People have to lose weight to stay healthy. Actors have to lose weight to fit into a role required. They may be already overweight, but they may not be thin enough to fit a character. Actors take the tough road sometimes to get to the weight naturally needed because it is more real than using a belly sucking vest or CGI. This is how they lose weight quickly.
The simplest way is to burn calories and stay in shape by going to the gym or walking around the block for a period of time. Go almost every day for at least an hour, as recommended by doctors, to feel good and sweat a bit. A lot of training to lose with weight is done like the elliptical, bike, and treadmill. Others like to play sports and it is a fun way to enjoy themselves while sweating. Working with a personal trainer keeps them in line and it makes them work even harder because one hour is just not enough.
A Heavy Diet
In other words, no carbs, more protein, and a healthy appetite to follow. Some will follow a vegan diet to shred the fat and shock the body to start with, while others will snack of nuts, veggies, and fruit to keep up the pace. No alcohol, just water is consumed. They will count calories and keeping it under 2,000 is the magic number.
Gwyneth Paltrow has always followed a diet of kale smoothies, which has plenty of iron, zinc, and calcium. When preparing for a film, she wants to look her best, so she is at her most strict. They are also aware of not following a fad diet or anything not legit.
Then, there are the heavy diets, the ones that are quite torturous, but if the role requires to be very skinny, some actors are okay going the hard route. Anne Hathaway ate two squares of dried oatmeal paste when she was prepping as the homeless factory worker of Fantine in Les Misérables.
Michael Fassbinder ate less than 900 calories a day over a three-month span to get into the state of body as Bobby Burns in the aptly named Hunger and, maybe as notorious, he bulked up as Batman for the trilogy, but Christian Bale lost 62 pounds by consuming no more than 300 calories a day to play a malnourished worker in The Machinist. Note: it is highly unrecommended to not go this route.
Losing It Like An Actor
These simple ways allow rapid weight lost, but at a healthy rate rather than a radical rate that some actors go to (also look at Jared Leto in Dallas Buyers Club) to get into character.
It can’t be done two weeks, but within a quick two months in physical preparation of the role. Actors will go to great lengths to fit in it for realism; they rely on the basics of weight loss to succeed.