Food has gotten so complicated, hasn't it?  Things used to be relatively simple.  Butter was the real thing; margarine was its cheaper, unhealthier cousin.  Margarine spread well, and cost a fraction of what butter did, but it was pretty obvious that neither were much good for you.

(One thing has remained true: never cook with margarine.  Any recipe which specifies margarine should be ruled out immediately.  I refuse to budge on this point.)

Back in the day, margarines were full of trans fats that would kill you, while butter had saturated fats and cholesterol that would kill you. Now it seems that the cholesterol content of foods is largely irrelevant to your blood cholesterol levels, but the fat content of butter puts it firmly in the "use as little as humanly possible" category from a health and weight perspective.

Margarine, on the other hand, has really cleaned up its act.  I bought a tub of Smart Balance margarine at the store last week, and was not only impressed by its claims, but baffled at how high tech it was.  If the tub proclaimed that "Smart Balance margarine is a valuable part of the Mars Rover mission," I would not have been surprised.

There are still a few margarines on the market which contain trans fats.  Be sure to check the ingredients list for the word "hydrogenated," because I have seen some which get weaselly with the nutritional information label.  The thing is, they are allowed to round their numbers.  So if a teaspoon of their margarine contains .90 grams of trans fats, they can still claim that it has "zero grams" of trans fat per teaspoon.  

In addition to being trans fat free, many margarines these days promise the moon, as far as I can tell.  The Smart Balance that I bought, for example, proclaims itself as having the "ideal blend of fats," and a good source of omega 3 fatty acids besides.  The only down side to Smart Balance is that it is a brick-like solid when you take it out of the fridge, and only begins to soften at room temperature.  I have learned to put a bit on my toast, then go do something else while the stuff softens up.  Curse you, non-hydrogenated fats!

This is an unfortunate constant with these new margarines, because the whole point of hydrogenated fats was to make things creamy.  Margarine or "buttery spread" manufacturers are having to get really creative with their ingredients, in order to provide a reasonable spreadability without hydrogenated oils.  Many spreads blend an unholy alliance of oils and butter together.  So if you were using margarine in order to get away from the fat content of butter, forget it!

Of course, ultimately one runs into the Michael Pollan dilemma.  The state of the margarine industry today is exactly the kind of thing that Pollan rails against (in his rational and ever so polite fashion).  Most of these spreads definitely qualify as being an "edible food-like substance," which Pollan warns against.