"Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients"
"The results of the taste tests were strong — the sweeter mixture overwhelmingly beat both regular Coke and Pepsi. Then tasters were asked if they would buy and drink it if it were Coca-Cola. Most said yes, they would, although it would take some getting used to. A small minority, about 10-12%, felt angry and alienated at the very thought, saying that they might stop drinking Coke altogether. Their presence in focus groups tended to skew results in a more negative direction as they exerted indirect peer pressure on other participants."
So basically, diet coke's formula is essentially new coke, which tasters seemed to generally like better than regular coke.
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There is no shame in not knowing; the shame lies in not finding out