as a young man like in streetcar he almost looked like a bodybuilder. In the 60's he had a very slight weight problem that was not more then up and down 25 pounds.
In 1972 he did Last Tango at age 48. He did several near nude scenes and looked good and was even athletic.
Then 4 years later he showed up for Missouri Breaks and looked like he gained 100 pounds, then as years went by he just got bigger.
What happen to him between 1972-1976?
I just read about his eating habits and it's no wonder he put on so much weight. During the filming of One Eyed Jacks he ate two steaks, potatoes, two apple pies and a quart of milk for dinner every night. He also loved ice cream and could eat a shitload of it in one sitting.
Even if he ate a lot in the 60's, youth, metabolism and possibly genes kept him fit. He gained some weight over the 1960s but stunned everybody by appearing quite thin in a bad movie called "Night of the Following Day." Then, as noted above, he "held down" his weight for The Godfather and Last Tango...4 years later, the weight arrived.
The thing to remember here is that movie stars -- and let's say male movie stars for the sake of argument -- were held by the studios to health regimens that REQUIRED them to eat right, exercise, and even take pills to reduce water in the body, or other diet pills.
As movie stars became more independent in the 50's and 60's, studio control over their health regimens started to wane.
Most stars took care of themselves and ate right and exercises of their own volition.
But a few "let it go." It is a testament to how fit most movie stars are that only a few gained noticeable weight: Brando(in the lead), Nicholson, Travolta and, recently, Russell Crowe.
The rest are either thin to begin with, or very health conscious. Clint Eastwood has made it to 91 as a leading man(Cry Macho) after a life of diet, weights...and vitamins.
It seems clear that Brando just reached a point where he didn't care about his weight anymore. He kept a handsome face for the rest of his life and was filmed a lot in close-ups and shadows. He kept that great voice. And producers kept hiring him because he was a "living legend."
Side-bar: in the 70's when he was "retired" for a few years and not required to be on screen, Steve McQueen gained some weight(you could see it in photos.) He said "fat means I'm rich and can do whatever I want." He lost the weight for his return to movies with Tom Horn and The Hunter. And soon died young at 50 of cancer.
Side-bar: During some luncheon interview, Warren Beatty ordered very little to eat, and told the reporter: "I have to stay thin. I can't get away with weight gain like Nicholson can." Its tough being a matinee idol!
Side-bar: in one of his autobios, Tony Curtis said it was much harder to be a film actor than to be a film director..."because an actor has to stay fit and thin to appear on the screen for as many years as possible. That's hard work."