--- NEW ANSWER APRIL 15 2013---
I have been using Scivation XTEND™, but due to it containing Ace-K wanted to look into replacing, and investigating if I could rather use natural sources. Casey's answer mentions Ned Kock's site and using eggs, so I did some investigation. Here is the comment I left Ned today...
I revisited this post since I am interested in replacing supplements with real foods.
Had a quick look at egg whites versus Scivation XTEND™ powder for (L-Leucine, L-Valine, L-Isoleucine).
Scivation XTEND™ (1 x 12.5g serving):
3.50 g L-Leucine
1.75 g L-Valine
1.75 g L-Isoleucine
Egg Whites [raw] (2 x 33g large eggs):
0.70 g Leucine
0.50 g Valine
0.40 g Isoleucine
Recommendations per day [80kg]:
3.6 g Leucine (≥ 45 mg/kg/day)
1.8 g Valine (≥ 22.5 mg/kg/day)
1.8 g Isoleucine (≥ 22.5 mg/kg/day)
Because BCAAs have been shown to aid in recovery processes from exercise such as stimulating protein synthesis, aiding in glycogen resynthesis, as well as delaying the onset of fatigue and helping maintain mental function in aerobic-based exercise, we suggest consuming BCAAs (in addition to carbohydrates) before, during, and following an exercise bout. It has been suggested that the RDA for leucine alone should be 45 mg/kg/day for sedentary individuals, and even higher for active individuals. However, while more research is indicated, because BCAAs occur in nature (i.e. animal protein) in a 2:1:1 ratio (leucine: isoleucine: valine), one may consider ingesting ≥ 45 mg/kg/day of leucine along with approximately ≥ 22.5 mg/kg/day of both isoleucine and valine in a 24 hour time frame in order to optimize overall training adaptations. This will ensure the 2:1:1 ratio that appears often in animal protein. It should not be overlooked that complete proteins in whole foods, as well as most quality protein powders, contain approximately 25% BCAAs. Any deficiency in BCAA intake from whole foods can easily be remedied by consuming whey protein during the time frame encompassing the exercise session; however, an attempt should be made to obtain all recommended BCAAs from whole food protein sources. International Society of Sports Nutrition position stand: protein and exercise. http://bit.ly/116NQCS.
So it seems that according to the above recommendations two large egg whites are unfortunately not going to achieve those levels, and are pretty poor in comparison to the 'best of breed' BCAA powder.
--- ORIGINAL ANSWER FEB 7 2012---
I use myprotein.com (UK): bcaa and bought 500g of the powder for £20.39.
I fast from dinner to lunch the next day (21:00 - 14:00), taking 10g for breakfast to fill this fasted gap. I then take 10g pre-workout at around 19:00, and eat my biggest meal afterwards. I am still playing with this all. With my schedule I don't think I need more than 20g of BCAA a day.
I would say though that if I was working out in the morning I would take 10g pre-workout and 10g post-workout as I would be continuing my fast until 14:00.
In my mind the purpose of the BCAA is to prevent muscle loss during the fasted state, and thus depends on the level of activity. Since I am sitting at a desk from 08:00 to 14:00 I just take 10g when I wake up. I then take 10g just before leaving the office post-workout which I feel really helps with my workout. Dinner follows which is my largest meal of the day.
NOTE: I used to buy tablets which were more expensive but if you can swallow 10 tablets, potentially worth the extra cost. This is the first time I have purchased BCAA powder and it tastes like hell and is not water soluble. I took the plunge and now take both BCAA and creatine via a tablespoon of powder piled onto the back of the tongue and then chugged down with water. Honestly if you are doing powders this is quickest and most bearable method. Five seconds of blerrrghhhh versus trying to drink a pint of unmixed watery bile with floating goblets of powder. Nooo Noooo Noooo!