Why just ONE?

Diet Pepsi is labelled, and has been marketed, as no-calorie since its introduction in 1964. Originally, it was sweetened by saccharin, but the formula was changed in the 1980s to use aspartame in order to avoid the metallic aftertaste often associated with saccharin. Aspartame is still the principal sweetener of Diet Pepsi, though now supplemented by acesulfame potassium. If you pick up a can of Diet Pepsi, and look at the nutritional information on the back, it will read zero calories, due to its total lack of sugar, in contrast to ordinary Pepsi, which is usually sweetened by corn syrup (or cane sugar, depending on the region). Of course, the lack of calories is the selling point for any diet soda like Diet Pepsi, and for a diet beverage, you really can't beat that - zero calories, I mean. There's nowhere else to go, no further reduction in food energy that can be made. Pepsi completely removed the sugar, and wouldn't you know it, the result was a no-calorie drink. Problem solved. Diet achieved.

But in 1998, Pepsi launched a new diet soda under the style of Pepsi ONE (rather obnoxiously spelled with all caps so that it's impossible to type the name without looking like a jackass). Pepsi ONE, which is, of course, still sold today, and quite popular, is an artificially sweetened version of Pepsi's flagship cola, much like Diet Pepsi. I often have wondered why it exists - the launch of another, parallel diet cola brand in the Pepsi pantheon seems intuitively counterproductive for Pepsi. Wouldn't they simply compete with one another? Is there a difference, and what is it? Just what is the deal with Pepsi ONE?

Pepsi ONE had a somewhat different marketing campaign when it was introduced - it was still, essentially, billed as a diet beverage, but the big marketing gimmick was that it contained not zero calories, but one calorie. Just one. Just an itty bitty one. Which is great, so far as a diet beverage is concerned - one calorie is nothing when a typical adult can consume about two thousand in a day. And one might go on to think that this was an achievement, to remove all the calories from Pepsi but for that last, stubborn single calorie - except, wait a minute, how many calories are in Diet Pepsi again? Oh yeah, none. Since 1964.

So what's the deal? What is that last calorie, and why is it there? Why couldn't Pepsi figure out how to get rid of the last calorie - or, is it even there? It's obviously part of a marketing gimmick - Pepsi ONE isn't a bad name for a drink, and the whole one calorie thing makes it a memorable product with an interesting quirky fact. How many other products have exactly one calorie, right? So is it just a lie, or is there actually, legitimately, one calorie in Pepsi ONE?

Right away, there are a couple things to say about this. Firstly, a lot of supposedly non-caloric sweeteners actually do have caloric value, but are just so much sweeter than sugar that they need to be used in vanishingly small quantities, rendering their caloric contribution essentially negligible. To use the example mentioned above, the sweetener of Diet Pepsi, aspartame, is a modified dipeptide. That means it contains two amino acids joined by a peptide bond, the same kind of chemical arrangement that makes up protein. These amino acids can be broken down and some energy utilized from them, and aspartame consequently does have a small amount of food energy in it. This brings us to the second point - a food labelled as zero-calorie doesn't necessarily have zero calories. Because Diet Pepsi contains aspartame, it must have some caloric value. However, as per the FDA regulations outlined in 21 CFR 101.60, any food which contains fewer than five calories per serving may be labelled instead as zero calories, at the discretion of the manufacturer. In other words, those last five calories don't count. So even though we know that chemically Diet Pepsi must have calories, it's okay to label it with zero because it certainly has less than five, and the FDA allows that kind of labelling.

But what about Pepsi ONE? The main difference between Diet Pepsi and Pepsi ONE is the choice of artificial sweetener. While Diet Pepsi uses aspartame with a small quantity of acesulfame potassium, Pepsi ONE uses about a 3:2 blend of sucralose and acesulfame potassium. Sucralose, often marketed under the trade name Splenda (which is not, incidentally, pure sucralose), is a chlorinated sucrose derivative that's about 600 to 1000 times as sweet as sucrose. These chlorine atoms give rise to some hydrophobicity in sucralose that enhances the molecules' ability to adsorb to the surface of taste receptors on the tongue, which is why it's so intensely sweet compared to the principally hydrophilic sucrose. Furthermore, while aspartame can be partially metabolized and yields some small amount of food energy, the scientific evidence gathered on sucralose indicates that the vast majority of it is just excreted completely unchanged within a day or so. The same is true of acesulfame potassium, so it would appear, in fact, that Pepsi ONE likely has less caloric content even than Diet Pepsi, despite the marketing to the contrary. There is nothing at all in the scientific literature concerning acesulfame potassium or sucralose to indicate that Pepsi ONE could possibly have even a single calorie.

So it's a lie! They're both lies, in fact - Diet Pepsi must have greater than zero calories, because it contains aspartame, which is partially metabolized, and Pepsi ONE must have zero calories, not the one calorie claimed in marketing. I find this very interesting in light of those FDA regulations I cited a bit earlier - they outline, quite explicitly, when you can effectively underreport the calories in your product with the label "calorie free" or "zero calorie", but there don't seem to be any rules at all about overreporting the caloric content of your product. I suppose because it was never really a problem - there aren't many situations in which high calorie is a selling point for a food item, so the FDA never had to deal with the situation. It could be that Pepsi took notice of this, and just outright lied about the caloric content of Pepsi ONE because, well, they legally can. There's no rule saying they can't!

As for the reason behind Pepsi ONE's existence, it seems to be a simple matter of taste - aspartame and sucralose don't taste the same, and most people seem to judge sucralose as more accurately approximating the flavor of actual sugar, probably because its molecular structure is very similar. I certainly agree with that assessment - of all artificial sweeteners I've ever tried, sucralose is the least loathsome. And Diet Pepsi? Well, it sticks around because it's just been around - a lot of people have gotten used to the flavor, and actually prefer the flavor of aspartame to that of other sweeteners, even sugar. Pepsi ONE was an effort to get more people on board the diet soda bandwagon by introducing a diet soda with a noticeably non-diet soda flavor profile - and it worked. Pepsi ONE is a very lucrative product, and it hasn't significantly reduced the appeal of Diet Pepsi.

Incidentally, I don't drink either of these sodas. I don't really drink soda very much anyway, and if I do, I don't care for diet. But out of curiosity, I did a quick back-of-the-envelope calculation to determine how many calories actually are in Diet Pepsi.

Ironically, for a twelve-ounce can - about one calorie.