugar in fruit juice" is a greater percentage fructose than glucose, and that "refined sugar" is HFCS or sucrose. Glucose can be metabolized and used in any of the body's cells, whereas fructose has to undergo an intermediate metabolic pathway that only happens in the liver (where the enzymes required are produced). Thus, the metabolic pathway for the body to consume and use fructose is more complex and "expensive" than to use glucose. In effect, the body gets less bang for its buck from fructose than from a similar amount of glucose.

In conclusion, the body can make more efficient use of a given amount of glucose than fructose, therefore it is more likely to result in weight gain (in theory, and for sustained consumption over time). In practice, any difference in weight gain from fruit juice compared to (for example) soda is more likely due to differences in total sugar concentration for a given volume.

Note that excess fructose consumption can also produce its own negative health impacts, such as diarrhea.

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ropable
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    Truth be told, the sugar found in soad and candy is mostly HFCS, which is almost molecularly identical to fructose. It certainly isn't mostly dextrose or glucose as those are expensive and typically used in pharmacological substances or dietary aids. – iivel Mar 26 '11 at 02:24
  • What about things like "throwback" Pepsi or "Mexican Coke" (sorry if I get that name wrong, I'm not a regular consumer of it) that are supposedly made with "real sugar". (They are extra tasty!) – Adam Tuttle Mar 26 '11 at 03:33
  • @iivel: you're quite right, my answer was written with a couple of unstated assumptions. I will edit to make it clearer (also to find some citations). – ropable Mar 27 '11 at 07:13
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    While you're looking for citations, would you mind addressing the effects of natural fiber, etc. that usually come along with fruit sugars? From what I understand they keep blood sugar from spiking, thus preventing the release of too much insulin which triggers fat storage. –  Mar 28 '11 at 21:06
  • Your paragraph about the metabolic pathways needs some sources. Also if fructose does require more processing than glucose that doesn't necessarily mean less net energy is produced -- perhaps the longer process results in more ATP per molecule? Etc. – Matthew Read Dec 18 '12 at 20:43
  • "*more efficient use of … glucose than fructose, therefore it is more likely to result in weight gain*". Except for fructose, *all* carbohydrates get converted into glucose (dextrose), either by enzymes or the liver. The problem with fructose is that it *doesn't* get converted to glucose, but into lipids, which will turn into glucose only when the blood levels of glucose are low, or stored as fat when levels of lipids are too high. That's okay with a mix of types (makes energy last longer). The real problem is that fructose doesn't reduce hunger, so one eats more and the lipids store as fat. – Ray Butterworth Aug 20 '22 at 13:26
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    To be honest, this answer was written with only a very limited understanding of the metabolic pathway(s) involved. I'm not at all confident that it is valid, and probably needs to be withdrawn (or at least have some additional large caveats added). – ropable Sep 02 '22 at 01:40