Here is a recent Thin From Within entry from Psychology Today:
It’s a common question, with an answer that has shifted over time: “How often should I weigh myself?” asks the person hoping to lose. That person may well know the excitement of seeing the lower number….as well as the distress that an unchanged—or worse, higher!—number can bring. More than once, this same person may have experienced the “weighing in” as the “giving up” point of an effort to eat differently.
It used to be that people were cautioned against weighing themselves too often. Over-checking could lead to compulsiveness, inaccurate assessments of real losses, discouragement, it was believed. Weighing in less often—say once a week at a set time, or even less often, perhaps only at the doctor’s—seemed better for maintaining perspective and avoiding the impulsive overeating that might follow disappointment. However, that thinking has changed. In fact, Dr. David Allison, of the Nutrition Obesity Research Center, University of Alabama, recently asserted that “none of these fears is justified” when looking at the evidence for frequent weighing.
Opinion began to shift as The National Weight Control Registry consistently noted “frequent weighing” as one of the practices leading to long-term weight loss maintenance. The Registry tracks over 10,000 people who have maintained significant losses over years. It appears that weighing in, even daily, is one habit that helps people stay aware of variations that warn them if they start to drift from good habits. They can then correct themselves quickly and early if necessary.
The “weigh frequently” recommendation, though, leaves many in difficult straits. Ideally, it should come with a clear warning label. For example, anyone with a history of anorexia nervosa, even if partly or fully recovered, should usually avoid a behavior that can indeed become compulsive and reinforce the idea, always, that “less is more”. Active bingers, too, frequently find scale numbers upsetting in a way that can destabilize their efforts to eat more moderately and less addictively.
Frequent weighing requires the ability to react with relative calm if the scale number is up. More specifically, that means the ability to remember that daily fluctuations are normal. That a day or two or more of increased exercise, more careful choosing and portion awareness, can pull the number back on track. That you may not love being a little “up”, but occasionally it happens and doesn’t spell hopelessness or failure or personal shortcoming. All of this may sound reasonable enough, but is far from easily achieved for many who struggle with size and eating.
So, to the “use the scale” advice, that clear warning label might add: “unless it triggers even a small amount of disordered eating behavior.” In other words, the scale should work to “spot” you as you work to eat more healthfully, not dictate whether and how you eat, nor how you feel about yourself as a person in the process of trying to change. If it works for you, use it. If not, then don’t.