I've been on an experimental protein only diet for 11days now (I'm only using protein powders (whey, hydrowhey, casein & a complex blend) and absolutely no food. Depending on the intensity of my workouts my daily micronutrient values are as below;
Protein: 171gr - 255gr
Carbs: 27gr - 31gr
Fat: 16gr - 21gr
Sugar: 8gr - 12gr
(1007kcal - 1407kcal)
Though I'm using BCAA and Glutamine powders and EAA tabs separately. Also using quite a few additional supplements to support my body & systems.
I train pretty heavy, 5hr krav maga, 1hr yoga, 2hr cardio, 2hr 15min PT sessions (mostly compound exercises), 3hr 15min isolation training (and burpees) over 11 separate sessions in 6 days per week. In everything I do, my effort/pain level is 8.5-9.5/10. And as of today I'm adding two 20km running sessions per week.
I'm 28, work full time in a senior managerial position(in reference to your question about low carbs) and so far haven't felt any downsides of this diet and heavy exercise. To be very honest I've never felt so alive and strong in my life before. I'm simply exploding with energy!
You can take a look at my thread at "anabolicminds . com / forum / nutrition-health / 224181-highly-experimental-extreme . html" (sorry couldn't post links due to low post count, just remove all the spaces) for more information. I've an attached file with any details you could ask for. I was complaining about weight loss coming to a stop but has slowly started again now. My fiancee hasn't been able to stop complimenting the progress I've with muscle growth & definition lately as my upper body has changed incredibly over the last 7 days!
It's an extremely controversial plan for anyone to follow and extremely strict but can give you a few ideas to shape your own system.
Cheers!