WHEN I received the results of a routine cholesterol test this summer, I was certain there had been some kind of mistake. I’m young, unstressed and healthy, or so I imagined. I work out, too, and most impartial observers - and some partial ones - would describe me as lean. Plus, I eat a nutritious diet, I swear. So why did my LDL levels surpass my I.Q. - or, for that matter, Einstein’s?

The facts were stark: My genes predisposed me to metabolic syndrome, my doctor told me. Like my forebears, I was on a fast path to heart disease and diabetes. My doctor ordered me to reduce my carbs and come up with a more stringent exercise plan. I’ve rarely monitored what I eat and how much exercise I get. I had no idea how to go about the logistics of it. How would I count my carbs? How would I track my fitness routine?

Of course, there are apps for that. I set out to scour the market for devices and programs to help me and any family member who wished to join me in my low-carb adventure improve our health. I found two kinds of technologies: fitness trackers to monitor physical activity, and P.C. and smartphone apps to track diet. I spent weeks testing several of them. And while I found a few to be quite helpful, they were all just short of fantastic.

I tried four high-end fitness gadgets: Nike’s FuelBand ($149), the Fitbit One ($99.95), Jawbone’s Up ($129.99) and the BodyMedia FIT wireless armband ($149). I also threw in a plain-Jane pedometer, the Omron HJ-720ITC, which I found for $31 at many stores online.

All of these devices work in a similar way. You attach them to your person (the FuelBand and Up fit around your wrist, the FIT goes around your upper arm, and the Fitbit and Omron pedometer can be placed in a pocket or clipped to your belt). Then, as you move, the devices measure your activity.

Unfortunately each device had major drawbacks. Even though I had gotten the proper size, I found that the Up and the FuelBand did not fit well around my wrist. They tapped against my desk while I typed, and they slid about uncomfortably when I washed the dishes. (They are both water-resistant.) BodyMedia’s FIT, meanwhile, is about the size of a man’s large wristwatch. Positioned directly against the skin around the upper arm, it is ungainly — I found it distracting when I was in a short-sleeve workout shirt, and strange-looking under a nice button-down shirt.

The pedometer and the Fitbit were easier to handle; I hardly noticed them crammed with my keys and phone in my pocket. On the other hand, because they are not wearable, I often forgot them on my bedside table, where they did no good.

Still, among these vast offerings, I found the Fitbit and the cheap Omron to be best. The Fitbit is an unobtrusive slab of plastic about the size of a U.S.B. thumb drive. Its software — which is available for Macs and Windows P.C.’s, as well as iOS and Android devices — is simple to learn and offers plenty of graphs and stats to track your progress. The most useful is a graph of your activity over the course of the day: you can see how many calories you burned while at work and alter your behavior accordingly. Maybe go for a brief walk after lunch?

(I was a big fan of Jawbone’s Up software, too, but I ultimately found it too limited: It works only on Apple’s iOS devices; the company has not yet made versions for P.C.’s or Android devices.)

The best thing about the Fitbit is its wireless syncing capability. It comes with a tiny receiver that plugs into your computer’s U.S.B. port; whenever your Fitbit is near your machine, it sends its data over the air, no physical docking required. It also syncs directly to your phone over Bluetooth. (You do have to plug your Fitbit in to charge it, but only rarely — you can go more than a week between charges.)

The Omron, by comparison, does not do wireless syncing, and its optional P.C. software is pretty basic. But paucity is its beauty. No setup is required. Just turn it on and leave it in your pocket. At the end of the day, peek at its screen — in large, readable type, it shows a single stat: how many steps you have walked that day. The Omron does not promise the world, but it delivers enough information to keep you healthy.

While all of these devices made it easy to track my activity, they were of little help in monitoring my diet. The Up, Fitbit and BodyMedia FIT include food-logging options in their companion software, but I found them all to be a little slow. The problem with tracking food is that you eat a lot of it, so you need something that will make quick work of adding the many items you have consumed throughout the day. Ideally, the software would let you add multiple items with a single action, would remember what you eat repeatedly and would be connected to a vast library of foodstuffs — so that when you told it that you ate, say, a slice of meatloaf from a Cook’s Illustrated recipe, it could instantly calculate your plate’s nutritional information.

I tried a few programs that promised to be so savvy, including FitDay and Lose It! But there was one that ranked far above the rest: My Fitness Pal, a free calorie-counting app that runs on the Web as well as iOS devices, Androids, the BlackBerry and Windows Phone. My Fitness Pal did exactly what I describe above: It let me add many foods at a time, and remembered my most frequent consumables so that I could add them with a single tap every day. I also loved My Fitness Pal’s bar code scanner. Point your smartphone’s camera at the U.P.C. symbol of that peanut butter you are slathering on that piece of bread and the app instantly understands what you are eating.

But My Fitness Pal’s killer feature is its enormous database. The app claims to have knowledge of more than a million food items, from apple strudel to zucchini walnut bread. In my tests, I found it almost creepily comprehensive. It had caloric info on that Cook’s Illustrated meatloaf, as well as a flounder recipe I made from Bon Appétit, and pretty much anything you could ever buy in a grocery and even many restaurants. If it does not have an item, My Fitness Pal allows you to enter your own recipe; for example, you can type in the ingredients of your mom’s apple pie, and it will figure out how many inches a slice will add to your waist.

Combine all these features and you get an app that makes dieting less of a drag. With My Fitness Pal, I am able to log an entire day’s meals in just a minute or two. I do yearn for the time when some kind of sensor will automatically track my intake. But that day is not imminent. For now, tracking your diet with My Fitness Pal is the next best thing to eating any old thing you want.

###

By FARHAD MANJOO