First thing I would love to tell you is that Slim Fast doesn't work.
My personal experience with Slim Fast: Tastes like garbage, gained 10 pounds in a month, and hated doing anything that involved cardio.
My personal experience with Primal Lifestyle: Love what I eat, lost 5% body fat in 2 months, and love doing moderate to low impact cardio.
If you weigh in at 235 pounds, I would suggest avoid eating 900 to 1,000 calories a day. Simple math you would be doing more harm to your body than good. Focus on body fat rather than the scale, best advice I was ever given!
235 pounds I am assuming your lean body mass would be around 160.
So eat .5g to 1g of protein per pound of lbm = 80 to 160grams of protein.
Keep carbohydrates down to around 20-50grams.
Fat should be .8 to 1.5g of body weight = 188g to 300g.
So now then lets see how many calories we are eating...
2250 of fat, 320 of protein to 640 of protein, 80 to 200 of carbohydrates.
That gives you a total of 2,900 calories.
But wait where is the science that says you should eat 2,900 calories?
Calorie Needs :
Calorie Calculator, Calorie Intake, Calories Required For Travelers, Calories For Visitors.
So although I was off by 157 on average that shouldn't make much of a difference it should put you in a daily calorie deficit.
Now from my personal experience I don't believe in calories, I believe in carbohydrates.
I eat around 5/6k calories a day since going Primal I have lost 5% body fat in only 2 months.
I wouldn't say this method works for everyone but it works for me.