I've been doing some more serious research on this myself, and I think it breaks down to a really simple solution.
During most of the day, for the first 20-30 minutes of aerobic exercise, you are burning stored glycerin. Then you start burning fat. However, if you work out first thing in the morning on an empty stomach, you go into fat burning almost immediately. According to one source I read, this means that you will burn fat 300% more than you would in the middle of the day or the evening. So you get more fat burning out of a 30 minute workout in the morning than you would out of a 45 minute workout at the same level on your lunch break.
Additionally, some light strength training can do wonders. Add some muscle to help burn fat...1 kilo of muscle will burn 50 - 100 calories a day as opposed to the 5-7 that a kilo of fat burns. So add in 2 or 3 strength workouts a week to crank it up.
In any case, 100 lbs. in a year is beyond impressive. He very well may have hit a point where his body is adjusting itself. I'd guess that in any case, some sort of change is in order to get things moving again. Is his additional 50 lbs. realistic or would he be in better shape at 170?
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Tom
"It hurts so good..."