I don't mean to discourage anyone, but 90% of people who lose weight on diets end up gaining it all back, and then some.
The problem is twofold.
1) Whatever you did to lose weight is something you need to do for life. It's not a "diet" that you go on to lose weight, then go back to eating "normal." Whatever you did before the diet is what got you overweight in the first place. Stick with what lost the weight, just add enough more food/calories to maintain your weight.
2) If you lose weight too fast, you kill your metabolism. The biggest losers lost hundred+ pounds during the season and they're all back to their previous weight. When the researchers looked at their metabolisms, they were significantly lower than they would be for a person of their height, age, and weight. By a lot. This is a giant hole you're already in. It doesn't take _that_ much extra food to really put on the pounds after losing weight.
http://www.nytimes.com/2016/05/02/health/biggest-loser-weight-loss.html?_r=0
After ‘The Biggest Loser,’ Their Bodies Fought to Regain Weight
Contestants lost hundreds of pounds during Season 8, but gained them back. A study of their struggles helps explain why so many people fail to keep off the weight they lose.
(the relevant bits follow)
“It is frightening and amazing,” said Dr. Hall, an expert on metabolism at the
National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health. “I am just blown away.”
It has to do with resting metabolism, which determines how many calories a person burns when at rest. When the show began, the contestants, though hugely overweight, had normal metabolisms for their size, meaning they were burning a normal number of calories for people of their weight. When it ended, their metabolisms had slowed radically and their bodies were not burning enough calories to maintain their thinner sizes.
Researchers knew that just about anyone who deliberately loses weight — even if they start at a normal weight or even underweight — will have a slower metabolism when the diet ends. So they were not surprised to see that “The Biggest Loser” contestants had slow metabolisms when the show ended.
What shocked the researchers was what happened next: As the years went by and the numbers on the scale climbed, the contestants’ metabolisms did not recover. They became even slower, and the pounds kept piling on. It was as if their bodies were intensifying their effort to pull the contestants back to their original weight.
Mr. Cahill was one of the worst off. As he regained more than 100 pounds, his metabolism slowed so much that, just to maintain his current weight of 295 pounds, he now has to eat 800 calories a day less than a typical man his size. Anything more turns to fat.