Cooking with Your Brain: Lecture 2: Demystifying Your Ingredients

Part 1: Fat

These days, you nearly always have two options when you buy a food item: Original and fat free. It has become trendy to select fat-free options when possible since they're socially considered healthier. Interestingly, most people just sort of accept this without thinking about it. Do you really know what fat is? Do you think about what terms like fat-free, low-fat, trans-fat, or saturated fat actually mean when you buy those foods?

Figure 1. Fat Free Foods

All of those subtle variations make a big difference in how your foods look and in how your body handles them. To explain it all, we're going to have to dig a little bit into organic chemistry. But hopefully, after this, you'll have a better understanding of what you're really eating.

The Organic Chemistry of Carbon

First, we have to provide you with a little background on carbon for the rest to make sense. Brace yourself...

Figure 2. a) Methane, b) Formaldehyde, c) Carbon Dioxide,

d) Acetylene

Carbon atoms must be attached to exactly four other things to be happy and stable. They can satisfy this requirement in different ways. Overall, the number of bonds it makes with other atoms must equal four...and things get complicated because it can make single, double, or triple bonds. For instance, one carbon atom can single-bond to four different hydrogen atoms to make methane (Fig. 2a), it can single-bond to two hydrogen atoms and double-bond to a oxygen atom to make formaldehyde (Fig. 2b), it can double-bond with two oxygen atoms to make carbon dioxide (Fig. 2c), or it can triple bond with another carbon and single bond with one hydrogen to make acetylene (Fig. 2d). It can also forgo a bond for a pair of electrons, called a "lone pair" to keep for itself (replace the H's in Fig. 2d with two lone pairs and you've got carbon monoxide.) These are just some examples of what carbon can do. Carbon's versatility makes it the basis of all life.

Fatty Acids and Saturation of Carbons

Figure 3. a) Saturated Fatty Acid, b) Monounsaturated Fatty Acid

What does this have to do with fat? Well, fat is primarily made up of chains of carbon that have hydrogen atoms filling up the carbons' available spaces for bonding. Hydrogen is capable of making only one bond, which is why you see it single-bonding with carbon all over the place. If all of the carbons are bound together with single bonds, its called a saturated fat, because the chain is as full of hydrogen atoms as it can get (Figure 3a). If two of the carbon atoms are double bonded together, there suddenly isn't enough room for as many hydrogens because carbon will not make more than four bonds. These fats are called unsaturated fats, because some hydrogens were kicked out (Figure 3b). You can probably guess what polyunsaturated fats are (Hint: poly = "many" in Greek).

Two commonly used cooking materials are made of fat: Oil and butter. However, you may have noticed that oil is a liquid and butter is a solid. "But they're made of the same thing!" you say. How can that be? Butter is made of saturated fats, the ones with only single bonds. These fatty acids are straight as an arrow, and therefore can get really close together to form a solid. Oils, on the other hand, are made of unsaturated fats, the ones with the occasional double bond. Double bonds, in certain cases (see below), form a "kink" in the chain, in that they made the chain bend. These bent chains can't get as close to each other, therefore they don't stick together as well, and this results in liquid.

Cis vs. Trans Fats

You've probably heard of trans-fats. Well, that name comes from some organic chemistry nomenclature. Cis and trans are the names of the two ways hydrogen atoms arrange themselves around double-bonded carbons. To explain why hydrogen bonds arrange themselves the way they do gets a little complicated, so we won't get into that. Let's just say that due to some natural forces, trans bonds maintain that straight orientation for fatty acids, while cis bonds cause a kink to form (Fig. 4). Therefore, like explained previously, trans-fats can pack closer together than cis-fats. This means they can form plaques in your arteries, which is BAD FOR YOU. Trans-fats also increase levels of LDL (bad cholesterol). Therefore, you should avoid trans-fats!