It's a fact that women undergo major physical changes when they become mothers. Their hormones go haywire, their weight fluctuates and most new moms tend to experience a rather lagging libido when their baby makes an appearance. But what about men?

Recent studies are showing that while men might not carry their offspring physically, they still undergo major physical changes.

Just like women experience a change in hormone production when they have a baby, so do fathers. A study that looked at 624 men showed that new fathers experience as much as one third drop in testosterone levels. This is believed to help reduce a man's aggression and increase his softer, more caring side.

Pack on the pounds

Men don't only become big softies on the inside when they become parents. A poll of 5000 men found that the average dad to be adds a whopping six kilograms to his body weight. The reasoning behind this might be more than sympathy for their pregnant partner and her ever-expanding waistline.

Some theories suggest that like male marmosets that add an extra 20 percent to their body weight, human males might instinctively be storing energy for the upcoming birth.

But they're healthier…

Even though men tend to gain weight when they become new fathers, they're more likely to have healthy hearts. A study published in journal Human Reproduction in the US found that of 135 000 men, those who were not fathers were more likely to die of a heart condition than their daddy counterparts. And the reason for this is simple.

According to Dr Ian Banks of Leeds Metropolitan University, fathers tend to take care of themselves better as they look to the future more. "They change their diet, they give up smoking, they stop going to see their mates at the pub as much," he told the Daily Mail.

He's going through 'pregmancy'

And yes, it's true that some men experience the same symptoms during pregnancy as their partner. In fact, a study of 2000 men showed that as many as one in four men reported experiencing everything from food craving to nausea along with their pregnant partners. This is believed to have a link to the fact that modern men are more involved in their partner's pregnancies.

Men can even experience their own version of the baby blues which doctors think might be due to the drop in testosterone level and that father's tend to feel shut out from the birthing and bonding process.

As men aren't immediately connected to the pregnancy, they often need more time to connect emotionally. "Men get a sudden realisation that everything’s going to be different," Banks explains. He advises women to get their men to talk about how they're feeling during the pregnancy and after the birth.

Dad is an Einstein

Fathers can also claim a little intellectual boost from producing offspring. Scientists believe that the prefrontal cortex — that area responsible for decision-making, planning and memory — improves with fatherhood.

Those women worried about their partners cheating on them are better off if they have a child with their partner. That's because men who have children are less likely to stray — a fact that might be attributable to a father's lowered testosterone level.

But new dads needn't despair, because this drop in testosterone production doesn't last forever — as their children grow up, so a father's testosterone levels will return to normal.