 The vast majority of studies on daily nut consumption and weight have shown no significant weight gain in the short or long term. But doesn't that violate some pesky law of the physical universe? Conservation of energy isn't just a good idea, it's the law. The first law of thermodynamics. Energy can neither be created nor destroyed. It is a law that cannot be broken even by the most hardened nut cases. Calories can't just disappear. One solution offered to the mystery of the missing calories has been dubbed the pistachio principle. Maybe nuts are just such a pain to eat. For example, in-shell pistachio slow the rate of consumption because of increased preparation time and this may permit greater metabolic feedback during the ingestive event that augments the tidy with the potential to reduce the energy content of the eating event. Meaning, in-shell nuts slow you down so much that it's time to think, hey, I'm eating, but not eat too much. Yeah, but what about shelled nuts? Well, you still gotta chew them. A study out of Japan suggested that increasing dietary hardness, meaning difficulty of chewing, was associated with lower waste circumference. Now your jaws do burn some calories, but it's not much exercise. I mean, I guess if all you ate was raw cabbage all day, you'd lose some weight, but there ain't many calories to begin with. So it may just be the tedium of chewing that leads one to eat less. Then there's the fecal excretion theory. Many of the cell walls of chewed almonds, for example, remain intact in the digestive tract. So even though a nut may technically have a certain number of calories in it, maybe they just go out the other end and you don't absorb many of them. To test both these theories, all scientists would have to do is compare weight gain from nuts to weight gain from nut butters. Stay tuned.