I might very well be wrong, but I think if you eat out most days then it will be very difficult to control weight gain, at least for most people. I think old fashioned home cooked meals are the way to go, but obviously many Farang who live here can't be bothered, and in the case of those who have Thai wives, their wives mostly don't know how to cook Farang style food.
Also, people are quick to blame fast food joints for the world's weight gain problems, but I know countless Thais who have never set foot in a Mc Donalds, a KFC, and etc. and yet they are far overweight. My own MIL never touches fast food, and instead, eats most vegetables, Thai soups and so on, and yet she is well overweight. I personally put it down to eating too much, or at least too often. Unless you are seriously active all day, there is no way your body can burn off 148 meals lol. I also think part of the problem in Thailand is the fact that they are eating a huge amount of rice each day, bearing in mind that rice is loaded with carbs.
I look at some of my Thai neighbors and I see most of their kids are overweight, even though they eat mainly rice and a very small helping of chicken, mince, or etc. My kids, on the other hand, eat a relatively healthy diet, and they are far from being overweight. To be honest, though, I should be getting them to eat more vegetables, but old habits die hard, and I come from a country where virtually the entire population consumes a lot of meat. As a result, meat is probably the dominant food in my home.
And last of all, I think some people just aren't engineered to be overweight, particularly if they don't end up being overweight during early childhood.
By the way, I have two lifelong friends who became seriously overweight, and both of them went on the Atkins diet. I am not saying it is the right thing to do or not, but the amount of weight they lost was incredible, so obviously the diet does work, but once you stop the diet, you gain weight again unless you make the necessary lifestyle changes.
Anyway, good luck with your mission.
PS: Please excuse any spelling or typo errors. It's too damn early for me to be bothered checking and correcting.
Don't try to impress me with your manner of dress cos a monkey himself is a monkey no less - cold fact