One of my favorite studies, an oft-replicated and cited study, tracks several hundred people who claimed to be "diet resistant". Using a technique invloving "doubly-lableled water" they were able to determine that every single person in the study who claimed to be diet resistant was overreporting their exercise and underreporting their calorie intake:

https://www.nejm.org/doi/full/10.1056/nejm199212313272701

Of course, this was a study of obese people. If you're doing a study on healty-weight people who are trying to build muscle, you may get far fewer people who will lie.