Piling on the pounds will push up the premiums when you apply for life or critical illness cover. New insurance customers will find the notch on their belt that was acceptable three or four years ago would now mark them out as obese - with a 50% or greater premium addition as insurers try to catch up on the obesity explosion.
But even if policyholders manage to shed weight later on, insurers may not slim down monthly payments in line.
Obesity rates have risen threefold in the UK over the past generation and seem set to expand far faster over the next 25 years on present estimates, potentially hitting insurance profits.
Obese people are more prone to heart disease, strokes, high blood pressure, diabetes, chronic depression and many other life threatening conditions.
The key obesity measure is BMI - Body Mass Index. The BMI compares weight with height, irrespective of sex. To calculate it, divide your weight in kilos by your height in metres squared.
If the result is less than 19, you are probably supermodel thin and unhealthy. A 19 to 25 figure is normal; from 26 to 30 is overweight but not too much, from 30 to 40 is obese and anything above is extreme.
To save you doing the sums, a 5ft 2in person weighing up to 9st 5lb is "normal"; and up to 11st 4lb is overweight (and above that, obese). A 5ft 6in person can weigh up to 10st 8lb normally; and up to 12st 11lb overweight. A 6ft person is normal up to 12st 9lb; overweight up to 15st 3lb. Beyond these figures, obesity starts. Extreme obesity for a 5ft 9in person would be from 19st 3lb upwards.
But now insurers are increasingly considering people within the overweight parameters as obese.
Critics of BMI say it does not reflect different body frame sizes. They say many athletes - especially rugby players and rowers - would be treated as unhealthy. They say waist size (up to 40 inches for a man or 35 for a woman) is a better indicator. But, for the moment at least, those arguments are academic.
"It is true that BMI is not universally accepted as an obesity measure. But that really does not matter, as all insurers currently rely upon it," says Kevin Carr at brokers LifeSearch.
"What is important is that insurers are continually moving the line between normal and obese downwards. This means they can charge more for people who previously would have been insured for life cover or critical illness at normal rates," he says.
Headline premiums for life and critical illness policies have fallen dramatically over the past 20 years since the Aids/HIV panic forced up rates. And they continue to fall. But that masks far more careful underwriting by life insurers.
"Application forms are getting longer as underwriters ask more searching questions," says Mr Carr. "They are cherry-picking the fittest people on their standard rates but adding on a lot more in additional premiums for those who tip the scales too far."
According to LifeSearch, insurers were happy to provide life cover four years ago for someone with a BMI of up to 33 - a 5ft 6in person weighing 14st 8lb. Now, they see a BMI of 28 as borderline - the same 5ft 6in person can now weigh no more than 12st 5lb if they are not to be hit by a policy loading with some companies.
"We're no longer talking noticeably fat or even very stout. But the other factor is the old loading for obesity meant premiums jumped up by 20% - now we're talking 50% or more. And while insurers will sometimes reduce the loading for some medical conditions if they appear cured or in complete remission, removal of loading for obesity is very unlikely," Mr Carr warns.
"Critical illness policies are now being written with tighter definitions to cut out some medical conditions which previously gave rise to a claim. Selection is more stringent."
However, some in the insurance industry are more upbeat about obesity. While they recognise that fatness is replacing fitness for many, and the need to select customers more carefully than before, they hope that the main effects of obesity happen to those outside their policyholder base.
"There is no denying the fact that you see more obese people. But the life industry is still seeing an improvement in mortality trends," says Tony Jupp, Norwich Union's chief life underwriter.
"What seems to be happening is that the section of the population which buys the bulk of life insurance plans seems to take care of their weight, fitness and health while the other half carries on getting fatter. It depends whether you look at the population as a whole or those with policies," he says. "It is a question of social class, with our customers not putting on as much weight as the national average."
Norwich Union also believes it will escape being hit with an unexpected wave of life and critical illness claims. It says: "Most problems arise when the policies have expired. People may be at risk of premature death but if that means they die at 75 instead of 80, it will have little effect on our claims and on future premiums," Mr Jupp adds. "Although we do not underestimate the problem, earlier than expected death is not yet a trend in our policyholder portfolio.
"In addition, there is always the hope that medical science will come up with a way to reduce or cure obesity. That way, we can take people on at normal rates with a BMI of up to around 30, balancing the worry that some will go to 35 or even 40, where obesity will really impact, against the chances of an anti-fat pill. Most people naturally increase their BMI as they age, we have to hope it will be within acceptable parameters."
But Mr Jupp, whose views reflect most other life underwriters, is realistic. "We also look at our new potential customers and reject more than we used to, or only take them on with 20% to 50% loadings. That way we either cut out future risks or make more money out of them to match the chance of a claim. We are keeping a close eye on the trends."
The food to steer clear of
Motor insurers could soon be asking what you eat as well as what you drive.
According to new research from the RAC, bad dietary habits leave motorists feeling tired at the wheel, posing a risk to their and other road users' safety.
"Most motorists fail to consider the detrimental effect of poor quality food on their driving, especially on long journeys" says dietician Sian Porter. "Choosing more carefully can significantly improve safety.
She says drivers should avoid high sugar foods such as sweets. The initial rise in blood sugar is followed by a quick drop leading to tiredness, hunger and low concentration.
They should also cut out high fat foods such as burgers (some also high in sugar) and chips. These foods go through digestive systems quickly leaving drivers feeling dizzy and sick.
"Feeding these to children can also lead to tears and tantrums," she adds. "Drivers and passengers should opt for healthy choices and small, regular meals rather than a blow-out."
Motor insurer More Th>n says the number of factors it looks at is growing.
"We would certainly consider anything which could help promote safer driving," it says.
Gym and tonic in the battle for fitness
Fight the flab with free gym membership - that's the deal on offer from a private medical insurer.
And if you follow our guide carefully, you can get Holmes Place and Cannons' membership plus health insurance cover for around half the standard membership fee for the gym alone.
The deal comes from PruHealth, a partnership between Prudential and South African medical insurer Discovery Holdings. It says it helps it wants to help combat obesity - as well as help recruit policyholders.
New customers of PruHealth are given six months' free membership at Cannons or Holmes Place. It has arrangements with other clubs in areas where these two are not convenient.
To get the best out of the arrangement, policyholders should opt for paying the first £1,000 of any claim. This lowers the premium as, in practice, the high excess means few claims.
A 40-year-old woman with no previous medical history living near London would pay £29 a month for the £1,000 excess policy plus the free gym membership, worth £60 a month. After six months, she can cancel the PruHealth policy and the gym membership without penalty.
PruHealth buys gym passes in bulk, paying a third of the normal price.
"We first ran this offer in the new year - a peak time for joining health clubs but poor for insurance sales. Around half switched from other insurers; and the others were unashamedly attracted by the free health club," says PruHealth chief executive Shaun Matisonn.
The company repeated the offer online in September and intends to do so again next January. But any new customer phoning the firm and mentioning the free gym offer will get the deal.
Beyond the obvious incentive, there is a serious point. "We see obesity as a lifestyle issue in most cases. By offering lower insurance premiums for continuing fitness plus cut price or free gym memberships, we help create wellness. It's a focus on the inputs - healthy diet and sensible exercise leading to a better future - rather than concentrating on an unhealthy person and punishing them via heavy premiums," Mr Matisonn adds.
