The latest available data suggest that the current average consumption of trans fats is about one gram per day (according to the FDA, as reported by CNN last month). Given that experts on nutrition recommend we get no more than 1% of our daily caloric intake from trans fat, it appears the average American is already well below that. (A gram of fat yields about 9 calories, so that would be 1% of a 900 calorie diet, far less than what most people must consume to meet their needs for energy from food calories.)
So it would seem the elimination of trans fats is unlikely to make much difference in the public health, because consumption will change little. Certain foods that we still eat, though, contain notable amounts of these substances, and so if your diet includes significant numbers of, say, doughnuts, your trans fat intake might be a good bit higher than average.
Let's back up a little to look at how trans fats became part of our diet.
Several decades back the experts told us animal fat was bad for our health. And we responded by switching to vegetable oils. So the first thing to understand is the difference between a fat and an oil. In simplest terms, these substances are all built on molecules that are esters of glycerol (glycerides). If such a substance is liquid at room temperature, we call it an oil; if it's solid, we call it a fat. In nature, most of the glyceride-based substances from animals are fats, while most from vegetables are oils. There are well known exceptions. Coconut oil, for example, is solid at room temperature but liquifies slightly above that.
On the molecular level when you look at the bonding of carbon atoms to each other and to hydrogen atoms in the hydrocarbon chain that is the backbone of a glyceride, oils have fewer hydrogen atoms. The electrons that are part of the carbon atom, instead of participating in bonds with hydrogen atoms, form double bonds between the carbon atoms.
If we take an oil, which has fewer hydrogen atoms, and add some, we get a hydrogenated oil, which then behaves more like a fat (solid at room temperature). This is called a "partially hydrogenated oil," and you've probably seen phrases like that in the lists of ingredients on packages of food. In nature, the hydrogen atoms tend to be on the same side of the carbon chain, a configuration called "cis" in organic chemistry. When we add hydrogen atoms artificially, they tend to go on opposite sides of the chain, and chemists call that "trans." There is very little "trans" in naturally occurring animal fat.
So is trans fat bad for us because it's different from naturally occurring cis fat?
We used to think just the opposite. Those of us who are old enough to remember when margarine was first introduced will recall that it was thought to be much better for our health than butter. Margarine (partially hydrogenated vegetable oil) is trans fat. Butter is naturally occurring animal (cis) fat.
As the decades passed, there was intriguing evidence from population studies that trans fats might actually be worse than cis fats. They seemed to be associated with an increased incidence of colon cancer. And while we thought margarine was more "heart healthy" than butter, trans fats seem to be associated with worse, rather than better, findings when we have our blood tested for lipids. Specifically, trans fats are associated with higher levels of low-density lipoprotein (LDL) - the so-called "bad cholesterol."
My regular readers know that I am fascinated by the notion of truth in science. As knowledge advances, we are convinced that we are getting inexorably closer to the truth. We believe that what we "know" now is always more likely to be the truth, or closer to the truth, than what we "knew" before. We believe we are steadily getting better at discovering scientific truth, that our scientific methods are constantly bringing us closer to a complete and accurate understanding of scientific phenomena, including anything having to do with the life sciences - and therefore with health and nutrition.
We may be right about this. I'd certainly like to think so. But I believe it is important to bear in mind that evidence isn't better just because it's newer. Any time we have new evidence, we should regard it with a certain level of skepticism - not because we are clinging to our "old" truths, but because evidence should always be examined closely, and its quality and meaning judged carefully.
So let's imagine how we might go about answering the question of whether trans fats are bad. We'd start with a very large number of people willing to be assigned at random to any of several groups whose consumption of trans fats would be carefully controlled over a period of many years. We'd assign them to getting, say, 1%, 3%, 5% (and so on) of their daily caloric consumption from trans fats. And then we'd follow them for two or three decades, closely monitoring health outcomes we think might be affected by consumption of trans fats.
As you might surmise, no one has done a study like that. Instead, we have epidemiologic evidence. We ask people to tell us about their dietary habits, we hope that their recall and reporting are correct, and we compare them with other people whose diets (as they recall and report them) are different but who are otherwise similar in ways we think might influence their health.
As you likely realize, the second kind of study is much easier to do, but it is highly vulnerable to what scientists call "confounding." Many other factors, dietary and otherwise, may affect people's health, and trying to identify them all and make adjustments in our statistical analysis, is tremendously challenging.
Thus a study done prospectively, in which the use of large numbers of subjects and the process of randomization minimize confounders, is much more reliable. We still have the question of whether subjects will do what they're told, but we can ask them to keep an accurate diary and see for ourselves whether they followed instructions. A diary maintained contemporaneously tends to be much more reliable than recall and self-reporting.
Trans fats are bad. That is the message people have been hearing for quite a while now. And some laws have already been enacted. Restaurants have been prohibited from using trans fats in New York City, for example. Thus our consumption of trans fats has already declined very substantially.
So we can predict that, if the FDA declares that trans fats are no longer "generally recognized as safe" and prohibits their use in commercially prepared foods, the impact on the public health may be modest at best. Might it affect an individual who eats a lot of doughnuts much more? Maybe.
Doughnuts and some other baked goods are made with trans fats to give them a lighter texture. Without trans fats, doughnuts would likely seem more oily. Partially hydrogenated oils stay in the "matrix" of the food and do not exude out of it. If doughnuts wind up being greasier because of a new FDA regulation, some people won't like it. I suspect the folks who make doughnuts will figure out a way to solve that problem, but I'm no food chemist, so I really don't know.
Let us keep in mind what we're talking about here. This is a proposed government regulation that would say, "Thou shalt not" use trans fats - unless you can convince the FDA that doughnuts made with trans fats really are safe.
What level of evidence should we expect for such an edict? There are some things for which we very reasonably believe we don't need evidence from a prospective, randomized, controlled trial. No one would seriously suggest, to offer my favorite example, that we need to do a study to find out whether it really is safer to jump out of an airplane with a parachute than without one.
When it comes to public health and the use of case control studies to try to figure something out, however, there are so many sources of error, bias, and confounding, that I have to wonder whether what we "know" today is clearly much closer to the truth than what we "knew" when the food scientists first created margarine to save us from animal fat. Just a quick review of the dizzying array of opinions on whether polyunsaturated versus monounsaturated vegetable oils are best for us will give you an idea of how challenging it is to be certain about things in this realm.
I don't have a problem with the government telling us what is good for us or outlawing what it thinks is bad for us.
Ha! I probably caught at least a few of you not paying close attention, reading that sentence and thinking I really meant that. The fact is, I do have a problem with that, especially when the evidence for what is good or bad for us is somewhat less than compelling. And this, I believe, is an instance in which it is quite reasonable to doubt the evidence and to ask whether what we "know" today is scientific truth.
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