Daniel 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.

For years, the biotech giant Monsanto has provoked outrage among its critics for suing farmers who save and replant seeds, such as soybeans and canola, from the company's patented Roundup Ready crops.

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.

Nobody really wants to think about economics, the famously dismal science, while sitting down at a table loaded with love and calories. Like it or not, though, supply and demand drive food production and set the price of dinner.

So, in a season of feasts, what are the business stories on your holiday menu?

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.

Salt is one of those dangerously tasty substances. We add the magical crystals of sodium chloride to almost everything that we cook or bake, and according to many public health experts, we add too much.

They want us to cut back, to lower our risk of heart attacks or strokes.

Yet when you really start looking for ways to do this, you run into a paradox and a scientific puzzle.

First, the paradox. Too much salt may kill us, but our bodies need some of it to survive.

If you're looking for a dash of optimism about the future — and who isn't, these days? — you can find it in a rosy new prediction about the planet's ability to produce food for the next half-century.

A few days ago, two big names in food policy squared off for a formal debate on the following proposition: There is a fundamental and irreconcilable conflict between the food and beverage industry's interests and public health policy interests on obesity.

A few months ago, I let you in on a little secret about Greek yogurt. Not all of this extra-thick, protein-rich yogurt is made the old-style way, by straining liquid out of it it. Some companies are creating that rich taste by adding thickeners, such as powdered protein and starch.

French adventurer-scientist Roland Bourdeix has a grand, almost surreal, vision for how to preserve a thousand or more genetic varieties of coconut trees. Imagine, as he does, turning dozens or hundreds of remote Pacific islands into coconut sanctuaries. Each island would contain just a few varieties of these trees. No others would be allowed, because the whole point of this exercise is to prevent uncontrolled mixing of genes from different varieties.