By Krista Scott-Dixon, PhD

Humans are a clever lot, but they are very bad at a few things. One of those things is precise measurement. This includes things like making straight lines (as every inexperienced carpenter or tailor discovers), guessing how much time it will take to complete tasks (hint: usually it's three times longer than you imagine), and accounting for food intake and energy expenditure (i.e., activity and exercise). In general, people aren't any good at estimating how much they're eating, and how often (and intensely) they're moving around. They tend to overestimate their level of activity and underestimate their food intake. This makes for a difficult time dieting and losing weight.

Not surprisingly, we're not losing weight

Nobody's body breaks the laws of thermodynamics-energy in versus energy out. It just seems like it sometimes. Whenever I have a client who says "I can't figure out why I'm not losing fat! I eat right and exercise!" I know that about 99.9% of the time they're not moving enough and they're eating too much. When we sit down and carefully track their eating and exercise, we discover all kinds of hidden gems: a daily moccacino with whipped cream, a handful of M&Ms (if the hand in question belonged to the Jolly Green Giant), a few days off from the gym here and there, etc. They are taking in too many calories for their individual needs, and they're not expending enough.

Difficulties in measuring how much energy we expend

How do we measure how much energy we're expending? Well, obviously, "guesstimating" is not very helpful. Other methods are not very accurate either. We can get some information from single measurements such as:

• Hours spent
• Bodyweight (heavier people need more energy to carry their bodies around)
• Intensity or speed of exercise
• Steps taken (e.g., with a pedometer)
• Wattage (such as output on an exercise machine)

But single measurements are at best an educated guess. A 22-year old 250-lb. NFL linebacker with 13% body fat is going to have different caloric needs and outputs than a 55-year-old 250-lb couch surfer whose most strenuous activity is getting up from the couch.

The most accurate measurement of the energy we use

The most accurate method for tracking people's intake and output is the specially-designed room, known as a metabolic chamber, used in laboratory-based research studies. Basically, scientists lock volunteers in there, control their food, and measure how much energy they give off in the form of heat, or through observing gas exchange (seeing how much oxygen people take in, and how much carbon dioxide and nitrogen they put out). Only under these very strict conditions can we know precisely how many calories people are taking in and burning. So, unless you're willing to live in a metabolic chamber, you're pretty much out of luck, right?

The need for the Bodybugg to measure the energy you use

Enter the Bodybugg, produced by Apex Fitness. The Bodybugg tries to help people get an accurate sense of how many calories they are expending. It is a small device that is worn on the body, and it uses multiple methods to figure out caloric expenditure.

1. Accelerometer: The BB tracks physical movement and calculates expenditure based on this and gravity.
2. Heat flux: The BB measures heat output-in general, the more heat you put out, the more calories you're expending. (This does not mean that just feeling hot burns calories; this means that your body is generating heat through higher rates of activity, so you can put down the habanero peppers and forget about the sauna for fat loss). This technology was patented in the U.S. in 1996.
3. Galvanic skin response: Unfortunately for all the people who have stuck a fork in a toaster, the body conducts electricity. The GSR monitor measures the conductivity of the skin, which can be affected by physical exertion.
4. Skin temperature: The BB keeps track of skin temperature, measuring changes and correlating these with exertion.

Pros and cons of the Bodybugg

The main advantage of the BB is that it can easily be used and worn by the average person. It is not much bigger than an iPod. People who struggle with their DVD player may find the controls challenging to master, so I recommend finding a seven-year-old child to handle this part. The device also provides immediate feedback - you will know what's going on right away, rather than having to wait until you can input it into a spreadsheet, for example. Although, the BB does allow you to upload your stats to your PC.

The main disadvantage is that it is somewhat expensive. The Bodybugg with armband and digital display is $480. This includes online food logging with custom meal plans, a 3-month subscription to the web-based program, and 2 phone sessions with a Bodybugg coach.

Does the Bodybugg work to help you achieve your fitness goals?

The BB site contains plenty of testimonials, which are standard fare for any infomercial. The rest of the site is rich in visuals, but scant in scientific details. A review of the available peer-reviewed research on the subject did not turn up much, although the BB was recognized as the "Best of What's New" by Popular Science magazine in 2005.

It may be too soon to tell whether this device really does help people meet their fitness goals. However, other research indicates that people given regular feedback and measurement tools tend to report that these tools help them pay more attention to what they're doing. This is especially true if they share the use of these tools with others, such as through online forums or training partnerships. So, the secret to fat loss might just be good ol' interpersonal relationships and paying attention to what goes in your mouth. Still, measurement nerds may enjoy seeing their numbers. And it sure beats having Richard Simmons tell you what to do.