The Tamil film I hit the headlines for a host of reasons last month. One, of course, was the fact that it had garnered Rs 55.6 crore within the first three days of its release. But another reason was its hero - Vikram. The immensely popular star was in the news for shedding 26 kilos and then regaining 30 for the film.

Director Shankar's film tells the story of a bodybuilder, played by the southern superstar, whose character weighs 110kg in the film, and then becomes half his size.

Vikram told the media that for this role he had adopted a "starvation diet", drinking mostly juices. He went down from his usual of 82kg to 56kg and then went up to 86kg within a span of two years. For a song, he weighed 110kg (which was done with prosthetic make-up). "When I am playing a particular role, I like to look like the character rather than like myself," Vikram, 48, said.

In the world of cinema - Bollywood and its regional cousins - actors go off food to quickly lose weight. It is the film world's worst -kept and best-kept secret - everybody talks about it, but few are ready to go public on this. The Telegraph tried to get the reactions of many stars who have shed kilos by literally starving themselves. Nobody replied.

But talk to anybody in the Hindi film industry and they'll whisper about these diets followed by some top stars.

"I can say that at least 90 per cent of Bollywood stars would have had adopted such diets at one point or another," Mumbai-based fitness expert Deanne Pandey says.

A top actor is known to go off salt completely before a shoot. This, he believes, gives the lean look that he needs to show on the screen. Another beefy and muscular actor known for his physique starves before a shoot. "He tells us: I have no energy even to talk," a friend says. "Sometimes he says that he just goes through the motions of acting."

Many don't eat a normal meal any more. Some eat only egg whites, whey protein, tiny portions of vegetables and the rare piece of chicken or fish. They take in loads of vitamin supplements to make up for the nutrients they are not eating.

"Often starvation diets are the only way to lose a lot of weight in a short time frame," says Abhishek Sharma, a personal trainer who has worked with Bollywood stars such as Ranbir Kapoor and Deepika Padukone.

Health experts point out that the amazing muscles you see on your favourite actor's body - bulging biceps and sculpted abs - are often the result of a mix of steroids and a very austere diet.

But the problem is that these muscles have not been built over time, as they are meant to. "It takes years to build six-pack abs," Pandey says.

The male body - with a naked torso - has been ably showcased in recent years by the three top Khans of Bollywood - Salman, Aamir and Shah Rukh. Salman's shirtless acts started the trend - and Shah Rukh Khan followed by displaying his six packs in the 2007 film Om Shanti Om. Aamir Khan took it a step further by showing an eight-pack-frame in Ghajini (2008).

Shah Rukh, whose rippling muscles in the 2014 film Happy New Year ( HNY) were the topic of much discussion, is believed to have eaten sparingly and exercised "like a maniac" before the film. The result was a body that even a Mr Universe would covet.

"In the past female bodies were mostly on show. But now heroes too are going bare. Think of the number of times SRK goes shirtless in HNY," points out Rajinder Dudrah, a senior lecturer in screen studies at the University of Manchester.

Actor Sonu Sood, who has been exercising for more than 20 years, since he was in college, believes in eating balanced meals and exercising for a fit body. But for a full year he survived on salads to achieve his ribbed eight-pack abs in HNY.

"It is very important to eat less and right for a lean look. The diet has to be very strict. No carbs, live on salads and do lots of cardio exercises," he says. "Since the actor's body has to look sharp, he also has to cut out water and salt from the system for the shoot for a ribbed look."

Many follow this regimen. A director recalls how surprised he was when he was invited to a meal by an actor who has made a comeback in recent years. The 50-something actor was known in the industry as someone who seldom ate. But when the director entered the actor's vanity van, he found that placed in front of him was an array of dishes - like a veritable feast. "I am breaking my fast after God knows how many days," the actor explained. "Today I am going to binge."

Pooja Makhija, a popular Mumbai-based nutritionist who advises Bollywood stars, doesn't take names, but recounts that she lost stars as clients because she refused to give into their demands of what is known as yo-yo dieting. "They are scared when I tell them that they have to eat at least six meals a day and that carbohydrates should be an integral part of at least three meals," Makhija says.

The industry wallahs stress that actors don't always choose to go on such austere diets, but are forced to do so. Peer pressure, strict deadlines and the huge amount of money riding on a film often make stars get into such acts. Shankar's I is the costliest ever Tamil movie made at Rs 220 crore and was released in 10,000 screens. "The stakes are high and so one can't totally blame the actor," Sharma says.

Very often, it's a role that pushes an actor to drastically lose weight. Reports said that Amitabh Bachchan, a proponent of method acting, lost weight for the role of an anti-corruption crusader in Satyagraha. The character he played in Prakash Jha's film was that of a man on an indefinite hunger strike.

Ajay Devgn in Action Jackson had to lose 17kg so that he could go shirtless. The director of the 2014 film, Prabhudheva, had once remarked that Devgn did not seem interested in food. The actor had shot back: "How can I when he wants me to lose 17 kilos for bare body shots?"

The problem with such diets is the grave impact they have on one's health. "Losing a lot of weight leads to mood swings. Your muscles become weak and your kidneys and other vital organs are affected," Makhija says.

A sudden loss of health can lead to back injuries and bone problems. "Many superstars have suffered because of unhealthy dieting and extreme workout," says Pandey, who has worked with stars such as Bipasha Basu, Abhay Deol and Lara Dutta. Basu had told reporters earlier that she had gone on a crash diet to lose weight - but ended up damaging her knees.

Rahul Bhatt, who coined the term "body confidante" for himself, believes that starvation diets and size zero bodies are the ugly realities of Bollywood. "These are occupational hazards. The pressure from the public and the media is too much and the actors get into this without realising the long-term harm the starvation diets are going to do to their bodies."

Director Mahesh Bhatt's son was himself an obese teenager but walked off his excess weight before switching to the gym. "It is not merely the A-listers who take performance-enhancing drugs like anabolic steroids for instant body transformations but also Bollywood wannabes who are trying to fit in," he says.

There is growing concern about these diets also because the actors are not just harming their own health but endangering that of their fans who look up to them.

"A host of people develop serious body image problems as a result of the examples set by film stars. Girls as young as eight or nine have been brought in by parents because they are scared that they will put on weight if they eat and then friends will laugh at them," Delhi-based psychiatrist Sanjay Chugh says.

For many girls, size zero is the benchmark, rues Jagmeet Madan, principal, department of food and nutrition, SVT College of Home Science, SNDT Women's University, Mumbai. A 2010 study by the college revealed that most girl students in private schools were obsessed with the size zero figure then flaunted by actress Kareena Kapoor. "We were aghast to learn that the obsession starts from Class IV or Class V. Image is uppermost in their mind. And they are adopting all kinds of unhealthy means for this," Madan says.

Youngsters should perhaps look up to someone like Akshay Kumar, who makes no bones about his distrust of starvation diets and bulging muscles. At 47, he lives a disciplined life - he goes to bed on time and wakes up before dawn for a run on the Juhu beach. "But there are actors I know who are writing their regimen based on how many pills and protein shakes to take," he'd said in an interview.

On the other hand is Vikram, who told the media that his diet left him "angry" and "sleepless". The National Award-winning actor craved food and went to bed before 9pm so as not to think about food. "There were days when I was starved to the point of losing my mind," he said.

DIET THEIR WAY

Katrina Kaif: She sticks to a macrobiotic diet which includes eating grains with vegetables and grilled food. She stays away from refined or processed foods

Bipasha Basu: Has warm water in the morning, followed by tea, and almonds soaked overnight. She has rice only on her birthdays and eats dinner before 7pm

Kareena Kapoor: She eats small portions and has sprouts every two hours to boost her metabolism. She drinks eight litres of water a day

Nargis Fakhri: She did a six-day juice cleansing diet and lost 3kg in a week

Sonam Kapoor: She said in interviews that she had bad eating habits and has almost starved herself, drinking only juices and foregoing carbs to lose weight