Hardcore crash dieters are probably familiar with this phenomenon. They diet stringently, purging all unnecessary calories, for a few days. Maybe even a week or two.
Then, suddenly, appetite becomes overwhelming and the dieters lose control. They binge on whatever they can get their hands on: a bucket of chicken, an econo-size bag of cookies, or what the hell, a block of Crisco. They feel like the biggest, most out of control pig in the world, and indeed they have temporarily lost control of their eating behaviour.
Frequently this triggers a downward spiral of more bingeing, or another attempt at dieting that ends in another binge. The cycle continues. Usually this results in an increasingly diminished self-image and a gain in bodyfat.
Why does this happen? Another component of the starvation response is a reaction from the hormones that control appetite, hunger and satiety.
Appetite is an interest in eating. We can have an appetite even when we do not really require food.
For example, after a full meal, we can usually find room for dessert. Or, we can be hungry even though our caloric requirements have been met. This tends to happen especially with a diet high in refined carbohydrates (sugars and starches). We can eat/drink 3000 calories in sugary foods and still be starving, whereas if we ate 3000 calories in roast beef and brown rice, we’d be pretty stuffed.
Alternately, we can be physically hungry but not interested in eating anything we have in the fridge. Hunger is a physical state of the body asking for food. Our tummy rumbles and maybe hurts a little, we may feel lightheaded, we may be grumpy. Physical hunger does not always correlate with appetite.
Satiety is the degree of fullness or satisfaction experienced after eating. This is controlled by a number of factors, such as the sense of the stomach expanding (which is why high-volume foods like vegetables often fill you up better), the coordination between brain and gut, and the release of hormones as food is consumed.
The many hormones that control appetite, hunger, and satiety respond rapidly to changes in psychological and physiological states. Their interactions are complex, and they work in conjunction with other metabolic functions such as sleep/alertness, heart rate, and so forth.
For example, a group of hormones known as orexins are involved in both appetite regulation and sleep-wakefulness. Mice whose response to orexins is disrupted (either by administering additional amounts of the hormones, or by genetically altering their response to them) demonstrate significant differences in both their appetite and ability to stay awake.
They can make narcoleptic mice! How cool is that?
This is one reason why any appetite hormone-altering drugs, including substances as benign as caffeine, must be used with caution. If one part is affected, the whole system is affected.
When calories are reduced, as in a diet, the body reacts.
Within hours, hormone levels can begin to change and respond. The brain is very sensitive to changes in these levels, and will begin to send signals that it would like more food, please. By the way, damage to certain parts of the brain, such as the hypothalamus, will also result in disrupted appetite. Disrupted appetite (either under or overfeeding) can in fact signal an underlying medical condition.
In the short term, no big deal. Indeed, if you are working on gradually reducing your intake in a healthy and sane way, you may notice some low levels of hunger, which are quite normal.
In the long term, though, if you keep on truckin’ with severe restriction (especially if that restriction is accompanied by other physical, mental, or emotional stressors — including heavy training, ladies), then you’re setting yourself up for some fun times.
You see, appetite can also be affected by conditions such as acute stress. You may have noticed that you’re not very hungry when you’re tense, or that your response to stress is to eat more. In both cases, your body is responding to elevated levels of stress hormones.
Elevated stress hormones, such as cortisol, can also increase body fat deposition. Under stress, the body thinks it needs blood sugar to deal with fight or flight, so it cranks up some blood sugar-releasing activity. Whoo! Now you’ve got a depressed metabolism but plenty o’ glucose roaming around in your veins. (If your car’s got a flat, no worries — you just created yourself a nice spare tire.)
It gets even better. Cortisol can disrupt your sleep. And so can adrenaline. When the body runs low on cortisol, it goes with Plan B: adrenaline. Adrenaline is the big red emergency lever for blood sugar release. When the body yanks down that lever, you get a blast of glucose and a little kick in the pants. Which makes you more stressed. Which makes your sleep worse. Which — ta da! — makes your blood sugar regulation worse too.
Meanwhile, under stress, your sex hormone production declines. Your “young woman” estrogen (estradiol) declines, and the body gears up production of the “problem” estrogen (estrone). Thing is, much of our estrone comes from body fat… in our midsection. Menopausal women start to collect fat around their middles because of such hormonal shifts. It’s the body’s way of attempting to replenish a dwindling estradiol supply. So, when ovarian production runs low (whether because of normal aging or because of the brain saying “Shut ‘er down, girls, we’re too starved to get knocked up!”), the body often puts on midsection fat to compensate. Now, not only will you struggle to button up your pants, but estrone in excess can have negative effects, such as increasing your risk for certain cancers (which is why obesity is correlated with many hormonally-related cancers). Plus, thanks to having less estradiol on top of low blood sugar, you’re moody as shit, can’t concentrate, and aren’t interested in getting jiggy.
So you’re sleep-deprived, full of glucose, moving towards insulin resistance, hormonally menopausal, and nurturing a new set of love handles. Oh yeah, you’re cold too, because your thyroid is downregulating its production.
By now, if you’ve kept these shenanigans up long enough, you’re miserable and hate all life on the planet.
Because you feel like shit, you might even reach for some caffeine to feel better… which gives you another adrenaline hit, increases your stress more, and makes you more likely to grab something sugary to take the edge off when your blood sugar plummets an hour later.
It’s a nasty, nasty cycle.
Anyway, so when calories are reduced suddenly and significantly over a longer period, say a few days or longer, the body really starts to kick in with the anti-starvation hormone response. This response is intended to force you to eat, as well as to conserve what energy is left.
As a result, you may feel sluggish and hungry. You may start thinking about food a lot. You may be hungry even though you’ve just eaten. Your appetite may start skyrocketing out of control. You may even do other weird stuff that doesn’t seem apparently related to being hungry, like becoming fixated on things, being crabby or spaced out, or hoarding.
Because hormones are so intimately involved with the brain, the anti-starvation response will have effects on your behaviour and psychological-emotional state. Eventually, if the anti-starvation response is allowed to persist for long enough, there’s a good chance you’ll go medieval all over a buffet.
Because at least one of the hormones, leptin, is related to levels of bodyfat, people’s experiences vary. Fatter people can drop calories relatively lower for longer than leaner people. But still, calories can’t go too low for too long before that bag of Doritos is in mortal danger.