Rex Features
Before I had kids, I had a 30 inch waist and weighed 12st. I'd spend most evenings in the pub – and vowed that's where I would be, smoking a big fat cigar, on the day my wife gave birth, should I ever become a father. My nickname amongst my friends was 'Killer' because of my impetuous personality.
Fast forward 10 years and I barely recognise the man I used to be. I've got a gut a darts player would be proud of; the pub is a Once Every Blue Moon memory – and I find myself crying when kids get booted off the X Factor.
But the biggest surprise of all – to me at least – was where I was the day my first son was born: right there at the business end, like a rugby player at the back of the scrum, ready to catch my baby when he came out.
That's what fatherhood has done to me. Damn you, fatherhood! I'm joking, of course.
I presumed all of these changes were just part of getting older. But according to research, it's fatherhood that mellows us men, not just the ageing process. It's fatherhood that gives us health, empathy and comfort in our own skin. In a nutshell, being a Dad rules! OK?
At the age of 47, and the proud stepdad to a nine year-old girl, and dad to sons, aged seven and four, I thought my newly acquired laidbackness was down to me just getting bored of drinking and arguing after years of doing little else. But no, it's being a parent that has changed me – and changed me for the better at that.
It's all down to how fatherhood influences physical and psychological changes in men, impacting on our hormones, brain power, relationships and exposure to health risks, such as cancer.
The research says that, yes, of course women experience radical changes to their bodies, psychology and health – but men do too.
On the upside, fatherhood:
• Makes us more caring
• Boosts our brains
• Gives us healthier hearts, and
• Makes us more faithful to our partners
But on the downside, it also:
• Causes us to pile on the pounds
• Suffer contraction pains, and
• Suffer from Post Natal Depression
Dr Craig Garfield, assistant professor of paediatrics at Northwestern University, who studied 624 new dads, said: 'We're just beginning to understand the contributions fatherhood makes to men's health. Some research seems to show benefits, while some show risks.'
The driving force behind many of these changes is testosterone – or, rather, a lack of it. According to the Chicago research, the hormone that makes us grunt, fight and go looking for sex subsides by as much as a third when we become dads, causing us to become more touchy-feeling, caring and loyal to our families.
Dr Allan Pacey, a fertility expert at the University of Sheffield, explained: 'A drop in testosterone doesn't make a man more child-friendly, but it switches his priorities to invest in the new infant.'
Of course, not all dads are affected in this way. There will always be those who abuse their wives and leave their kids. But I'm talking about the good dads, that is, the majority of us.
And personally speaking, I would say that once you become a dad, nothing else matters. A guy in the pub spills your pint? You walk away: there are more important things in life.
It's as if the chemistry of your brain changes to weed out the trivial and concentrate on the profound – your children.
But also, according to research by Princeton University, becoming a parent strengthens the connections in the part of the brain that is responsible for planning and memory – the very skills needed by new parents.
And a boost in brain power isn't the only benefit. A study of 135,000 men, published in the US journal Human Reproduction, concluded that those who didn't have children were 17 per cent more likely to die from a heart condition.
Not because they're lonely or unfulfilled without the love and responsibility of kids, you understand, but because dads tend to lead healthier lifestyles.
They change their diet, give up smoking and tend to drink less. But having kids also brings dads into contact with GPs more often, plus they are also more likely to have a wife or partner who pushes them to take their health more seriously, which helps nip in the bud serious diseases, such as cancer.
So what's the downside of all this empathy and understanding? Well, fatherhood can make us a bit porky. But don't blame us – blame our other halves. In a poll of 5,000 men, 40 per cent said they'd put on a stone because their pregnant partners were eating more – so we very supportive men tuck in to make our partners feel better about getting bigger.
But there may be another reason, something which we can't control: our paunches may grow in response to our partners' growing bellies. Scientists who studied male marmoset monkeys found that they gained up to 20 per cent of their bodyweight during their mate's pregnancy. The same may well be true for humans.
In fact, one in four expectant dads said they had experienced many of the pregnancy symptoms experienced by their partners, reporting mood swings, food craving, nausea – and even phantom pregnancy pains.
Dean Beaumont, founder of Daddy Natal, which runs antenatal classes for expectant dads, said: 'Sympathy pains - or Couvade Syndrome to give it its medical term - does certainly seem to be on the increase. I think it's a reflection on our changing society. Dads are more involved in the pregnancy now than they've ever been. This puts them far more in tune with their partners so they share the excitement, worry and anxieties that their partners feel. This brings on some of the chemical changes and symptoms relating to pregnancy including, in extreme cases swollen stomachs i.e. baby bumps.'
But this deeper empathy may also lead to a counter response in terms of Male Postnatal Depression, something that affects as many men as women, according to East Virginia Medical School in the US. The difference is, that men are most likely to experience problems three to six months after the baby's birth because men often work right up until the baby is born and so don't have time to prepare emotionally for the arrival.
The reason for Men's Baby Blues, according to Dean Beaumont, is often guilt. 'Men feel guilty about the trauma of the birth, guilt about not feeling bonded or love for their newborn child, guilt when he has feelings of resentment towards his baby,' he said. 'Expectations on dads is now so much higher to be involved and they feel guility if they can't match up to those expectations.'
And he had this advice: 'Dads need to talk to other dads, they need to spend quality time with their baby and make sure they keep talking to Mum.
'Our classes help dads to understand the changes that will take place after their baby is born, both for themselves and their partners.'
The message is simple: fatherhood changes you. Those changes might be hard to deal with at first, but they will ultimately be for the better. They have been for me.
In your experience, do you think fatherhood changes men?