Research by the American Diabetic Association found that dieters who were not successful after numerous weight-loss efforts were drastically underestimating their calorie intake and overestimating their energy expenditures. Studies show that dieters who write down everything they eat consume less than those who don’t monitor their meals.
Now while us UnDieters don’t need to worry about calories, this research brings up an important point; we often see what we want to see. So a food diary can reveal errors such as not waiting long enough between a Protein and a Starch meal, improper food combinations, too much sugar, eating too much too late at night, etc.