More than a decade ago, I was beside myself with frustration in my nutrition counseling career. I couldn't get to the bottom of a mystery-the mystery of Why a significant number of my clients were always so tired. I was determined to help my clients feel better, so I offered them all types of cutting-edge nutrition advice that I believed would help their energy. No matter what I tried, though, many of my clients continued to experience fatigue. This perplexed me. Becoming increasingly frustrated, I searched high and low for answers.

Fatigue is a national epidemic. Eighty percent of Americans report feeling tired most of the time. Fatigue also is a major public health problem, when you consider how it impacts our lives. When we're tired, we find ourselves less productive at work and less able to accomplish what we want to accomplish. We bow out of things we love to do with the ones we love simply because we're too exhausted. We also become irritable and depressed and unpleasant to be around. As energy doctor Michael Rosenbaum, M.D., is fond of saying, "No one is dying of fatigue, but everyone is suffering from it."

I really wanted to help my clients so that they could enjoy more fulfilled and productive lives, so I approached the fatigue problem as any health practitioner would: I looked first to all the accepted causes. Fatigue can develop because of a wide variety of factors-both medical and nutritional in nature. These include medical conditions such as hypothyroidism (low thyroid function), anemia, and depression, as well as lifestyle factors such as inadequate sleep and lack of proper nutrition. I found that some of the clients who consulted me did indeed have one or more of these underlying medical conditions, but even when such problems were medically or nutritionally treated, most of my clients still didn't find themselves regaining their vim and vigor. Disappointed and baffled, I kept asking myself why.

In numerous other cases, there was no apparent reason that my clients should be fatigued. In assessing these clients, I ruled out common medical causes and looked further to diet and lifestyle. (I usually can quickly identify unhealthy eating and lifestyle habits that undermine energy levels, because I've been a nutritionist for more than 20 years.) But I didn't see any of the obvious mistakes that many people make. The men and women who came to see me were intelligent and health-conscious; they were doing virtually everything right-eating nutritious, light meals frequently, taking broad-spectrum nutrient supplements, and trying to get enough sleep and rest. Some were meditating or practicing stress reduction on a daily basis. Yet in spite of all their efforts, they inexplicably felt sapped of energy. I wasn't quite sure what to tell them. I offered them a wide variety of up-to-date nutrition advice that I thought would help their energy level, but none of my suggestions worked. This confounded me, testing my ability as a nutritionist, so I kept searching for solutions.

After much investigation and analysis, I eventually discovered that the answer to my clients' fatigue didn't involve any of the wellaccepted causes: it was a case of simple nutritional imbalance. If I'd known where to look during those early years of frustrated searching, the nutritional imbalance that was behind so much of my clients' fatigue would have been relatively easy to detect and correct. (You'll learn how you can do that for yourself later in this book.) But I didn't look in the right places, at least not initially. Like many practitioners, I based my advice on my nutrition education, my medical knowledge and interpretation of standard medical tests, and my ability to stay on top of the results of the latest scientific research. These skills didn't help me uncover the answer, however. To crack the code of the missing link to fatigue, I had to follow my gut instincts, use an unconventional diagnostic tool, and analyze the clinical picture that presented itself among the clients in my practice. The following case studies will show you how that picture unfolded in three clients--a picture that spurred me on to find a common, unsuspected, and easily treatable cause of fatigue.

Jennifer, a 31-year-old advertising copywriter, told me when she came into my office that she was exhausted-and she looked it. "I think there's some reason why I'm so tired, but I've seen five different doctors and been tested for everything from anemia to the Epstein-Barr virus. All of the tests have showed up negative," she said, her voice cracking. "Some of the doctors I've seen have insinuated that I might be a hypochondriac. I don't think I am, but I'm starting to wonder."

I could see the desperation in her face and hear it in her voice as she talked slowly and methodically. I asked her to tell me more about her fatigue and the other symptoms she was experiencing. "Well, I have a hard time getting out of bed in the morning, " she said ' "and I need several cups of coffee to feel even somewhat alive. It seems as if my body is always cold and my skin is dry, no matter how much moisturizer I put on it. I've also been steadily gaining weight over the last several years, and I'm frequently constipated. I'm also often depressed, but I think my depression stems from feeling so tired and lousy."

After hearing Jennifer's story, I deduced that one of her problems might be low thyroid function, which is a common cause of fatigue. She told me she'd had standard thyroid profile tests run many times, and they'd all come out normal.