I'm not a specialist. If you want to do serious weight loss, find a dietitian.
Exercise on a weight reduction diet is hard, but doable. It requires calibration.
Couple of facts
Following is NOT true: If you burn N calories during exercise you can eat as much afterwards.
First of all --- human body just works like that: big energy expenditures seem to kicks start adaptations that conserve energy [*].
Don't eat sweets before workout. Here is why: sweets increase blood glucose levels, which induces pancreas to eject insulin into bloodstream. Insulin reduces glucose levels, if this reduction overlaps with reduction of glucose levels due to exercise your glucose level might be too low (which is not fun).
Also in extreme cases you might faint.
Losing weight with training alone is hard. Seriously.
Bar of chocolate is 600kcal, an hour of intensive workout (for me).
Always have some chocolate/protein bar during workout. Realising that you are hungry and 20km from home is not fun.
If you want your muscle mass to grow [†] eat some easily digestible proteins after workout. Which means some protein supplements --- there are not much easily digestible, low calorie, protein sources in the wild.
If you aim for burning fat workout should last 30-60 minutes. Muscle have an energy reserve for about 15 minutes, so you actually start to burn fat after thus 15 minute period.
It's better to have lower intensity workout for one hour than very intensive 15min one.
Regular exercise is good, it should increase metabolic rate somewhat.
How do I exercise now
Hour before excercise I eat bigger lunch. Extra 200kcal --- usually wholemeal pasta cooked al dente.
Wholemeal pasta has lower glycemic index than normal pasta, also pasta cooked al dente has lower glycemic index than normal pasta. [‡] .
During the workout I always have some protein bar.
Usually single workout lasts about an hour and burns 600kcal.
After the workout I eat some extra protein (supplement)
Usually I workout twice or thrice a week.
Source, (web archive).
Dugas calls this phenomenon "part of a survival mechanism": The body could
be conserving energy to try to hang on to stored fat for future energy needs.
Again, researchers don't yet know why this happens or how long the effects persist in people.
"We know with confidence that some metabolic adaptions occur under some circumstances,"
said David Allison, "and we know with confidence some behavioral compensations occur under
some circumstances. We don't know how much compensation occurs, under which circumstances,
and for whom."
|[†]||Muscle mass is not a goal in itself. When doing weight reduction it is good since it increases base metabolic rate --- keeping a kg of muscle tissue uses a lot more energy than 1 kg of fat tissue.|
|[‡]||Glycemic index is (roughly) how fast glucose levels rise after eating certain product (and how fast it falls afterwards). Before workout you want to eat things that release energy slowly so glucose levels don't crash during the workout.|