Hey.. I bought some "Slim Fast Optima" shakes on the weekend. They state on the box "keeps you full for 4 hours". I thought.. yah.. sure.. whatever. Well you know. I am on my pre-op, and up until 8:00 pm tonight, I had only had 3 shakes, and several bottles of water all day. I honestly felt full all day. I can't eat late at night, and I was out running around at 8, so I went through McDonald's drive thru (as I had only had 190 x 3 calories all day) and I had 1/2 of a grilled chicken wrap. So.. for anybody that's fighting hunger, and can drink shakes, I highly recommend these ones. They're great!