A friend of mine in London, ON tried that diet, but gave up due to the cost.
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A couple weeks ago John Tory was on CFRB's morning show speaking to Ted about losing weight on the Berstein Diet. He actually said that he only consumed 800 calories per day along with exercising in the mornings.
I would call that a starvation diet myself and very harmful.
What is he thinking???
My mom and I tried it over the summer (about a month and a half). We didn't go to the clinics, just got ahold of the food lists and took a few supplements to replace some of the stuff that you need when you go on such a strict diet...you don't get the same "motivation" as going to the clinics but its extremely expensive (and my mom is involved in the healthcare industry and consulted with a doctor who runs one of the clinics so we were both pretty aware of what to do/watch out for).
Anyhow, we both found it to be amazingly effective (and neither of us is very overweight, just wanted to lose maybe 10lbs). For the first three days (when you are getting rid of all your glycogen stores by eating pretty much no carbs) you can feel a bit crappy (headaches, little energy), but once you're into ketosis (you check your urine to see if you're excreting ketones) and all your glycogen stores are gone (so then you're burning fat whenever calories out>calories in) I personally felt great. I didn't even want to eat carbs/junk food...I was quite happy with the allowed foods/quantities (you can eat alot of protein so you're not really hungry...some feel "deprived" without the carbs though). I had lots of energy (wanted to exercise more than usual). We both saw alot of weight loss and muscle gain. I still stay away from carbs (and I don't miss them) and I've stayed at a stable weight. I think the diet really made me think much more about portion sizes and the true nutritional value of what I'm eating (and I eat much healthier now for it---even at the university caf!)
Its all about eating filling foods that are low in calories (carbs suck in this respect) and exercising.
All that said, I think this diet is meant more for extremely overweight people...they are already at great risk for health problems and the risks of a "starvation" (I don't know if I would call it this...I was probably eating 1000-1200 calories) are thus not as worrisome.