You sound like me when i decided this time last year to improve my fitness. I was also 170 pounds and on my 5'6 frame it wasnt i suppose hugely overweight, but the weight wasnt my main problem. I just wanted to get back the fitness level i'd let slip. Oh yes, I'm 21 lol.
I didnt/dont follow any specific plan. I just downsized my portions, changed my eating habits to mostly low-fat and started counting calories. I came down to about 1200 a day and started up with just walking at first. Then as my fitness improved moved to jogging and running and joined the gym where i started weight training for strength and toning. I've lost quite steadily at a rate of about 2kgs or about 4.5 pounds a month and I reached my goal in may this year (which was actually 135 pounds) My body kept losing however and has since leveled off at the current 125 which i've been maintaining.
My "diet" included fruits and veges for the majority, I cut out a lot of bread and nearly all pasta and rice (but still had the odd bit...no sense completely depriving myself) and had protein in the form of meat about 4 times a week. I have a LOT of dairy, mostly low-fat yoghurts and skim milk, i added things like beans and nuts, and generally just expanded out my field of variety. I suddenly discovered how GOOD a lot of veges and things actually tasted. I've never taken supplements or used meal replacements or protein shakes or any of that stuff.
I guess the bottom line is it did take awhile, and that weight loss of 2kgs a month is averaged out, some months it was less, others more, the first couple (as you've discovered) I didnt lose much at all BUT, my clothes fit looser
So just be patient, do some reading, find out what you think will suit your lifestyle/needs best and adapt it to yourself.
Livi (feel free to say hello if you want
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