Does this dramatically get you in shape, I know 7 days is not long but under these conditions did you see a noticeable difference? I am very interested in doing something like this some day.
As in physically? Well you'll lose some weight off course as you burn so much more calories under the effort of walking. I think I was around 215 going up and in pretty decent shape. Didn't weight myself for a day or two after coming down but when I got back to England I was just over 200 and had a few big meals inside me already. But it could also be the fact that we've spent the preceding few days in Tanzania eating very little.
Thing about acclimatisation is that you either have it in you, or don't. At the top or near the top I saw overweight people laughing and joking around, posing for pics, while also seeing slim, lean and seemingly in shape people suffer greatly and not make it at all all the way to the top. For me it was very hard. I'm not going to claim I have the greatest build in the world but I have clearly more muscle mass than the average person so it takes more oxygen to keep me going. On summit morning I swore I was near death. Imagine the most tired you've ever been, compound that x10 and put an elephant on your chest after all that. Afterwards I was thinking that I may have been in actual shock. But the team of porters that go with you can see when you start to struggle and walk with you, forcing you to drink as much water as you can. Some of our porters have summited over 500 times. 500 fucking times! It's incredible to do it once, never mind twice.
My tip would be to take an extra day. Do the 7 day trip. Believe me, you're going to appreciate that extra day. Especially if you're a big guy.