Well, I'm not an expert on the biochemical properties of our food, but here's what I've pieced together.
In terms of weight loss only, all calories may well be equal. That is, 1500 calories of Ben and Jerry's ice cream, if it's all you eat, may help you lose weight.
The problem with some foods, however, is first, they don't "stick" with you. Could you eat 1500 calories of B&
Js (which may be a little more than a pint, depending on flavor) and be
satisfied all day?? Or would you struggle with wanting to eat more? It's a real struggle to stick to the diet if it isn't keeping you satisfied. I think when people have diets full of dense calories like this that they are quicker to fall off plan, announce "diets don't work for me" and quit. When really it's not about the diets or the calories but the choices made.
Second, and this is a related point, some calories provide a lot more nutrition than others and are therefore helpful to our bodies health! So, if you replace 1500 calories of B&
Js with 1500 calories of a combination of lean proteins, fruits and veggies, some dairy for calcium, and whole grains not only will you feel
much more satisfied throughout the day (and more likely to stay on plan) but you are giving your body all kinds of nutrients and phytonutrients. Your cells may repairs themselves, your arteries may start to clean themselves out, your body may just function better top to bottom!! Plus, you may be surprised to find that if you limit those foods like B&
Js to more rare occasion, you will LIKE the other foods more and more and crave the B&
Js less and less. In other words, no one's saying you have to banish those lower nutrition foods altogether.
So that my longish answer for why all calories are not equal.