Ego depletion is a very well known theory. It says that willpower is limited, and the more you use the less self control you'll have. If you are stuck eating radishes while smelling freshly baked chocolate chip cookies, you might get frustrated and give up on your next task easier (as one of the most frequently cited studies on the topic showed). If you diet on too low of calories, you'll eventually binge. Makes sense right? Turns out it seems it's not so simple.
Another study came out a couple days ago questioning the theory. This controversy became big earlier this year, when a study came out with more than 2000 subjects, showing no effect. If you search pubmed for "ego depletion" you'll find a ton of studies on it, accepting it as a real thing. However more recently it's been changing. This study showed the same around the same time. There are a lot of reasons the original findings are being brought into question, and it's not being replicated, a problem which has plagued other findings also. Study after study after study make it hard to believe how this theory was so unquestioningly accepted for so long.
However, there's not been a lot of research on why. This series of studies finds that it could just be that we think it is limited. The subjects who didn't think it was limited didn't lose self control after a task meant to cause them to, based on the theory. So apparently these scientists used shitty studies to convince us willpower is a resource we can deplete, and in doing so caused us to actually lose willpower due to thinking we would. That's just fucking awesome. Thanks for that, science.
But now that I got the obligatory science shit out of the way, what does this mean for us?
It means we need to stop accepting the theory. Certainly doing something that's too hard on us for too long CAN cause negative effects. But we need to stop thinking that it WILL, because it might not. Willpower has been tied in with motivation, and anecdotally we've likely all had a time when we were able to do something difficult for far longer than we thought. We can't use that as an excuse and let it hold us back. How we think can affect our outcomes more than we think sometimes, as I'll be touching on in my obesity stigma article that's coming soon.
You probably can stay adherent to your diet, or go to the gym and get through your workout. You just have to know it.