If you are at drastically different starting points I am not sure there is a good measurment that is fair to both of you. If you use percentage lost (like the Biggest Loser show) and you are 250 with a goal of 150 and your friend is 200 with a goal of 150 then if you both hit your goal you will have lost 40% of your starting weight (100/250= .40) but your friend will have only lost 25% of their starting weight (50/200= .25). You will have the same problem using BMI as a percentage change. The heavier person always has the advantage because they start with a higher number. You could use your ending BMI (whoever is the lowest BMI at the end of a time period) but this would favor the competitor that starts lighter because their BMI is already lower. The lighter competitor could not lose any weight and still have a lower BMI after the higher weight competitor lost a significant amount. (Assuming they are both the same height the heavier competitor in my example above could lose 50 pounds and their BMI would then be the same as the lighter competitor's starting BMI.)
If you based the competition as total weight lost in a period the heavier friend has some advantage because generally, weight is easier to lose at the beginning of a transformation and it becomes harder as you come closer to your healthy weight.
Perhaps the competition could be based on hitting your caloric deficit targets. There may need to be a penalty for too large a deficit to ensure the competitive nature doesn't lead to unhealthily low calorie eating. On the plus side this would reward healthy behaviors on the minus side the competitor with the best transformation may not be the ultimate winner.
They all have their good and bad points. Hope I have given you some thoughts. Good Luck!!
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Ron
Male, Age 53 Height 5'-11"
Start, Spring 2009....,.. 270.0 lbs
January 21, 2010. ....,...255.0 lbs (Joined Fitday)
September 10, 2010..,..223.8 lbs. (-46.2lbs)
Mini-Goal......................225 Achieved 9/21/2012
Mini-Goal......................220 Achieved 10/26/2012
Current......................... 216.2 lbs. (-53.8 lbs)
Mini-Goal....................... 215
Goal.............................. 200
My log: http://www.fitday.com/fitness/Public...Owner=rpmcduff
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