"LOSING 60 cholesterol points in a month is a great result but certainly not unheard of," says Laurent Bannock, the British nutritionist whose personalized diet I've been following for the past month. We're in his Santa Fe, New Mexico, office, looking at two blood tests, one from a month ago and one from three days ago. My total cholesterol has plunged from 211 to 151; I've gone from 12.7 to 11.4 percent body fat (I'm five-eleven and 155 pounds); and a urine test shows an almost 50 percent drop in free radicals, the molecules linked to everything from arthritis to cancer.

I've also been enjoying more consistent energy levels and better sleep than at any time in my adult life. If checking my meals against an exhaustive and seemingly arbitrary list of foods—buffalo, spelt, and spinach are in; chicken, wheat, and tomatoes are out—can do all this, I'm a convert.

Bannock, 39, whose clients have included Sting and Princess Di, created my plan after running me through a series of tests that included genetic biotyping, blood and urine analyses, and metabolic screening. He asked me to collect saliva samples during a typical day to track hormonal patterns and had me fill out a lengthy questionnaire. With that data, Bannock crafted a list of foods that targeted my cholesterol, food sensitivities, caloric requirements, vitamin and mineral needs, and glycemic-index targets. In other words, a diet just for me.

"Very few people in the world would have this exact same list," says Bannock, who laid out his philosophy in his 2006 book The Clinical Nutrition Desk Reference. "Food is a pharmaceutical cocktail. You can find benefits in almost anything, but you have to look at the whole picture. Different [ethnic] groups evolved with certain foods and without others. There's just no diet that works for everyone."

The biggest surprise was how much of what I thought was good was bad—for me. All the soy products I love had to go, along with rice and eggplant. Eating like the Japanese, says Bannock, is best only if you're Japanese. He also suggested $150 a month worth of vitamins and supplements to address specific issues during the first 90 days, including cholesterol, detoxification, and stress. Each day started with several powders blended with frozen berries and distilled water, plus a handful of multivitamins, minerals, and omega-3 pills.

I spent the rest of my time trying to get down the ten servings of fruits and vegetables, four servings of protein, seven servings of oils, and assorted other ways that Bannock wanted me to get in 2,600 to 2,800 calories a day. His recommendation that I gain five pounds of lean body mass proved to be the hardest part. I was so worried about not eating the wrong things that if I didn't have access to approved foods, I wouldn't eat enough. By the time I learned to shop for my new way of eating, I'd lost five pounds—though I gained half of that back by the end of the month.

When my experiment was up, I celebrated with a breakfast burrito—eggs, potatoes, cheese, and peppers in a flour tortilla: all on my no-no list—and within an hour felt more sluggish than I had since I started the diet. I won't follow this plan to the letter—Bannock actually encourages a bit of cheating—but my approach to food is forever changed.

DIY: Initial consultations and tests run about $500. Bannock can work via phone or e-mail. laurentbannock.com