Sense 1: fuel supply, provide, render, furnish Sense 2: fuel, fire supply, provide, render, furnish Sense 3: fuel take in, take up Sense 4: fuel stimulate, shake, shake up, excite, stir http://www.synonym.com/synonyms/fuel/

So called healthy drinks, means that, although they are called "healthy" in reality they are not because they are full of something which is very fattening. This fattening additive is adding to the problem of people getting fatter, not healthier. Used in this way, it means that the drinks are adding to the problem/crisis, for example, if you throw wood onto a fire that is already out of control, you are adding fuel to it, you are making it worse. I hope it makes sense, Clair