A few months ago, I read Gary Taubes's Why We Get Fat: And What to Do About It. I've been wanting to comment about it ever since. I found parts of the book very convincing and others less so.
Taubes is a low-carb (practically no-carb) advocate, which is always suspect. The book presents a pretty strong argument against the view that people are getting fat because they eat too much and exercise too little.
I was amazed and convinced by the way that Taubes argues agains the "calories in, calories out" way of thinking about weight change. It's not that he disagrees that you gain weight by taking in more calories than you expend; it's just not a useful way of looking at it, because it doesn't answer the question of why that is happening.
By way of analogy, if you were in some particular room in a museum and after a while you noticed that the room was becoming very crowded, you might ask your companion, "Why is this room getting so crowded all of a sudden?" It would be true but not at all helpful for your companion to answer, "More people are coming in than are leaving." That's how Taubes views the calorie situation.
He points out that, for instance, children gain quite a bit of weight as they mature, yet this is not because they take in more calories than they expend. Obviously they do, but the causality goes the other way - they take in more calories than they expend because they are driven to grow. Similarly, adolescent girls develop fat deposits on their chests and hips, and this is not because they are eating more than they need; they eat more because biology pushes them to in order for them to develop secondary sexual characteristics.
He also points out that something like a 35-calorie-a-day difference (a bite of a brownie, basically) adds up over a 30-lb weight gain (or loss) in 10 years. Given that math, how is it possible that so many people do maintain a consistent weight?
Obviously there are processes in our bodies that balance our food intake and energy expenditure. Experiments with rats show that at least some types of rats can stay fat or thin (according to genetic predispositions) on various amounts of food by modulating their energy expenditures. This is presumably not because the skinny rats read Vogue and the fat rats watch too much television.
Taubes then presents his case that the reason people are getting so fat now is that we're eating so many carbs. His line of reasoning involves insulin regulation. If I remember correctly (which I may not), the basic idea is that eating more carbs causes our bodies to produce more insulin, and insulin promotes fat storage, which is to say it causes (basically) our fat cells to become hungry and thus prompt us to eat more so that they can grow.
I find that argument reasonably convincing. What I found less convincing is Taubes's line of reasoning that goes something like, "Everyone in the past knew that you lose weight by cutting down on starches, before all this low-fat bullshit came along." I agree that the low-fat craze of the 80's/90's was mostly b.s., but I don't find it that meaningful that people have historically known to cut back on starches. It's pretty obvious if you consider what people usually eat (even in the past) that we're much more likely to overeat bread, rice, potatoes, pasta, desserts, etc., than we are to gorge on meats. And of course it's almost impossible to overindulge in veggies. (Most people historically probably couldn't even afford to overeat meat. Also, it's much more fun to overeat starches, IMO.) Of course, that's on top of the general thing that citing the wisdom of the past is always selective.
Taubes's ultimate recommendation is the standard Atkins type of diet, with extremely restricted carb intake. He justifies this partly in the common paleo way - apparently our caveman ancestors mostly ate corn-fed beef from the Safeway, and we should too.
I find the general recommendation to cut back on starches pretty convincing, but I don't find that cutting all of them from my diet is any easier or more possible than keeping myself on a general starvation regimen that makes it impossible to gain weight anyway (even as one of the fat rats). A mostly-meat diet is expensive and, after a while, sort of disgusting, and it's obviously not at all environmentally sustainable.
I also, of course, know plenty of skinny vegetarians and vegans, who are clearly eating very high carb diets, suggesting that there are various types of diets on which one can maintain a healthy weight (even effortlessly, if you're lucky in that way). So...yeah.
But the book is probably worth reading if you're into this type of stuff.