Lipids (or fats)
Olestra : a fat that doesn't make you fat
This fat molecule shown below has a very unusual property: it doesn't make you fat! What is the tricky?
Olestra
Its well known that there are lots sugar substitutes on the market. This substances provide a sweet pleasure without making you fat. The trick, in this case, is that those substances mimic the sweet flavour and don't afford the Calories. In other words, they cheat your tongue. In fact, they are sometimes hundreds of times sweeter than sugar and that is why very small quantities are used.
Have you ever wondered why a similar substitute hasn't yet been found for fats? At the end of the day, fats are the most fattening foods consumed by people. Yes, such substitute exists, and its structure is shown below:
Surprisingly this strucutre is composed of fatty acids (as you can see). Each olestra fat molecules comprises 6 fatty acids, instead of only 3 like in the case of triglicerids (normal fat).
The trick in this case is a different one. The palative receptors in your tongue are not being cheated this time. What happens is that this fat molecule is too big to be absorbed in the intestines, so that it find its way out trough the anus. That means that you can experience the pleasure of eating fat without having it inside your system (and as a result making you fat)!
Unfortunately it causes a few side effects and that is why it hasn't been a great commercial success. However, it is still used in certain snacks and other fatty products.