What is my ideal weight?
In a previous post (why-ride-across-continent-part-2), I said that I would consider my lesson about weight as learned when I reach my target weight and stay within 10 lbs of it. In order to do this, I need to know what my target should be. There are several ways to determine ideal weight. The most common one that health professionals use is called body mass index (BMI).
I am 5 foot 5 inches tall and weigh 238 pounds. This gives me a body mass index (BMI) of 39.8. Based on the body mass index tables from the Center for Disease Control (CDC), I am solidly in the “Obese” category.
According to this table, I should have a BMI of 18.5-24.9. This means I should weigh somewhere between 114 and 144 pounds. I need to lose at least 94 pounds (approximately the weight of a middle school student) to achieve this.
Another way of determining a healthy weight is to look at percent body fat. After all, it is the excess fatty tissue that leads to the health problems of obesity. One way of measuring this is to use a Tanita body composition analyzer, which our school's athletic trainer happens to have. This device looks like a bathroom scale, but it also runs an electrical current through the body to measure body fat. The technique is called bioimpedance, and it works on the idea that muscle, bone, and fat conduct electricity differently. By this technique, I am at 23% body fat. Below is a table showing percent body fat and different fitness categories.
By this measure, I am in the average category, not obese.
For optimum health, both measures suggest I should lose weight, but how much? If I lost only fat, and maintained all of my muscle, I would be at 7% body fat if I weighed 197 pounds. That is the low end of fat for “athletic”. The Tanita analysis says that my Fat Free Mass is 184 pounds. In other words, at 184 pounds I would have zero body fat (an unhealthy condition). To get my BMI to the “healthy” range, I would have to be 40 pounds lighter than 0% body fat.
Those of you who are not science geeks may want to skip to the next section. The graph below illustrates the problem with BMI to assess health. There is a significant correlation between BMI and % body fat, but there is also a lot of variability. My data point would fall in the bottom right corner of this graph, suggesting that BMI is not a good predictor of % body fat for me.
The image below shows the problem in a somewhat easier to understand way.
Both of these men have the same BMI. Obviously, the guy on the left is healthy, but his BMI would put him in the obese range. I am somewhere in between. For those of you who are interested in maintaining a healthy body, I would caution you against using BMI, especially if you are the type of person who prefers to exercise more rather than eat less.
The real problem with BMI is that it creates unrealistic goals. Not too long ago, I weighed under 200 lbs. I believed that I should weigh 144, and tried to lose more weight. I found it impossible to do. I got discouraged, and even depressed about it. The consequence of this was to put weight back on. Had I set a goal based on % body fat, I might have found that 190 pounds was exactly the right weight. I would not have been discouraged and been able to maintain the weight.
Based on all of this, I'm replacing a weight goal with a % body fat goal. Weight is easier to measure though, so I'm going to base my weight goal on % body fat. My plan is this: during the ride, ensure enough protein uptake to build muscle. Eat low glycemic index carbohydrates and limited amounts of fat. Keep calorie intake slightly lower than calorie output. Shoot for 197 pounds (lose no more than 41 lbs). When I return from the ride, I will have my % body fat measured again and reassess my weight goal based on the results.