To reach your goals, you may need to eat more

The idea is simple: If you time your meals to coincide with your workouts, you enhance the muscle-building effects of those workouts. (I'll discuss this in more detail in chapters 6 and 7.) But coordinating fitness and food also increases the TEF of those meals. A small study at the University of Nevada Las Vegas found that subjects burned off 73 percent more calories when a meal followed a strength-training session. Six of the nine subjects in the study were women. Another study, from the University of Colorado, found that habitual exercisers have a 25 percent higher TEF than nonexercisers. The subjects in the latter study were all men, but it shouldn't matter; other research from that same group has shown there isn't a gender difference in TEF. All that said, the best way to illustrate the importance of eating enough calories is to take a closer look at what goes wrong when you don't. WHEN HORMONES ATTACK As I was writing this chapter, in December 2006, a study came out showing that underweight women who became pregnant were 72 percent more likely to have a miscarriage. "Underweight" was described as a body mass index (BMI) of 18.5 or less. To give you a reference point, a woman who is five-foot-four and weighs 107 pounds would have a BMI of 18.4, and would thus be considered underweight in this study. Two things jumped out at me as I read that: First, I'd guess that most of the women we see on TV and in the movies fall into the "underweight" category. So the role models you grew up with, and our daughters will grow up with, are at an unhealthy weight, never mind unrealistic for most who 'd try to achieve it. Second, it doesn't surprise me at all to learn that a low body weight-usually achieved with a low-calorie diet-would interrupt reproductive function. A woman's reproductive hormones are highly sensitive to nutrition, for a simple evolutionary reason: It makes no sense to get pregnant during periods in which starvation is a distinct possibility. So your body shifts its priorities elsewhere, fueling your brain and internal organs rather than allocating those precious energy reserves to a hungry offspring. For most of human history, being pregnant and then delivering a child in times of famine gives the family two distinct disadvantages: not only is the family risking the loss of the fetus, but the mother's health would be compromised as well. I bring up reproductive function, and reproductive hormones, because they're a very good stand-in for your general health. If you're premenopausal and your estrogen is low-as it would be if you're not eating enough-you're not going to build the healthy reserves of bone tissue that you'll need when you're postmenopausal and your bones start shrinking from lack of estrogen. And it's not just the reproductive hormones; if you're starving yourself to achieve a photogenic level of emaciation, you're also disrupting chemicals that, ironically, keep your metabolism up and help you control your weight. These disruptions help explain why rapid-weight-Ioss diets are such a metabolic disaster. When you start regaining weight-and you always will, since selfstarvation is impossible to maintain for most of us-a much higher percentage will appear on your body in the form of fat, rather than the normal mix of fat and lean tissue. Let's start with estrogen. In sports medicine, it's well established that female athletes who train hard and don't get enough calories will experience amenorrhea. That is, they'll stop having periods-a clear sign of low estrogen levels. More recently, it's been shown that female athletes with low estrogen levels will have more stress fractures. As they go through life, the loss of bone minerals will continue to haunt them, leading to much more serious fractures in old age. Studies by Anne Loucks, Ph.D., have shown that exercise isn't the sole culprit; it's the lack of calories combined with serious exercise that lowers estrogen levels. Amenorrhea is an obvious symptom of undereating. When you go a couple months without a period, you know something's wrong. But most of the consequences of undereating aren't immediately obvious. Among the hormones that could go haywire: Luteinizing hormone, which is responsible for triggering ovulation. Leptin, which regulates appetite and metabolism (less leptin means more hunger, and less satiety from the food you eat) . Thyroid hormones, which control not only your resting metabolic rate, but also the metabolism of protein, carbohydrates, and fat. One kinda-sorta good way to tell if you have low thyroidhormone levels is if you notice you feel cold after eating. These hormones decline in hibernating mammals, whose body temperature falls rapidly when it's time to sack out for the winter. So if your levels are low, your body might feel as if it's going into hibernation after a meal. Cortisol, a stress hormone, rises when you're chronically undernourished, and it's about the last hormone you want more of. Cortisol strips your muscles of protein and turns it into sugar for energy. That's why cortisol is also linked to higher blood sugar, as well as higher blood pressure and suppression of your immune system. The net result of these hormones getting all medieval on you is what I've harped on throughout this chapter: Your resting metabolic rate slows. You' re voting for a leaner body by working out, but you're voting against it by eating too little food.The Carb Wars Are So Over WE LIVE IN an age in which the phrase "refined carbs" has the same dreaded resonance as "we've found irregularities in your expense report. " Still, you don't have to look far to find women who still believe "fat makes you fat." A corollary belief is that dietary protein is somehow unsavory-you know there must be something wrong with a protein-rich diet if people like the late Dr. Atkins were in favor and all the esteemed experts of nutrition science were opposed. So if carbs are satanic, fat makes you fat, and protein is the province of people you've been told not to trust, that leaves us with a steady diet of ... water. (In case you're wondering, I'm not going to say anything negative about water. It would make for a more entertaining book, but it would also be difficult to do with a straight face.) Let's relax, take a deep breath, and think all this through. First off, it's worth remembering that humans are the original hybrid vehicles. Our bodies can run on anything. I mentioned in Chapter 3 that we prefer to burn a mix of carbohydrate (in the form of glycogen, or blood sugar) and fat throughout the day. But that doesn't mean you actually have to eat a balance of carbs and fat. Your body can make triglycerides, the form of fat it uses for energy, from carbohydrates. Or it can make glycogen from fat. And if you somehow managed to eat pure protein without any carbs or fat, your body could turn that into several different forms of energy as well. My point is that your body is astoundingly adaptable. Because it's designed for survival in many different climates, with many different forms of sustenance, you could eat just about anything that falls into the general category of "food" and live to tell the story to your grandchildren, assuming you don't have to eat that suboptimal diet for long. Here 's an example of how flexible your body is: Your brain is just 2 percent of your total body weight, but sucks up fully 20 percent of your daily calorie expenditure. (Sort of makes you want to use it more productively, doesn't it?) And, despite the fact your brain is made mostly of fat, it runs entirely on sugar. But that doesn't mean you have to eat 20 percent of your calories in the form of carbohydrates. You could eat more, or you could eat less, and your brain would still work. Which brings me to the concept of macronutrient ratios. Don't get put off by the jargon. Yeah, I know, I say that a lot, but this time I really mean it. There are only three macronutrients: carbohydrate, protein, and fat. Everything else is water, ash, or alcohol, the last of which doesn't fall neatly into the other categories. It's technically a carbohydrate but has some fat-like qualities. (If you're ingesting enough alcohol for this to be an issue, I suggest you rethink that strategy.) I have good reason to burden you with the eight syllables of "macronutrient ratio." Since The Zone came out in 1995, we 've had a fascination with the idea that there's an ideal combination of the three macronutrients, a ratio that will work for all people, all the time. Is there such a thing? Let's discuss.