You probably believe men think about sex every seven seconds. But that would mean men are thinking about sex more than 6,000 times a day, or pretty much every time they take a breath.
That would not only drive most people mad, it would make them incapable of performing any other functions at all. However, it's true research data suggests men think about sex more than women do. A comprehensive study on the subject was published in 1994.
More than half of men reported thinking about sex every day or several times a day, versus only 19 per cent of women.
Just over 40 per cent of men reported thinking about sex a few times a month or a few times a week, versus 67 per cent of women.
Only 4 per cent of men said they think about sex less than once a month, versus 14 per cent of women. So, yes, men think about sex more than women, but the difference is far less dramatic than you might think.
Almost half of men don't think about sex every day - and that's a far cry from the way they are frequently portrayed.
2. MEN PEAK AT 18, WOMEN AT 28
We've both heard this myth so many times we assumed it must be true. But is there any scientific basis for this?
Certainly men's testosterone level peaks at around age 18, while women's oestrogen levels peak in their mid-20s.
Since low hormone levels have been associated with lower sexual drive, some have asserted the opposite must be true: when your levels are at their highest, your drive must be at its peak.
Common sense tells us sexual desire fluctuates constantly, and is related to far more factors than age
But what does 'peak' mean? If we believe frequency of sex is what matters most, single men are most likely to have sex four or more times a week in their 30s, and for men with partners, this is most likely in their 40s.
For single women and women in relationships, such frequent sex is most likely in their late 20s. So if this is the standard we use, men are peaking after women. Common sense tells us sexual desire fluctuates constantly, and is related to far more factors than age.
Sounds plausible, doesn't it? But unless you are having sex for much longer and with much more vigour than the average person, sex is probably not going to get you anywhere near the recommended amount of exercise to lose weight.
Sex is considered to be only a mild to moderate intensity activity, and the average sexual encounter lasts only around five minutes. Estimates of how many calories are used up range from 25 to 125 - not a great deal.
4. TESTICLES SAG WITH AGE
Most men think so. And the male reproductive tract definitely goes through a number of changes with age - the testicles produce fewer sperm, slower sperm, and sperm that are less able to fertilise an egg. The components of the testicles also start to change.
The tiny tubes where sperm are produced start to degenerate, and, overall, testicles also become smaller. These smaller testicles may seem to be hanging lower, but this is because the sac is a bit emptier.
But while it's true there might be some weakening of the skin of the scrotal sac, the smooth muscle that controls the movement of the scrotal sac up and down continues to function for life. And that kind of muscle - smooth muscle- is unlikely to sag very much.
5. SEX BEFORE SPORT IS BAD
Many athletes are told they should not have sex the night before a big game because they will have less strength, less concentration, or not enough testosterone to fuel an aggressive, strong performance.
In fact, the science of what happens in the body during and after sex suggests athletes might actually perform better if they did have sex. In one study, men who had sex the night before a sporting event had higher testosterone levels the next day than those who had not had sex.
Sex has also been shown to have no impact on leg muscle strength, grip strength, reaction time or flexibility.
6. BIG FEET, BIG PENIS!
Many people think you can size up what a man's penis is like by looking at his feet, hands, or nose.
Interestingly enough, the connection between big feet and big penises has some roots in science.
A gene called the Hox gene plays a role in the development of the toes and fingers, as well as the penis and clitoris. If the same gene controls the growth of toes, fingers, and penises, then might it make all of them grow big (or not)?
In fact, there's no good evidence that men with big feet have bigger penises. A study of 63 men in Canada did find a weak relationship between the length of the penis and shoe size, as well as a correlation between penis length and height.
However, it didn't actually measure the men's feet, and relied on their reported shoe size. In contrast, a slightly larger study that looked at penile length and shoe size for 104 men found no correlation.
These are pretty mixed results; one study says the two are weakly connected, the other says that they are not. And they are both small studies.
Our conclusion? You can look at a man's feet all you want, but it's only going to give you an idea about his taste in shoes.
7. SEX IS BAD FOR A DODGY TICKER
Everyone has heard horror stories of people dying of a heart attack in the middle of sex, and those with a history of heart disease may be particularly afraid that sex is too much for their heart. But the chance of having a heart attack during sex is very low.
A large study called the Framingham Heart Study tells us that if you are a man who doesn't have diabetes and doesn't smoke, the chance is just one in a million.
And while people who've had a heart attack do need to exercise some caution when resuming normal activities, they do not need to be so afraid of having sex.
The truth is that most people just don't exert themselves that much during sex. The physical exertion is similar to walking up two flights of stairs. So if you can do the treadmill test (the stress test used to check heart function), this is about the same level of exertion you'd have during sex that produces an orgasm. During this test, patients walk on a treadmill, with its speed or slope gradually increasing, while the heart is monitored.
Two major reviews of all related studies found no evidence of weight gain
8. THE PILL WILL MAKE YOU FAT
Nearly all medications have side-effects. But it is a myth that the Pill causes weight gain.
It wasn't always the case - when it was first developed, the Pill had very high levels of oestrogen and progestin - a synthetic version of the hormone progersterone - which might have caused weight gain.
But today's Pill contains much lower levels of hormones, and two major reviews of all the studies found no evidence of weight gain.
9. OYSTERS ARE APHRODISIACS
For millennia, human beings have believed that certain types of food or drink lead to arousal.
Oysters have been a favourite aphrodisiac since Greek mythology featured Aphrodite, the goddess of love, emerging on an oyster shell. Casanova was rumoured to eat 50 oysters every morning to fuel his crazy sexcapades.
But no study has ever shown oysters have a sexually enhancing effect. Nor can scientists find any special ingredient that would suggest an ability to turn men or women into raging beasts.
Oysters are mostly water, a few carbohydrates, and some minerals. They do contain a lot of zinc, which sperm need to be healthy, but otherwise there's no secret sexual ingredient in the oyster.
What about chocolate? There's no doubt chocolate is a magnificent substance. It contains a lot of compounds called flavonoids, and flavonoids in general have antioxidant properties, which are good for the body.
Several studies have linked chocolate to lower blood pressure and better functioning of blood vessels. Cocoa also increases nitric oxide in the bloodstream, which creates the kind of dilation of blood vessels needed for a man to have an erection.
Lower blood pressure and better working of the blood vessels might have a positive effect on the male sexual equipment. Chocolate has another effect that might be stretched into an aphrodisiac.
It can stimulate a small release of phenylethylamine and serotonin, natural chemicals that boost our mood. And people who are in better moods may want to have more sex!
But there is no scientific evidence linking any one food to enhanced sexual desire or pleasure.
As for plants and herbs, there is quite a collection of studies looking at what has been used to help with sex over the years. Quite a number of the plant compounds did improve sexual activity - in rats. For example, flowering plant curculigo orchioides increased rat penile erections and rat penis weight, while litsea chinensis, a type of laurel, also increased penile erections.
But only one of the 41 plants studied was tested on humans, where it had no significant effect
Dr Carroll is a professor of paediatrics at the Indiana University School of Medicine, where Rachel Vreeman is an assistant professor of paediatrics.
