Excerpt: 'You: Being Beautiful' on the Biology of Sex Read an excerpt of Dr. Oz's book that delves into the biology of sex.

March 9, 2009  -- In the book he co-wrote with Michael Roizen, Dr. Mehmet Oz takes a look at beauty in all its aspects.

"You: Being Beautiful" is an "owners manual" to discovering inner and outer beauty and lends advice for work, love and life.

In the excerpt below, Oz takes a look at the biology of sex and the scientific side of what gets men and women all hot and bothered.

Read an excerpt of the book below and then click here to read more from the "GMA" Library.

The Biology of Sex

Humans are the most sexual species around. How do we know? (The answer is not from National Geographic specials.) One example: Women are sexually active for almost their entire lives and throughout all times of their menstrual cycle— meaning that they can choose to have sex even during times when they are physiologically unable to produce offspring. That means that sex must have some higher purpose and function than simply reproduction. Another: Sex drive does not need to decrease with age, meaning that we strongly desire the physical connection even after we're unable to bear children.

What's that higher purpose? For one, sex can serve as that nirvana moment between couples—a time when you feel complete happiness and intimacy, a time when you express your love to your mate. In other words, sex is designed to make you feel good. Real, real good. How good? For starters, consider that:

Men who have sex three times a week can decrease their risk of heart attack and stroke by 50 percent.

Women who enjoy sex tend to live longer than those who don't.

Great sex makes your body feel and be the equivalent of two to eight years younger—same for men who have 150 to 350 orgasms a year, compared to the average of once per week.

Having orgasms seems also to help decrease general pain.

Increasing sex from once a month to once a week, according to researchers, is the happiness equivalent of an additional $50,000 in income for the typical American.

It's also interesting to look at the gender-based evolutionary functions of sex.

Thousands of years ago, the woman felt that it was her job to grow the species and raise the children, so she needed someone who could protect the family. Her body responded better to intimacy (she provided that intimacy so that men could help her reach orgasm). A man had different intentions.

When he saw a bunch of marauders marching through camp, he would get aroused by the threat to his family and mate—a signal that his sperm needed to beat out other men's sperm.

So a man responds sexually to anxiety, risk, and excitement, in contrast to a woman's desire for intimacy.

That hard-wired difference is one way to explain the different ways that men and women feel aroused—and it's the basis for helping you figure out how to better mesh the sexual preferences and differences in your own relationships so that you don't only go through the motions when it comes to sex but also experience the emotions.

While you may think that the biggest sex organ of all is one that's covered up by the latest style from Jockey or Victoria's Secret, your brain is actually your biggest sex organ. Some researchers have said that sexual thoughts, for example, go through a man's brain once every 52 seconds and through a woman's only once a day. And even conservative researchers say that men have many more sexual thoughts than women do.

Perhaps that's because men have 2.5 times the amount of brain space devoted to sexual drive that women do (or because women have more important things to think about).

Sex, of course, is more than just thinking about it; it's also about craving it. That craving originates in a part of the brain called the insula. Blocking messages to the insula is one of the ways that cigarette cessation techniques work—good news for many, they don't block sexual craving messages; in fact, bupropion, the drug we most often use in our breathe-free program with nicotine, actually increases libido in most people. The insula (remember it from chapter 8?), a primitive area of the brain, is especially active in women who have more frequent orgasms.

Let's now look at the way men and women biologically work when it come to sex:

WOMEN: During sex, your pupils dilate, nostrils flare, heart rate increases, oxytocin level increases, sweat glands open for cooling, breasts enlarge by 25 percent, and nipples increase in height by half an inch. Infrared cameras also show increased blood flow to the lips, nose, and labia. All of these things happen as the sexual stimuli build up to the almighty orgasm (see Figure 10.3).

A good question to ask right about now: Why do women have orgasms?

Evolutionarily, it was one of the ways that women could tell whether a man would be a good lifelong partner, because it could help women distinguish between a caring, patient male and a selfish or impatient one. Nevertheless, female orgasm can be so subtle that some women don't even know when they've had one.

Here's what happens:

During intercourse, your vaginal walls make fluids that let your partner's penis slide with just the right amount of friction. Together with the sights, sounds, and smells of sex, the stimulation to the clitoris, labia, and breasts all builds up a crescendo of intense physical sensation.

This is about the time when your brain tells your vagina and nearby muscles to contract. Why? To bring his penis in deeper and increase the chance of his sperm hitting its target—the egg.

In the process, some women even ejaculate. During orgasm, the uterus dips in like an anteater and sucks up the semen into the uterus to further increase the chance of fertilization.

The female orgasm also causes hormones to increase contractions in the vagina and uterus and help move semen into the uterus (women who orgasm between 1 minute before and 45 minutes after their partner's ejaculation have a higher tendency to retain sperm compared to those who don't have an orgasm).

The female orgasm, of course, isn't an easy thing to describe.

The brain serves as the main conductor in this symphony, but it might involve many different instruments, sometimes including the area known as the G-spot, which is parallel to a gathering of nerves on the male prostate.

Women usually do not have a single spot like some magic sex-me- here button but rather a region of nerves like those spread over the surface of the male prostate. That's because as a woman's reproductive organs develop in utero, her rudimentary prostate moves away so these nerves end up on the vaginal wall. So if you insert your index finger upward into the vagina and make the "come here" movement, you will touch the G-spot region that exists in some women.

The region is often not that sensitive either, but you never know until you try. The fact that women can be stimulated to orgasm through not only the genitals but also the mouth, nipples, and other parts of the body points to the complexity of the system—and reinforces the fact that the true biology of sex really evolves within the brain. (One theory is that sexual stimuli are carried from the cervix and uterus to the brain through the vagus nerve—one of the nerves stimulated during deep breathing and meditation.)

MEN: If you allow us a few moments to talk about the male anatomy, we think you'll be pretty amazed.

Biologically, men's sexual organs are much different than those of other species. For one, a man's penis doesn't have a bone, unlike those of other species. Why? The bone makes for easy and fast access for males in the animal kingdom (to inseminate their partners quickly); men give up the bone but gain a disproportionately large penis for their body size in return.

The evolutionary implications: One, men use the penis as a tool of attraction, implying that women do place some value in using it as a diagnostic for evaluating potential mates (not so overtly these days). And two, the lack of bone implies that men do equate emotions with sex, since they must be aroused for an erection; instead of easy and fast access, which can be painful to the females, it takes more care to have a sexual relationship between two people.

Another interesting observation: Humans have proportionally smaller testicles than males in other species; that's because other species need to ejaculate more semen to fertilize partners who are in heat prior to other males of the tribe and ensure propagation of their genes.

Human males don't need the size because of the biological drive to be monogamous (at least serially).

Now, it doesn't take a sexologist to know the purpose of the male orgasm: Find the egg, fertilize the egg, begin shopping for Barbies. But what's interesting is that this mad dash to the egg isn't some New York City marathon where all the starter sperm strap on their Nikes with the goal of making it to the finish line. Some of the sperm do that, but others are more like defensive linemen. Their job: to stop other men's sperm from scoring.

Some sperm even have a dual role—blocking other sperm but allowing their own sperm with their genes to penetrate more effectively.

Now, during a man's orgasm, the brain is firing like a lit-up pinball machine, causing contractions in most muscles of the body. The purpose: Like a woman's, these contractions help increase the chance of pregnancy by enabling the penis to penetrate as deeply as possible. The glands that make semen, mostly the prostate, squeeze repeatedly, propelling sperm as deep and as far as possible. The prostate, by the way, is often referred to as the male G-spot, because it's made up of some of the same types of tissues as some of the spots identified around the nerve plexus that is the G-spot in women and can be stimulated in a similar fashion by some adventuresome couples.

Normally, ejaculation cannons semen forward through a man's urethra and out the tip of his penis. Semen, by the way, contains hormones like oxytocin that also have a feel-good effect on women. The reason ejaculation never gets mixed up with urine is that there's a tiny muscle at the entrance of the bladder that prevents semen from slipping backward or urine from propelling forward during orgasm (it's a roadblock of sorts, so the only way for the semen to go is out). Now, some men suffer from what's called retrograde ejaculation, in which that tiny muscle doesn't work right, causing semen to backtrack into the bladder rather than to the promised land (causes for this include some side effects of surgery or medication).

Retrograde ejaculation doesn't affect a man's ability to achieve an erection or ejaculate, but it may affect his fertility.

The opposite of retrograde ejaculation, of course, is when semen shoots out faster than a round from an Uzi—something that can cause angst in men and stop a satisfying sex session in its tracks. Premature ejaculation can be caused by a number of things, including medication, hormonal changes, high blood pressure, and stress.*

One of the other causes—an enlarged prostate. Since the prostate generates 95 percent of the substance that comes out during ejaculation, it's no wonder that it has a lot to say about what comes out and when. Since an enlarged prostate gets more stimulation during sex, the friction can stimulate orgasm— leading a man to ejaculate whether he wants to or not.

* Premature ejaculation affects one-third of men. Some treatment options include antidepressant medications (SSRIs) and behavioral techniques. Some docs suggest the man masturbate an hour or two before sex to help delay ejaculation during sex. Another technique is called the squeeze technique, in which the woman squeezes the penis at the point where the head meets the shaft for several seconds, right before a man feels like he's going to ejaculate. That should help delay orgasm; wait 30 seconds, then continue.

YOU Tips!

Try Tantric. When you hear the term tantric sex, you may assume that we're talking about the ability to have a sexual interlude that lasts longer than a transcontinental flight. But that's not really the goal of tantric sex.

The goal stems from the desire and ability to have more of a physical and spiritual connection during sex. Physically, for men, that means developing the ability to, as tantrics say, "retain the seed"—that is, having the ability to control ejaculation to allow sexual energy to flow. But the essence of that practice—and of the tactics below—is really about mindfulness, or being deeply aware of yourself, your partner, your life, and what's called the sacred life force.

These tips can help you maximize your sexual experience—and bring deeper emotional levels to your relationship.

Change your mind-set: Stop thinking that your sexual satisfaction is the responsibility of your partner. We're all responsible for our own experience. Be open to discussions about sex with your partner, and be open in exploring your own body to help your partner help you.

Men, when you're by yourself, you can practice increasing your sexual energy. Bring yourself to two or three peaks at a time—ejaculating only after you've come close to the edge a few times. (Deep breathing can help you teeter on the edge without falling over.) What you're doing is priming your prostate gland like a pump to help improve sexual performance.

Challenge yourself. You give yourself goals at work and in life, so why not create some for the bedroom? It can be anything—practicing Kegel exercises during the day or working to locate your G-spot if you haven't.

Be softer. One of the main tenets here is to slow things down. Don't be in such a rush to get to bed or to finish up. Carve out time to have a marathon lovemaking session in which the final goal isn't necessarily an orgasm but simply the journey itself.

Play to Your Partner's Strengths

We all know the whole Mars and Venus debate. Men are different sexual creatures than women. Men respond to new visual cues; women respond to friendly emotional ones. Go a little deeper, and you understand that it's more that men respond to fear and excitement, and women respond to intimacy.

Instead of agreeing to disagree, couples should capitalize on their differences to help make their partners more comfortable in bed. So what does that mean? A man should make it a habit to look into his partner's eyes during sex: That eye lock is a way to increase intimacy (and oxytocin). And a woman should acknowledge that her partner's arousal may be based more on urgency, meaning that it's not so bad to have the lights on during sex, crave a quickie, or meet up for a lunch hour that involves absolutely no lunch at all.

Go Crazy

There's a reason why bungee jumping, river rafting, and sneaking into the supply closet can make the perfect first date. Doing novel things with another person stimulates dopamine—the feel-good chemical that's elevated when you're in love.

Also, since men are aroused by fear and anxiety and heart rates are elevated during both attraction and danger, it increases the likelihood that a man will find his partner more attractive during a daredevil date. The dopamine is actually firing high when you first get together but not necessarily on the 80th date, so it's even better to make special new adventures or variations more common the longer you're together.

Novel choices are especially great for couples whose libido has diminished or whose sex life has gone stale.

Mix it Up

Guys, listen up. While men have orgasms in 95 percent of sexual encounters, some reports have women having orgasms in 69 percent of encounters. * Interestingly, the more varied the sexual activity, the more likely a woman is to have an orgasm.

* We couldn't have made up a better number for this statistic if we tried, eh? Of course, getting these numbers is hard to do, and some reports have much lower numbers.

That means mixing it up among manual, oral, and genital stimulation. Oral sex, by the way, increases a woman's chance of having an orgasm.

Open the Fridge

While you're probably thinking that we're going to tell you to get some chocolate sauce and whipped cream, the truth is that food plays a vital role in our sexual desire—some because of the smell, some because of the shape, and some because they alter your body chemistry to make you a more desirable mate.

Our choices:

Take advantage of pheromones: Capitalize on those scents by exposing yourself to them: Research shows that the scents of lemons, doughnuts, and licorice increase penile blood flow (necessary for men to achieve an erection).

Don't eat the doughnuts (that slows blood flow dilation down); just smell. For women, it's licorice and cucumbers.

Why? For women, the phallic shape subconsciously plays a large part in that. Another good one to smell for its pheromone effect: baby powder. It makes the female partner think of the evolutionary goal of sex, at least subconsciously.

Strengthen the sperm: If your goal is to consummate your attraction with reproduction, then you should also supplement yourself with zinc, selenium, folic acid, and vitamins C and E, which have been shown to increase sperm count. But most important is DHA-omega- 3 fats—the active ingredient in fish oil that can be obtained in even more purified form from the algae they eat.

Go back to that sauce: Chocolate has long been considered a love drug, because some of the ingredients* have a feel-good effect.

One study also shows that caffeine may have a positive effect on female libido.

Get Your Drive Back

If you feel as if you've lost some of your sex drive, try these tactics for restoring some of your long-lost libido:

Check out our battery of tests from chapter 6. A change in hormones or energy levels could be a primary driver.

Ask yourself what happened in your relationship when you noticed your sex drive changing. If you can ID the out-of-bed problem, it can help lead to an in-bed solution.

If you're suffering from some kind of vaginal pain (see chapter 7), some strengthening exercises (called Kegels) may help, depending on the issue.

Experiment with more oral sex, fantasies, or watching each other in videos or in real life.

Change things up to charge things up.

Phenylethylamine, tryptophan, and anandamide.

Get comfortable with yourself. You can try to reboot your system by experimenting with your body and finding what brings you joy (for instance, many women like the shaft of their clitorises stimulated, rather than the tip, so you need to be able to communicate that to your partner). Get comfortable with the fact that a mirror, sex toys, and locked doors can be a healthy part of a solo experience that can energize your sex life with your partner.

Check Your Waist

Fat doesn't just make it hard for you to see your organs. It also makes it hard for them to function, which is why increasing waist size means decreasing libido. One of the reasons why men lose libido: omental fat (fat around the belly). That omental fat converts testosterone to estrogen and thus diminishes sex drive.

So if you're experiencing a loss of sex drive, a doc may first check the size of your testes (they should be roughly a ratio of 11/2 inches height to 1 inch width, or three finger widths by two finger widths). If they're normal size, it could mean that omental fat is causing the testosterone drop. While you're losing the belly fat, a medication called clomiphene, which blocks the conversion from testosterone to estrogen, may help.

If you want to keep your libido (or get it back), get your waist size to less than half your height.

Go All Lombardi on Him

When it comes to sex, some women are as silent as a 1920s movie. They fear that they can't tell their men what they want in bed—maybe because they're shy, maybe because they're embarrassed, or maybe because their partner's ego is as delicate as a silk blouse.

But the best thing you can do with your mouth to improve your sex life has nothing to do with the X-rated thoughts crossing your mind right about now; it's talking.

Women need to teach, coach, and encourage their men to give them what they want—and how they want it. Believe us, it's much more of an ego boost for men to know they're pleasing their women than not to know something was wrong in the first place.

Keep It Pumping

Good sex isn't just about blindfolds and finger paints. It's really about good blood flow.

That ensures you're getting the right nutrients to your brain, as well as the right stimuli to your sex organs. So improving your sex life means avoiding the things that decrease blood flow (nicotine, drugs, saturated fat, trans fats, sugar, syrups, diabetes, high BP) and embracing the things that increase blood flow (exercise, avocados, fruits, vegetables, 100 percent whole grains, ginseng, ginkgo biloba, l-arginine, lemon, citriulline).