Oil companies including offshore giant Transocean are targeting overweight rig workers after they have had to put on more flights to deal with heavier passengers.
The North Sea helicopter fleet is already under strain because of the grounding of the EC225 Super Puma fleet last year.
The oil firms are working with occupational health company Innovative Health Solutions (IHS) to help employees lose weight.
IHS director Louise Martin said if helicopters had to “ditch” in the sea, passengers with bulging waistlines could cause a disastrous blockage.
She said: “The windows if the helicopter are small, if you have a ditching you need to be able to get out the window.
“If you’re too large, not only can you not get out, the person behind you can’t get out.
“The helicopters are under a lot of strain because of the Super Puma grounding, flights are at a premium.
“If there’s heavy passengers there’s more strain because you can’t have as many people on the chopper.”
The average weight of oil workers has increased by 3st (20kg) in the last 10 years, she said.
In 2005, the Civil Aviation Authority increased the weight allocation for helicopter passengers from 14st (89kg) to 15st 6lb (98kg), meaning more flights have had to be carried out.
She continued: “The increase in average weight of an offshore passenger has resulted in oil companies spending millions of pounds on replacing lifeboats that could no longer accommodate their full capacity.
“Heart attacks are now the greatest cause of death offshore, compared to a few decades ago where it was due to accidents.”
IHS is offering a secret agent themed fitness programme in order to help offshore workers beat the stigma around losing weight.
Those who sign up to the programme, called “Mission 37” after the number of inches their waistline has to reach, work with instructors over a video link.
They are given “missions” every fortnight and are sent secret messages by a dietician dubbed “secret agent C,” and are expected to lose more than a stone.
Ms Martin said: “Mission 37 on the other hand is a secret programme, which doesn’t involve attending any group classes or the need to publicise that you are losing weight.
“Its confidential between the participant and Secret Agent C – our in-house dietitian.”
Those who lose enough with are rewarded with gadgets including mini iPads.
Keith Temple, Rig Manager on the Transocean Prospect said: “People who work offshore are up for challenges.
“Mission 37 offers our people the opportunity to achieve a healthier lifestyle by losing those unwanted pounds and inches.
“The people who have enrolled into Mission 37 will also be trying to outdo their fellow workmates and win this challenge so there will be a fun element attached to this as well.”
But Unite union regional industrial officer Willia Wallace said it was wrong to single out oil workers.
He said: “There is the odd guy that has occasionally been told that they could be doing something about their weight.”
“But we could all probably do with losing a few pounds.”