From Diet Blog Share: I am 35, and I have been overweight my entire adult life, and within the last few years I crossed into the obese category. I’ve tried to get into shape many times in my life and have always failed, until now. Approaching heart disease age, I finally decided it’s time to start taking my health seriously, and 2 months ago I began eating healthy, counting calories, and exercising every day. For the first time in my life I’ve gotten past that initial hump, where exercising stops being a dreadful, painful chore and starts to feel good. I never thought I’d actually look forward to exercising every day, but I do, I’m starting to crave it. The problem is I can’t concentrate. I am a computer programmer, so not being able to focus on my work makes me pretty worthless. I will sit down at my computer in the morning, open a project, and just sit there dreading doing anything. I’ll take “quick” breaks to go browse sports or news websites that end up lasting hours, and before I know it it’s lunch time and I’ve accomplished little.

The afternoon goes by similarly, and I’ll usually end up working late after dinner trying to make up some time. By Friday I may have ~20 hours of work logged, and I try to commit to making it up over the weekend, only to be thwarted by similar focus problems. This started almost immediately after I changed my diet and began exercising. It’s not a lack of motivation or laziness, I spend the time at my desk trying to work, I just can’t seem to focus on tasks that require concentration. There’s no doubt I’ve thrown some pretty drastic changes at my body, and I’m sure that screwed up my chemistry somehow. I started taking a multi-vitamin (1-a-day) about a week ago thinking that would help, but so far it hasn’t. I’m not depressed or tired, in fact I’ve never felt better, and for the first time I’m enthusiastic about my health. But, not being able to work is quite an expensive trade-off to be healthy. Is this a common side effect of exercise? Any suggestions?

The rest is here: 
[Forum] I’ve Lost My Focus Since Starting Exercise