Hi Cvaldez1991.
Congratulations on your weight loss.
I'm not actually an expert, but I too found a lost a lot quickly at first. In me, I think it was mainly fluid I was retaining. Fast initial loss seems to be common from what I've heard.
Something I was told to watch out for is that muscle weighs more than fat, so as you increase your lean body mass (and decrease your body fat percentage) weight loss may slow (as you put on more muscle or tone up) and you may even gain weight.
But then you would have increased your lean body mass and hence your metabolic rate would have also increased. This is good because then you will burn more calories even while at rest.
In the long term, this should make weight loss easier to continue and once you reach your target weight it should be easier to maintain.
Maintaining a calorie deficit (difference between calories eaten, calories burnt from activity, and metabolic rate) each week will slowly decrease your weight, but try to resist the temptation to fast track. Deficits are usually about 500kcal to 1000kcal per day from what I've found on-line.
Much higher and you could burn muscle or send your body into starvation mode from what I've found on-line. That's bad because burning muscle makes your metabolic rate decrease and makes maintaining or losing weight more difficult - hence you are more likely to put it back on afterwards. Going into starvation mode causes the body to lock onto resources in an attempt to preserve itself, this also slows down weight loss.
I entered your stats in an on-line BMR calculator - height 5' 9", weight 316 lbs, age guessed 20, assuming female otherwise its different then your BMR is about 2259.9 kcal per day. (used bmi-calculator/bmr calculator).
Then comes the activity modifier. I use 1.2 for me (thats sedentary, 1.4 is low active, 1.6 is somewhat active, 1.7 is active, and 1.9 is very active). So I use my BMR x 1.2 as a guide - with modifications due to a 5 week cycle I seem to have.
The trick now is to determine how much you actually burn in total cause you want to avoid starvation mode. So you'd pick the appropriate modifier, multiply for BMR by that number and thats about your metabolic rate. Add in the calories burnt from exercise and you have your calorie expenditure (approximately). Then try to maintain your nutritional requirements within range of what you are using. IE try to consume about 500kcal less than you burn for example. 1lb = 3500 kcal approximately, so 500kcal per day is about 1 lbs per week.
Eat too little = starvation mode, Eat too much = weight gain.
Exercise too much = injury, exercise too little = low metabolic rate and hard to lose weight
Luckly theres a healthy range
I've done the eat too much, exercise too much, and exercise too little.
Been there, done that. Ouch.
I spreadsheet my consumption of food and activities, and get the spreadsheet to back calculate to estimate what my actual activity modifier was for the week prior and then use this as a guide.
And remember as your weight decreases your BMR will decrease as it is a function of weight including fat and muscle. Muscle consumes more calories than fat, but fat does take some although not much. Its possible your BMR x activity modifier will decrease but as activity goes up the modifier increases quite a bit. 1.9 is nearly 60% more than 1.2.
Its going to be a slow journey though, a common target from what I've read is 1 to 2 lbs per week after that initial loss. At a target of about 139lbs for a BMI of 21, thats about 2 to 4 years.
A slow journey, but the health benefits are worth the effort.
Engineer.
EDIT: I am a slow typer, BugDudes answered while I've been plodding along. Hes right though, these things average over time and our bodies adjust. Good luck.
EDIT: Walking for 3 miles, possible about an hour depending on your speed would be about 500kcal, a formula I found online was 0.53*weight in pounds*distance in miles = calories burnt. Good walking shoes are helpful, I learned the hard way. Watch out for chaffing, learned that the hard way too. Google them for solutions, depends on the amount of walking though.
. I had 50/50 odds though. 