I hereby suggest Occam's diet: avoid things that taste like protein but aren't.
So now my theory is that lower Japanese obesity is more a result of a strong sense of cultural conformity rather than something inherently healthy about the diet.
Even their ice creams don't contain much protein. A large McFlurry with Oreo's is 381g but has only 15g of protein (and 85g of sugar).
source: http://nutrition.mcdonalds.com/getnutrition/nutritionfacts.p...
In a practical sense, the question doesn't matter at all to people trying to live healthier lives.
The reason we have fatter people is we have more calorically dense foods readily available (meaning greater calories in) while people live more sedentary lifestyles (means less calories out).
This function to lose weight is so incredibly simple (paging jacques chester and his steam machine blog post).
Why are people running surpluses?
Food is much more readily available and convenient. Look at all the food you can buy. Then look at how much of it can be stored at room temperature, needs no preparation, and has a long shelf time. Then add in all that you can buy that stores in your refrigerator, does not need to be prepared, and has a long shelf life. Lets take it further, look at all the food you can buy, that you store in your freezer, that you prepare by sticking it in a microwave for five minutes.
The abundance of food combined with an excess in idle time, namely the result of a forty hour work week or no work week, leads to over consumption. I always love the farm comparison. Growing up it was eat before light, a big lunch, whatever you grabbed off the tree or stole from the garden, and a big dinner. As a kid if we weren't doing chores we were running off with friends to a game, fishing, or forever building that fort. These days its inside till mom/dad gets home, food everywhere, and an XBOX/PS4/Etc.
Then go look at the people you work with. Its pretty easy to tell why some are overweight. Lunch out every day at the fat festival around the corner, that place that serves 1200 calorie or more lunches for seven bucks. Usually a good chaser for that double donut and coffee with cream breakfast (or bagel with cream cheese). Then those little snacks in the desk.
Its simply calorie overload with nothing but idle time. Hell these same people will make fun of the fitness/diet "freaks".
TL;DR
Idle Time, Endless ready food, results in calorie overload
Caloric surplus equals kilocalories in minus kilocalories out.
But kilocalories in is a function of what you eat, and of appetite, which is itself a function of metabolic processes, which are functions of a lot of variables we don't fully understand, just one of which is what you already ate. And kilocalories out is a function of your voluntary physical activity and your automatic metabolic processes, again based on variables we don't yet fully understand.
So "energy in - energy out" is a gross oversimplification. The implication there is that you can eat less and exercise more to lose weight from stored body fat. And that usually works for most people, but not necessarily for the obvious reasons. But you also have to explain all the counterexamples.
And for that, you have to figure out how the human body responds to specific food chemicals. One food with caloric value might cause the eater to lose weight because it is used for its chemical value (such as for methylation) instead. The same food might cause weight gain later, because the body no longer needs that chemical as much.
Ignoring your ignorance does not make you smarter.
Edit: here's a non-gov funded study, so could be orange, soda or other bias https://www.ncbi.nlm.nih.gov/pubmed/2049981