Trans fats offer up an intriguing window into the evolving science of nutrition. In the 1980s, public pressure led many restaurants to stop using saturated fats such as beef tallow for deep frying and switch to partially hydrogenated vegetable oils. But over the years, it's emerged that these mostly manmade fats -- currently referred to as artificial trans fats -- are even more detrimental to heart health than what they replaced.

Unlike animal fats, which raise LDL ("bad") cholesterol, trans fats have double the whammy on blood lipids linked to heart disease. Trans fats not only raise LDL, they also lower HDL cholesterol, the good kind that scours out blood vessels. In addition, trans fats promote inflammation, also thought to play a key role in heart disease, as well as promote obesity and insulin resistance, a precursor to diabetes. Harvard researcher Dr. Walter Willett didn't mince words in an interview this week. "Think of this as arsenic. It's poison." And yet, artificial trans fats remain in the food supply -- mostly in deep-fried foods and commercially baked goods -- in large part because they don't spoil as quickly as other oils and they're often less expensive.

Although the food industry is making strides in removing trans fats, a national debate should have occurred long before now about the need for federal restrictions on this dangerous ingredient. Denmark has effectively banned trans fats, and a number of Western Hemisphere countries are pushing to restrict their use. But despite petitions from advocacy groups and studies from leading researchers, the U.S. Food and Drug Administration (FDA) continues to classify trans fats as "generally recognized as safe."

That has politicians across the nation considering local bans on artificial trans fats. (The word "artificial" is important here because small amounts of trans fats occur naturally in some foods.) New York, Boston and Philadelphia are some of the biggest cities that ban trans fats in restaurants. California is phasing out trans fats statewide in restaurants and commercially baked products. In the Twin Cities, Minneapolis and St. Paul city council members plan to pursue a ban on artificial trans fats in restaurant food served by big chains. Minneapolis City Council member Ralph Remington said there's interest from several suburbs as well.

Remington and other council members deserve praise for raising awareness of trans fat risks; their targeting of chains is good, too, to make sure small businesses wouldn't suffer from a ban's regulatory costs in this difficult economy. But whether a local ban would significantly improve public health is debatable. While Willett and the so-called "food police" group Center for Science in the Public Interest support local action, other experts including some in Minnesota are more skeptical. It's likely a trans fat ban here would lead to restaurants simply switching back to older saturated fats at this point. These still have heart risks and are still laden with calories. Consumers might mistakenly assume they're making a healthy choice because food doesn't contain trans fat when, in reality, they'd still be choosing foods that increase the risk of heart disease and obesity. A ban is a dramatic step, one best left to experts. Instead of making food choices for consumers, Twin Cities politicians should focus on helping diners get the information they need to pick out healthy entrees.

That's where another measure under consideration by the city councils comes in. Both are considering ordinances that would require big-chain restaurants to post nutritional info on menus; there's interest at the state level as well. This is good public policy that should be emulated at the federal level. The menu labeling should include trans fat information as well as calorie counts -- critical information in the fight against obesity. Unfortunately, diners often don't have easy access to this information and don't realize that the supersized portions set before them may contain more than a day's worth of calories.

Leadership is needed from a newly beefed-up FDA on federal trans fat restrictions and on restaurant food labeling. Ideally, there would be a national policy standardizing how restaurants provide this information instead of patchwork regulation. But until there is, action that better arms consumers to make smarter food choices when dining out is welcome and needed.