Story highlights Drivers Mark Webber and Jenson Button have spoken about the difficulty of keeping their weight low

Lighter drivers make it easier for teams to adjust car balance and stay close to the minimum weight

Teams monitor driver weight and can ask them to lose pounds throughout the season

How would you feel if your boss asked you to lose weight so you could carry on doing your job?

That is the reality facing Formula One drivers whose body mass is constantly checked by their employers, the teams.

Leading drivers, including 2009 world champion Jenson Button and Red Bull racer Mark Webber, spoke openly about the problem.

Earlier this month Webber commented on this Twitter page: "Haven't eaten for last 5 years!" He later removed the tweet.

"I love fitness training but there are things I can't do because I have to be a set weight -- not eat carbohydrates, not build muscle," Button told reporters at the Korean Grand Prix , in the city of Mokpo, South Korea.

"I struggle to meet the weight limit. I have done for three years."

Driver weight is a hot topic because next season's redesigned car are heavier.

That means lighter drivers -- such as Felipe Massa, who weighs 59 kilos, will have an advantage over taller drivers like Nico Hulkenberg, who weighs in at 74 kilos.

Just like horse racing and boxing, motor racing has scales to balance.

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The car must meet a minimum weight of 642 kilos -- the weight of the car and driver combined without fuel -- to help level the competition but the further the car tips over this ideal weight, the slower it becomes.

Teams also like to have the leeway to add ballast to adjust the balance and handling of the car for each circuit.

The preference is for the car and driver to weigh in below the minimum weight and for ballast to make up the difference. The heavier a driver is the less ballast the teams have to play with.

Weight problem

One way to lose weight is to ask the driver to get skinny -- and this can go on all season long.

"This year we had a problem with weight," Carlos Corell, who manages Caterham ( a team sponsored by CNN) driver Giedo Van Der Garde's fitness regime and diet, explained to CNN.

"We try to develop the car but sometimes that means the car is going to be heavier, so when the car is heavier the only way to lose weight is the driver.

"Giedo is one of the tallest drivers on the grid. He is 1.83m. He is around 73.5 kilos with his helmet and overalls on. It's really light.

"We had to lose one and a half kilos -- and that's what we did."

Highly rated Sauber driver Hulkenberg is, like Webber, Button and Van Der Garde, one of the taller drivers on the F1 grid. The German measures 1.84m.

His former manager Timo Gans told CNN that, just like Van Der Garde, Hulkenberg had also been asked by a team to lose weight during the season.

"In 2011, when Nico was third driver for Force India, I spoke to [someone] in a leading position at Force India," Gans explained.

"He told me that they had noticed that Nico's weight had changed a little bit.

"He had gained one and something kilos in two or three months. I was advised to make sure that Nico get his weight back in the limits."

A Force India spokesman told CNN: "Drivers are encouraged to be as fit as possible without sacrificing strength or endurance."

While it is not known exactly how many drivers have been asked to lose weight, Gans explained that teams regularly check a driver's weight.

During the televised races, drivers are shown standing on the scales to be weighed by the sport's governing body, the FIA, when they get out of the car.

"During the race weekend we check it [the driver's weight] one, two, three, four, five, six, seven times," counted out Corell. "It's because the team needs to know the weight of the car and the driver."

When asked how often he would check Van Der Garde's weight away from the race weekend, he said: "No more than twice a week."

F1 fitness plan

Weight is just one of the reasons why modern F1 drivers dispel the myth that is the car doing all the hard work.

Today's drivers are toned athletes who train to achieve a carefully balanced lean body built for both stamina and strength.

"The training we do is not to increase the muscle but to keep the strength and it helps to lose the fat," explained Van Der Garde's trainer Corell.

"We do cardiovascular training -- cycling, running, swimming and rowing -- and do weight in the gym to increase strength.

"During the season, his training program will be around four days a week cardiovascular, one or two days of strength training and one day in the simulator.

"We keep the weight overall with the diet. We follow quite a hard, strict diet."

Shattering another popular myth surrounding a racer's champagne lifestyle, guzzling fizz is generally reserved to the podium's post-race celebrations.

"If we had a really, really good weekend we could go for a beer but it's not recommended," said Corell.

"The diet is a mix of carbohydrates, proteins and fats, good fats like olive oil and avocado.

"We try not to eat pasta, white rice or potatoes. We use vegetables, brown rice or quinoa. We use fish and chicken and twice a week he can take red meat.

"We work hard to keep the weight. If you want to be in Formula 1 you have to push, you have to train harder than the rest, you have to take care of the diet more than the rest -- you have to do it."

Teenage traumas

With all this focus on weight, it would be no surprise if the physical battles caused mental pressures too.

Former McLaren and Red Bull racer David Coulthard revealed in his autobiography "It Is What It Is" that as a teenager he put himself through a severe weight strategy that he likened to the eating disorder bulimia.

"It was an essential part of being an oversized teenager in karting making weight," Coulthard, now an analyst for the BBC, told CNN.

"I would have my dinner, weigh myself and if I was too heavy I'd go swimming and exercise and try and control my weight by being sick.

"When I didn't have to do it anymore I didn't do -- why the hell would you do it when you didn't have to?"

Coulthard's experience may be on the extreme end of the scale. He is the only driver to speak openly about his very serious issues with weight.

"There is of course a little bit of stress," added driver manager Gans, who also works with up and coming racers.

"The drivers have to look after their weight even when there's no race, during the summer and winter breaks.

"They cannot just gain two or three kilos -- that is just impossible. But they are able to handle it; they're professional athletes, so it's normal."

But there are already anxieties among the driver community that weight could become a bigger issue in 2014.

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Next season's switch to a turbo engine and a more powerful kinetic energy recovery system [KERS] has already seen the FIA increase the minimum weight of the car to 690 kilos, without fuel on board.

The battery powered KERS system, which gives the cars an extra boost of power, was first introduced in F1 in 2009, adding an extra 35 kilos in weight to the car.

Ahead of the 2009 season drivers including Fernando Alonso, Rubens Barrichello and Robert Kubica all spoke about shedding pounds to compensate for the car's weight gain.

The increased hybrid technology and turbo engines on the horizon in 2014 are again fattening up the cars.

However, it has emerged that some teams are already struggling to meet the new minimum weight for the car -- not the news F1's taller and heavier drivers wanted to hear.

"It is a concern for a driver like me," Force India's Paul Di Resta, who is 1.85m, told reporters in Korea.

"I am three or four kilos under what I would like to be to be healthy.

"It's a little bit of an unfair advantage to be a smaller guy. I'd like to see the weight limit raised."

Coulthard agreed the sport's technological evolution does not come without a cost.

"The weight of the packaging, the KERS, the battery, you carry more stuff," he added: "You don't get anything for nothing.

"I know Mark Webber has struggled to get more of a weight distribution than Sebastian [Vettel] had a couple of seasons ago because of the design of that car."

Neither Hulkenberg nor Di Resta have been confirmed as drivers for 2014.

The pair are fighting for seats with smaller drivers such as Felipe Massa -- could being taller and heavier impact on their ability to keep their place on Formula 1's fickle grid?

"We're more interested in the talent and potential of a driver rather than the difference of a few kilos," said Lotus team principal Eric Boullier.

"It's way too early to say that anyone is not in F1 because of their size," agreed Coulthard.

"There is no substitute for speed but if you've got two guys who you believe to be the same speed but one is smaller and 10 kilos lighter then why would you not take that person?

"If someone is taller and faster then, of course, [the team] are going to take that guy and work their engineers harder to try and come up with weight saving solutions."

Driver manager Gans, however, warns the next generation of young talent must measure up if they are to even get a sniff at being a professional racer.

"If you notice [a driver] is very tall then you get suspicious at once," Gans explained.

"A driver that is 1.90m or taller probably wouldn't even come this far to have a manager. He wouldn't even win races."

Asked if extreme dieting or disorders were widespread in motorsport, Coulthard summed up: "I suspect more and more young racers are doing it than in the higher formulas, where you do need to have the strength."

In the highly competitive precision world of F1, the driver is in danger of becoming another component that must be the perfect fit.

"It's topical not because it's tough on tall drivers or heavy drivers this year, but because it's become more and more of an issue," warned Coulthard.