Dan Charles

Many big food companies are caught in a dilemma these days. They want to rebrand themselves as merchants of health — Coca-Cola's new anti-obesity ads are just the latest example — but many of their profits still come from products that make nutritionists scowl.

If there's one person who symbolizes this tension, it's Derek Yach.

It's amazing how many different kinds of people have been trying to abolish or at least change the government's payments to farmers. They include economists, environmentalists, taxpayer advocates, global anti-hunger advocates and even a lot of farmers. Some have been fighting farm subsidies for the past 20 years.

This past year, those critics laid siege to offices on Capitol Hill because the law that authorizes these programs — the farm bill — was about to expire. (It has to be renewed every five years.)

Now that the Christmas feast is over, you may be looking at all the extra food you made, or the food that you brought home from the store that never even got opened.

And you may be wondering: How long can I keep this? What if it's past its expiration date? Who even comes up with those dates on food, anyway, and what do they mean?

Here's the short answer: Those "sell by" dates are there to protect the reputation of the food. They have very little to do with food safety. If you're worried whether food is still OK to eat, just smell it.

Have you noticed, perhaps, that some of your store-bought salad dressings or spaghetti sauces taste a little less salty lately?

Probably not. The companies that make those products are doing their best to keep you from noticing. Yet many of them are, in fact, carrying out a giant salt-reduction experiment, either because they want to improve their customers' health or because they're worried that if they don't, the government might impose regulations that would compel more onerous salt reductions.