I'm confused by all the diet information I've been reading. A lot of people say the only way to lose weight is to cut calories, and yet a lot of the newer books tell me that calories don't count. What's the real deal?

Both points of view have a little bit of truth in them, and both are incomplete. A little bit of history is in order.

The concept of the calorie was first discovered in the 1890s, when food was broken down into its "macronutrient" components (fat, carbohydrate and protein), and the caloric (or "energy") value of each was determined. In the early 1900s, a chemist at Yale University applied the concept to exercise so that there was a way to objectively measure and compare both intake (food) and output (activity). The concept of counting calories was born, and for most of the century, "energy balance" (calories in, calories out) has ruled as the most popular theory of how people gain, lose and maintain weight.

Hundreds of weight-loss diets have come and gone over the years, and most of them have been based on a low-calorie diet. And although some people have always challenged the calorie as the ultimate arbiter of weight loss, it seems that these challenges have gotten bolder, more frequent and more popular in the past decade or so.

And with good reason.

The basic argument against the calorie as the most important factor in weight loss is this: Calories alone don't account for how various foods effect the body. We now know that the food we eat has an impact on mood, ease of digestion, immunity, water retention, energy, blood sugar levels and the all-important hormones glucagon and insulin.

Measuring the value of your food only by how many calories it contains is like measuring the value of your best friend by how much money she makes. It is a one-dimensional way to look at a complex entity.

In their backlash the supremacy of the calorie, researchers and popular writers began claiming that "calories don't count." Instead of saying "calories aren't everything," they said "calories don't matter at all." Fat was the new demon (it has more than twice the calories of protein and carbohydrate), and the popular diet strategy was to keep your intake of fat as low as possible and not worry about the calories.

So what's the "truth"?

If you ask me, designing a weight-loss program solely based on calories is downright silly. On the other hand, it's equally foolish to assume that simply because you're controlling insulin levels and keep a hormonal balance in the body that favors fat loss, you can eat 10,000 calories a day and not get fat.

If you ask me, I would say that the people making the most sense right now are those who are designing food plans that take into account the effect of food on hormones such as insulin and glucagon. That means a plan higher in good-quality fat and lean protein than is "conventionally" recommended, and lower in carbohydrates, particularly "high glycemic" carbohydrates. This means a plan that stresses fiber, fresh vegetables, moderate fruit, plenty of protein, lots of omega-3 fats from fish and flax, and foods such as nuts and seeds, with a fair percentage of raw foods, and an absolute minimum of processed and refined foods, especially baked snacks and other trans-fat-loaded "food products."

Does this mean "calories don't count" at all? No. But it does mean that they no longer belong on center stage.

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