In a recent study, Smart Money compared various fast-food items on the basis of how much they cost for each 100 calories. The study found that the cheapest items usually had the fattiest calories, while the most expensive ones were much healthier. In a particularly surprising twist the falling price of lobster has brought it almost within range of fast food.

On the cheapest end of Smart Money's scale, a 32-ounce coke from Subway delivered the most calories for the cheapest price. In fact, at only 38 cents per 100 calories, it was almost 75% cheaper than the top-ranked item. What's more, with zero calories from fat, it was among the healthier choices, although the absolute lack of nutrition and massive amount of empty calories make it far from an ideal dietary choice.

Reading through the calorie/price comparisons, a few things quickly become clear. First, while the price per calorie is an interesting measure, it definitely has to be taken in tandem with the amount of calories that come from fat. Nutritional guidelines suggest that, ideally, 30% of calories should come from fat. The healthiest meal in the study, McDonalds' Premium Southwest Salad with Grilled Chicken, gets only 29% of its calories from fat, but costs far more than other dishes. In fact, at $1.47 per 100 calories, it is the most expensive per-calorie dish on the menu.

By comparison, the cheapest food item, a White Castle Cheeseburger Slyder, costs 41 cents per 100 calories, but derives 47% of its calories from fat. Granted, at 170 calories per sandwich, it has far fewer calories than a 360-calorie Southwest Salad. Then again, who eats only one White Castle Slyder?

In terms of big, bad sandwiches, McDonalds' flagship burger, the Big Mac, came in at 74 cents per 100 calories, 48% of which came from fat. By comparison, Burger King's Double Whopper with Cheese cost only 49 cents per 100 calories, but derived a massive 59% of its calories from fat. It's also worth noting that, at 1,010 calories Burger King's gutbuster was almost twice as heavy as the Big Mac's 540 calories.

Ironically, lobster, which has long been among the most expensive of delicacies, is now almost within range of the Southwest Salad in terms of cost per calories. Because of a combination of factors, lobster currently retails for between $7 and $9 per pound. Given that a pound of lobster meat contains roughly 446 calories, the cost per 100 calories is roughly $1.79. What's more, just under 6% of the calories in lobster come from fat.

At those prices, maybe Long John Silvers should bring back their "Buttered Lobster Bites." This time, they could even afford to use real lobster!