I have always told my classes that they may ask questions at any time. I wanted to avoid waiting until the end of the lecture to ask, "Are there any questions?" Because if no questions came forth, there were two possible explanations: Either my lecture had been so brilliant that not the tiniest point remained unclear, or the students were so befuddled they didn't know what to ask. I didn't want to have to guess which.
So I didn't end my March 2 column on "fats for dummies" with the words, "Are there any questions?" -- not because I feared an absence of questioning e-mails. I knew my deliberately oversimplified treatment had left a lot of room for questions.
Here, then, is a follow-up primer on fats -- not for dummies, but to fill in some of the gaps. Before you get too conceited about your knowledge of fats, however, remember that we are all fatheads. About 60 percent of the dry weight of our brains is fat.
Are trans fats natural?
In the previous column, I stated that trans fatty acids (FAs) are rarely found in nature and that our metabolism is geared to handling the more natural kinds of FAs that chemists call cis (pronounced"sis").
This was not meant to imply that there are no trans FAs at all in nature (as is often stated), or that our metabolism can't handle small amounts of them. There are, and it can.
While most of our intake of trans FAs comes from manufactured food products containing partially hydrogenated oils, a small percentage of our trans FAs comes from relatively unprocessed foods such as milk, cheese and butter, a fact that you will never see in the dairy industry's advertising. (Got trans fat?)
So if we Homo sapiens have been eating natural trans FAs for hundreds of thousands of years, why all the fuss about them today? Several reasons: We just discovered how bad they are for us, and while we may not be able to do anything about the trans FAs in our milk, we can certainly do something about the trans FAs in our doughnuts. Also it is unclear whether all trans FAs are equally harmful.
First, how did those trans FAs get into our dairy products?
When cows and other ruminants such as sheep, goats, camels, rhinoceroses, llamas and giraffes eat vegetable matter, some of the unsaturated FAs in their diets become partially hydrogenated by bacteria in the animals' rumens -- the first and biggest of their several stomachs. And just as in factory-produced hydrogenation, bacterial hydrogenation produces trans FAs that wind up in the milk fat and cheese, the meat's fat, and, to a lesser extent, in the meat itself. Somewhere between 2 and 9 percent of the FAs in butter, for example, depending on its source, are trans FAs. (I could not find any data on cheese made from rhinoceros milk.)
How did our metabolism deal with these natural trans FAs before we began making them artificially in hydrogenation plants?
Our digestive enzymes can handle small amounts of trans FAs, but when larger amounts are digested and incorporated into our cell membranes, the membranes become distorted and don't function properly. So the problem is not so much trans FAs per se, but too much of them in our modern diets.
Are all trans fats equally bad?
There are trans FAs and trans FAs. They're not all the same.