A February 25, 2007 piece by Jonathan Last notes ACSH's opposition to trans fat bans:
For starters, as the American Council on Science and Health notes, as a result of bans like this, "the risk to heart health from [trans fat] is likely to decrease...but we do not know that the fats that will replace [them]...(quite possibly some form of saturated fats) will be any less detrimental -- and this is the problem with overzealous rules to ban [them] outright." And since trans fats and all other fats have the same number of calories per gram, removal of the former "will not necessarily result in lower calorie consumption -- which is what is needed to deal with the soaring prevalence of obesity in the United States."
For essentially those reasons, the American Heart Association opposed a similar ban in New York City last year.
See also: ACSH's full report on Trans Fatty Acids and Heart Disease.