Great observation in this article:
“In a perfect world it makes perfect sense. If you consume more energy than your body needs, then according to the central tenet of Einstein’s most famous equation it’ll be turned into mass – a wibbly-wobbly type of mass around your belly and thighs.
The problem is that our bodies don’t burn energy with the consistency of a Bunsen burner. “We do not absorb all the nutrients from some foods,” says Pete Wilde, a professor at the Institute of Food Research in Norwich. “By chewing and eating whole almonds, for instance, we absorb only around two-thirds of the energy listed on the label. The calcium in milk and dairy products reacts with fatty acids and again reduces the energy absorbed.”