Now I have to say I think the BBC "People men made us thin" series has been great, and in many ways music to my ears.
The dogma are:
(1) Eating too much makes you fat.
(2) Exercise makes you thin.
Do diets make you thin?
(1) They have gone some way to debunk this in the program. Of course they have taken an extreme attitude. If you don't eat, you will loose weight, but the psychology of dieting is more complex. The study designs are difficult too. So they studies showing diets don't work will usually say "here's a dieter 2 years later and they have put on 10lbs/5Kg, but here is a non-dieter and this person put on zero weight: ergo, dieting doesn't work".
There is a fundamental flaw in this argument though. The people who diet typically have weight control issues and were always going to put on more weight than people who have never had a problem and never diet!!
So my bottom line would be that dieting is in no way all that it is cracked up to be, but if you are over-weight it is better to try and reduce your calorie intake than to just give up!!
(2) Does exercise make you thin
Again the program takes an extremist view of this issue. I it is true that exercise is a really slow and relatively ineffective way of loosing weight ...but it depends on the exercise, and whether it was the only lifestyle change you made. Really this is a life-style thing. To simply drive to the gym 3 times a week and burn off a few hundred calories is not going to make a significant contribution to a serious weight problem. Those few hundred calories could easily be swallowed up just by one post exercise trip to Starbucks. If you control calories and do more exercise, the exercise will prolong your life and keep you healthier, but really its the calorie-control bit that will knock off the pounds. Turn down that free chocolate bar at the checkout and you have just saved the equivalent of about a two mile run!
Your genes profoundly affect your weight. This is mostly by changing the appetite control systems in your body. Potentially there are many drugs which could change this, but it's not a great idea just yet, because these drugs tend to do too much other stuff. ..i.e., "side effects".
All this lot is just the same for your pets too. It's really important to give a dog a great walk or two every day... but weighing their dinners are the secret of weight control!!