Training to failure or not training to failure has been and may still be a debatable subject matter, and may be dependent upon the person and/or persons.
Diet can definately affect weight training performance and results, there is no question on this. Likewise, the type of stimulous (weight training) coupled with rest and recuperation time (and ability, sleep, hydration, etc) can also effect results and performance---that can be indifferent or separate from the diet.
While I claim to be no expert, I would assume that if your not getting the results you want, I would look at the--totality---of your weight training and diet. Along with evaluation whether your getting enough days of rest and recuperation time (where the REAL GROWTH OCCURS).
One MUST provide enough REST, we can atribute some basic amounts, but some may need more then the traditional amount (I need at least 5 sometimes 6 days between body part, with the exception of BI's, they seem to need a bit less time), and others just train once a week with results.
The circumference or totality of ALL CAN effect results (not JUST the weight traing type, though it could be the weight training type by itself)
I think most would agree (in its basic form), that sometimes even IF everything is close to being right, one day you go to the gym and your on top of the world, and progress reps on your lifts and/or add weight for progession. At other times, there is none (which may or may not be an indication something is in fact wrong), and sometimes after this bout with no progression, you go back in and progress nicely. However, with this being said, I do believe one ought to go in the gym with the frame of mind there gonna progress, and yes, even the mind can effect whether you progress or not (like: "damn, I dont want to do this today" or "I wish I wasnt here", etc)
I wont argue the no failure or to failure issue. There are alot of material on this subject. For the most part working to "momentary" failure on healthy individuals seems to work for a large variety, while trying the other works for some.
Personally, if I get a snag in the gym, I dont look at my routine first. I see how much water im drinking, timings of my food (and what it was, what were my calories like, etc, etc), how many days rest did I provide this muscle (and was it enough--too much?,etc), how much sleep, is it possible work interfered (meaning stress, anxiety, etc), how did I feel in the gym (energetic, sluggish--what?), etc. I look at these type of things, and of course the routine: how long have I been doing this? Have I given it enough time?, did my MIND interfere, etc, etc, etc.
Im NOT saying that NOT training to failure is NOT for you. I am just saying look over everything, its not "necessarily" your routine or whether your training to failure or not to failure that may be the problem,
This was not meant to confuse, but rather just state it could be something else.
You didnt say how long you were training and what your routine is like. Maybe if you get more specific, you can have some other knowledgeable eyes look at it, and provide a keen insight into the problem, it may not be the "to failure" or "not to failure" issue. Some just starting out get great progress at first (body is just flat not used to this stimulous, and tends to respond fairly well most of the time), if you have been at it for while, it tends to slow down (of COURSE, I think this is logical), but this IS NOT saying regular progression doesnt occur if person sets a progressive program
Let me give you an example of how diet CAN effect your routine: Im in deficit diet, and have been for quite sometime (MONTHS; now im in a zig-zag experiment with myself). Through these months, I have progressed (albeit, slower compared to a surplus), and this has definately effected the AMOUNT of weight I use on a body part-----and has caused plateaus. My body weight is low, body fat is low, my calories are low,,,,,,,UH,,,,,,I think we can assume the weights on my lifts are going to be effected...no? So at times I played diet experimentation when a plateau surfaces. Sometimes I will surround my routine with the BULK of my diet before a major body part, and this sometimes breaks it. Sometimes, I will add +5lbs to the first set, and go back down to the previous wgt., and then next leave the first as is, and add +5lbs. (this lowers my rep AIM, but I at this time, have a different goal and mind set).
I know without a doubt, that if I maintained a continued surplus (say 7 days), my weight progression would sky rocket after being in a deficit diet for so long (and isnt saying, I dont or havent overfed once in a while, as I think one should reasonably), my body weight would go up, and I would (all things equal here) possibly grow accordingly (at least strength, since I'm an old man).
Let us not forget the uses of other LIFTS to assist other LIFTS in progression. Take the bench press, how many muscles at work here? If you say pecs (oh boy, yes of course), but its not the only one, we have for example, the Delts, Triceps, the back to a minimal degree, etc). So wouldnt certain types of Military Presses, tri work (ie, close grip bench, and other tricep work), maybe even
bent over row (or other back work type, to save argument), assist in the bench progression? Yes, it can.......can I say. Food for thought. Sometimes adding or taking a exercise out can assist in problems (on the stimulous side of the equation), changing rep range that you use, there are so many things one can do, other than the arguement of whether to go or not to go to Momentary failure.