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How is it possible that the Red Bull Zero contains 0 gramms of fat, carbs and protein, but it still has 1.8 kcal of "energy". I always thought that the human body can gain energy only from 3 kinds of nutrients: fat, carbs and protein. Is there a 4th kind? Or they just display an energy value that's not accessible to the body?

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    $\begingroup$ This is slightly off-topic, since it's very unlikely to be related to your question - but yes, humans can gain energy from many more things than just sugar, fat and protein; it's just that those three are dominant in the food we eat. One example would be alcohol (ethanol); we can also process polyols and organic acids. Even fiber, which is often considered empty (and useful, mind) filler can be partially digested for about 2 kcal/g - so a single gram of fiber would be enough for that energy value (while being both a carbohydrate and a (poly)sacharide, it's usually listed separately). $\endgroup$ – Luaan Jul 18 at 8:13
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    $\begingroup$ @Luaan Exactly, I wanted to mention ethanol too. It was a big surprise to me and I actually had asked a question to find out how is it possible. $\endgroup$ – Tomáš Zato - Reinstate Monica Jul 18 at 15:19
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    $\begingroup$ @CrouchingKitten Nope. It does have carbon, oxygen and hydrogen atoms in the molecule, but that doesn't mean it's a carbohydrate, just like fats aren't. Especially in food context, "carbohydrate" essentially means "sugar", usually including some non-sweet saccharides like cellulose (in your photo, that would be in "Kohlenhydrate" but not under "davon Zucker"). Really, alcohol is closer to fats than carbohydrates, but even that isn't really all that useful. It's not commonly included in either group. $\endgroup$ – Luaan Jul 19 at 12:17
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    $\begingroup$ @CrouchingKitten The body does convert it to fats (if you're well fed), but I don't think there's any specifics dealing with the brain - after all, ethanol goes through the blood-brain barrier with no trouble. It has long been thought that ethanol doesn't cause the well known CNS symptoms on its own - it's the intermediate products of ethanol metabolism that do, probably mostly acetaldehyde. Assuming this is true, ethanol must be metabolised in the brain (and thus provide energy, as outlined in Tomáš's link), since acetaldehyde doesn't cross the blood-brain barrier. $\endgroup$ – Luaan Jul 19 at 13:15
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    $\begingroup$ @CrouchingKitten I doubt anyone would recommend it as a food source for the brain, unlike sugars and ketons, though; for obvious reasons :) $\endgroup$ – Luaan Jul 19 at 13:16
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The list of ingredients on the can mentions "Zuckerkulör," which is caramel colour, which can have 2 kcal/g, according to one producer.

Next, there is "Citronensäure," which is citric acid, which can, as other organic acids, have 2-3 kcal/g, according to this source.

There is also taurine, which is an amino acid-like compound, so it could, like proteins, have 4 kcal/g, but is, according to Taurine Metabolism in Man (Journal of Nutrition), poorly metabolized and probably has less than 0.2 kcal/g.

It is sometimes allowed, at least by U.S. Food and Drug Administration, to round the amounts of macronutrients (carbs, proteins, fats) smaller than 0.5 g per serving to zero, which is what they obviously did in this case, but they decided to keep the summary of calorie values of all ingredients exact.

It is usually said that only 3 types of nutrients contain energy: carbohydrates, proteins and fats.

Digestible carbohydrates (sugars and starch) provide 4 kcal/g. Undigestible, but fermentable, carbohydrates, such as soluble dietary fiber, sugar alcohols or polyols (maltitol, mannitol, sorbitol, xylitol, isomalt) and organic acids (citric, acetic acid, etc.), can provide 2 kcal/g of energy in average. On the other hand, some carbohydrates (such as "Sucralose" from the ingredient list) are neither digestible nor fermentable, so they do not provide any calories.

The "fourth" nutrient that can provide energy (7 kcal/g) is alcohol (ethanol), but is not considered a nutrient by some authors.

According to Food Label Accuracy of Common Snack Foods article (Obesity, 2014), the calories on the food labels should represent usable calories (metabolizable energy):

Of note, it is important to distinguish that food label calories actually represent metabolizable energy, which is total caloric content minus calories that are presumably not absorbed by the body and excreted as waste.

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    $\begingroup$ This article says that ~95% of ingested taurine is excreted. KEGG also says that taurine is not converted into any energy molecule in humans. $\endgroup$ – WYSIWYG Jul 17 at 17:54
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    $\begingroup$ Could it be Zuckerkulör (caramel colour)? It's just caramelized sugar. $\endgroup$ – AkselA Jul 17 at 19:59
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    $\begingroup$ This reminds me of a "zero calorie" recipe I once saw which involved ten squirts of cooking oil. Somebody had calculated the calorie count of one squirt, rounded to zero, and then multiplied that by ten... $\endgroup$ – Geoffrey Brent Jul 17 at 20:27
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    $\begingroup$ @AkselA There's very little caramel colour and, also, I'm not sure it has much energy in it: it's essentially already been partially burnt. $\endgroup$ – David Richerby Jul 17 at 20:50
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    $\begingroup$ @WYSIWYG, I checked that article and it really seems it is not taurine that provides calories. $\endgroup$ – Jan Jul 18 at 11:19

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