Is it reasonable to want to lose 20 lbs. in 3 months? I want to lose 40 lbs in 1 year or less.
Usual disclaimers: Not a licensed nutrition expert :D
Conventional wisdom is no more than 2 pounds per week. You're talking about 1.5 lbs/wk so in the safe but difficult range. It gets harder as you approach your target weight, but 40 pounds in 52 weeks seems possible.
Remember that to maintain that new lower weight you're going to need a permanent adjustment in diet so be sure if setting up an aggressive plan for loss that it is sustainable. Consider that if you started eating now the diet necessary to maintain your ultimate goal, you would lose weight (albeit gradually) and eventually taper in to your desired weight.
Just my $0.02 w/o jumping into the religious wars and what constitutes a good diet ;D
I agree 100% with what GalacticHero said, and I'd also add that as you start a new exercise program, you'll need to keep in mind that if this is new for your body, you're going to be building muscle along with losing fat. So you may see that you're getting slimmer and more toned (along with all of the other great benefits like better cardiovascular heath, mobility, flexibility, and balance), but your scale may not change as much as you'd like at times. From personal experience, I'd say it would be a good idea to take measurements as well as weigh yourself. You might experience a quick weight loss in the first month and then see yourself toning more than losing for a while.
As far as losing 40lbs in a year, I think it's absolutely possible. Yesterday I had my one-year "anniversary" of starting my weight loss journey, and I've lost 86lbs. You can definitely reach your goal with determination!
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