The mechanics of weight gain and loss are fascinating. Every time I read an article like this it makes me appreciate the complexity of the human body even more.<p>That said, the issue as a whole is not rocket science, and should not be treated as such. While it is very interesting to examine and discuss how the human body treats various types of calories, at the end of the day the closed system that is the human body is still governed by calories in minus calories out. It is <i>impossible</i> for someone to continue to gain weight if they are eating less calories than they are consuming. Literally. Impossible.<p>The problem is one of human psychology, both at the calorie consumption side and calorie burning side.<p>On the consumption side, there are two main causes. First, for overweight and obese people, the act of putting food in their mouths and drinking high-calorie drinks has become so second nature that their minds simply stop registering it after a while. This is why in scientific studies and surveys that examine the topic, overweight and obese participants massively under-report what they ate throughout the study while those who have trouble putting on weight (the so-called "hardgainers") over-report it. The mind underplays the importance of events and situations it is familiar with (such as eating) and vice versa.<p>The second reason is that even when people do pay attention to how much they are eating and count the calories <i>at that moment</i>, they are terrible at estimating their daily or weekly intake. They try to do "mental accounting," the most common example being "I ate a salad at lunch today, so it's OK for me to order some fries at dinner." For obvious reasons, this approach fails hard.<p>There's also the calorie burning side. Just like most people are terrible at estimating how much they are eating, they are also terrible at estimating how much they are burning. For example, walking counts as exercise for a surprisingly large number of people, yet walking for an hour straight at moderate pace burns only about as many calories as in a slice of bread. And yet the mental accounting comes into play afterward during dinner and they justify their bad habits by telling themselves they exercised that day.<p>There are other issues, such as the way food companies manufacture their products in very specific ways so as to maximize their consumption, or the way they market to children. But in my opinion these are at the periphery. Ultimately the matter is about the individual. It's about how much they individual eats. Not what they <i>say</i> they eat, but what they actually eat.