I find this whole thread quite interesting, both the weight loss stuff and the getting jacked on over-caffeinated sugary drink company pre-burn stuff.
There are multiple factors to lots of diet and training modifications, so hard to prove causality; but I've made some changes recently that together seem to have had a big impact. Effectively I was climbing around 7a-7b steadily up til 2013. I logged a 7a+ in Sept 2013 and I'd climbed House Burning Down (7b+) 2011 and El Chocco (7c felt to be 7b by the strong) 2012. Most routes above 7b took me multiple sessions and the 7b+ and '7c' took maybe 4 or 5 sessions. I climbed two font 6Cs (one took two sessions) in Font April 2015, but really I've had climbing on a back burner for the last two years. I had no ascents above 7a for two years and then struggled up Devonshire Cream at 7a in November 2015, after returning to a bit more regular indoor climbing from around October.
Anyway, in January this year I gave up cereal, pasta, white rice, bread, milk, almost all alcohol and refined sugar, other than very occasionally. I've noticed a massive improvement in my mood and energy levels and motivation. I've also lost 10 kg (182cm, 82kg to ~71-73kg). In Feb I went to Font and climbed my first 7A, and then climbed seven more in the week. Weekend after getting back I climbed a 7a+ and 7b in a session, and then next day 7c in a session (5 goes). I used to smash a lucozade or over-caffeinated sugary drink company before an ascent like that, but I've cut that with the other nutritional changes. I did have some pepsi max however, and I do love black coffee.
None of this is particularly impressive stuff, but the before/after contrast is fairly notable. I might be an n of one, but to be honest the changes I've made haven't been difficult at all, and could be worth a bash for anyone looking to improve. I cook loads of interesting food, eat a lot of fruit and veg. I have spiralized courgette instead of pasta which is very filling IMO, but I still eat potatoes and sweet potatoes. I don't believe that cutting carbs totally is healthy, sustainable or necessary. I also eat whatever food I'm served if visiting family and friends. No need to be a dick, and sustainability requires the occasional break. I will have the occasional glass red wine or something with family. I don't drink excessively if I do.
Its certainly clear that cutting the lucozade/over-caffeinated sugary drink company hasn't affected my ability to climb routes that are hard for me. A lot of my improvement might be due to getting back on regular training, but it doesn't account for it all, because I've hit PBs pretty quickly. Losing 10kg is probably a big help, and I think general health/perceived energy improvements have helped. Cutting the booze is a massive one both in terms of training time reclaimed from hangover world, and the negative effects of alcohol on everything.