It's not about calories, it's about blood sugar management
Nutrition is such a central topic of conversation not just for fitness, weight loss, and personal training but also for disease development, healthcare and the well being of our environment. It affects so much, I could write every day for a year and not cover all the important aspects of food.
Let's start with one big idea: food and weight loss.
I recently read Gary Taube's book titled "Why We Get Fat", wherein he explores evolution of nutrition theory, conclusions on how hormones affect cellular metabolism, and what kinds of diets produce what kinds of results. He does an exceptional job describing some complex processes (like fat storage) and the effect insulin has on all kinds of processes.
Do calories matter?
The moral of the story is that calories are less informative to the quality of a person's diet than their meal choices regarding protein, fat, fiber and sugar. Fundamentally, the more concentrated the sugar in your diet (in terms of how much of what you eat is sugar compared to protein, fat and fiber), the greater your insulin response. The more insulin in your system, the more aggressively that you body stores fat. There are some variables that you can control to ensure that you don't become insulin insensitive, namely eating a healthy helping of good meats and fibrous veggies.
Incidentally, insulin also affects the low density lipo-proteins (LDL molecules that carry cholesterol). Elevated insulin levels fill them up and cause them to become heavy, dense, and stick in artery walls (atherosclerosis). When Stanford published its own A to Z diet study, folks on the Atkins diet lost the most weight as well as having a decrease in blood pressure and triglycerides, and a favorable change in HDL/LDL ratios (more good cholesterol than bad).
This bodes well for Paleo eaters and their ilk.
While we know fatty foods don't make you fat, there is some interesting evidence to suggest that more fat from animals, more protein and fiber can bring your body back into balance and out of fat storage mode.
Don't waste time counting calories if you can help it.