If your new regime still involves alcohol then this could be a factor.
If I drink during a weekend then I can undo any weight loss that week, however no alcohol means a good weight loss that week. Shame I like alcohol
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Start weight: 18 st 4. Current weight: 15 st 10. Fastest run speed: 6.5 mph. Longest run: 13.5 miles. Current goal: To reach 15st 7lb
There is a good article by Powerbar looking at BMR and Caloric Expenditure. If you can work these two figures out and you keep track on how many calories you are consuming each day then weight gain comes down to either
1) Input vs Output in terms of calories (Calories Consumed vs Calories Expended)