You eat fat and sugar under stress because they physically make you feel better.

Imagine you are sitting quietly, reading this book after finishing a nice meal. You look up and notice a lion stalking you. Do you: A) Think, how odd, a lion is about to eat me, but rather than react I'll digest my meal or B) Forget about all non-essential activities so mobilize every last bit of energy to run!

Hopefully you chose B. But how does your body switch from resting and relaxing to running so quickly? Because stress activates your fight-or-flight response.

When your brain first notices a lion stalking you it tells your adrenal glands to pump out the stress hormone cortisol. Cortisol signals your fat cells to quickly release energy. Your muscles use this energy to boost the "fight or flight" response. After you've either out run the lion or vanquished it with your trusty spear, your cortisol stays elevated a little while to tell your body to refill its fat stores. Then your cortisol level returns to normal. The way your body gets you to refill fat stores is by making you crave high-energy comfort foods loaded with fat and sugar.

The whole lion related stress event was over quickly because you either escaped the lion or became its dinner. But in the modern world stress never seems to end. We may not face lions anymore, but we do fight a continual stream of worries about mortgages, jobs, traffic, kids, bills, and well, I am sure you have your own list of ferocious worries you could add.

If the stress doesn't end then levels of cortisol stay high, which both does damage and tells your body to keep on storing fat. A lot of women will store this fat in their belly, which puts them at greater risk of heart disease and stroke.

Persistently high cortisol levels, like you would experience under chronic stress, keep telling your body you need to eat to refuel your energy stores. It also spikes the hormone insulin, which controls blood sugar levels and effects your feelings of hunger and fullness.

Stress makes you want to eat and continual stress makes you want to eat continually. So overeating when chronically stressed is biologically driven, you eat when stressed for a reason.

What do you want to eat? Good healthy food? Of course not! You want to eat high energy food to replenish your energy stores and fat and sugar are the high energy foods of choice. If you are under constant stress you'll have a constant desire to eat high-fat and high-carbohydrate food. The likely result is you will eat extra calories and gain weight.

But providing high quality energy isn't the only effect eating fat and sugar has on your body. Eating fat and sugar when you are stressed may be the way your body copes with the sometimes overwhelming stress of modern life.

Physiologist Mary Dallman at the University of California, San Francisco, says fat and sugar calm the brain, lowering levels of stress hormones. "That’s why we call them comfort foods," she says. Eating comfort food switches off stress by calming down brain systems linked to anxiety. It's like a little mini-tranquilizer.

If the temptation to eat junk food wasn't already enough, stress hormones may turn on your brain's reward centers so in times of stress comfort foods will taste better, making you eat more of them. Clearly your body wants you to eat high-energy foods in response to stress. You don't have to make up reasons why you like comfort foods, there are good physical reasons for why you crave comfort foods when stressed.

One study in rats showed a hormone called CRF, a hormone humans also release under stress, tripled their desire for sugar. University of Michigan psychology professor Kent Berridge, who worked on the study, says:

People who feel bad during stress cope in part by overeating or pursuing other incentives. It turns out a stress chemical also activates the same brain mechanism that goes wrong in drug addiction to make us excessively want pleasurable things. This could trap individuals into chasing incentives they could normally resist, pulled in by tempting cues or images that become more powerfully wanted.

In other words, you might normally be able resists that delicious double scoop of your favorite ice cream cone, but when you're under stress just seeing a glossy color picture of a cone might make it irresistible.

While stress effects us all, women may have a harder time with stress. A study conducted by researchers at Rush University Medical Center in Chicago and the University of Pittsburgh has found that stress can lead to weight gain in women. "Under stress, people conserve more fat, and we think that is perhaps what's going on here." says the study's lead author, Dr. Tene T, Lewis. Women who reported more negative life events (such as the death of a relative, loss of a job or divorce) at the beginning of the study were more likely to gain weight.

Try not to let this bother you, but your stress over weight loss may cause a cycle of weight gain. The cycle goes something like this: losing weight is literally stressful; the Beat the Diet Game stress hormones then make you crave fat and sugar so you'll feel better; eating more fat and sugar cause you to gain weight; you try harder to lose weight. And the cycle starts all over again.

Isn't it amazing how our ancient survival instincts for dealing with lions can be so wrong in our modern environment? Fortunately there are other ways of dealing with stress. We'll talk about some options in later strategies.