I’m not a scientist of any kind (although I did kick ass in my high school and college science courses, because I love the topic), but I suspect the reason we’re collectively having difficulty with weight is because of one taste in particular: sweet. I don’t pretend to know the full biochemical mechanism behind it, but I think foods/drinks with a sweet taste impel us to eat more than any other taste, and, because of that, should probably be avoided by people trying to lose weight. Here’s a bulleted list of my observations that point to this.

• Everyone I know that is overweight has a sweet tooth. Friends I know who don’t have a sweet tooth are thinner.
• Sweet-tooth people I know (myself included) are much more likely to binge than people who don’t have a sweet tooth.
• Cultures (like Japanese and Chinese) that don’t eat a lot of sweet foods tend to be thinner than those that do (like tropical islands, Mexico, the United States).
• Pretty much the only dietary change in the American diet that has been consistent in the last half-century is the explosion of sweet foods, sweet drinks (even diet ones), chewing gum, etc. The percentage of fat in our diet, for example, has actually gone down, but sugar has lost its status as a dietary danger because it’s fat-free.
• It would seem that the only source of sweet food until very recently was fruit, which typically has a very discrete harvest period in the wild. So it would make sense to engorge on fruit and even fatten up a bit when it was available, because its availability came in spurts and, unlike grain, was almost impossible to store until refrigeration.
• Fructose, unlike starch’s sugar components (glucose), does not trigger a satiety signal. I think this very much evolutionarily related to my previous point; when mankind has traditionally consumed fructose, it’s been in the form of fruit, and it might not be around for much longer, so chow down!
• NOTHING makes me want to continue eating more than eating something sweet. I read recently in RuPaul’s autobiography that he avoids sweet food for the exact same reason, and RuPaul is thin.
• People who drink lots of diet sodas are actually heavier than those who don’t, even though sodas don’t have any calories.

I know, I know, I know there are lots of people who eat sugar all day long and they never gain weight. There’s an exception to every rule, so I’m focusing on generalizations based on my own personal experience and what I see at societies at large.