Many people have a weird relationship with their bathroom scale. Some people hide it, others cross check the weight with a 2nd scale (and sometimes a 3rd), some don't ever go on it, and others may go on it but refuse to look at the number. Body weight is inconsequential, body mass composition (amount of body fat and lean muscle mass) is more telling. Muscle weighs almost two times as much as fat. It is possible to be "heavy" and ripped. When Arnold Schwarzenegger was a competitive bodybuilder his body mass index rated him as obese even though his body fat was south of 5%! What if you weighed the same but looked cut and toned, would that bother you? I hope not.
Most dieters have been told to stay off the scale fearing they might get discouraged by the slow loss of weight. This conventional wisdom is flat out wrong. Research has shown that individuals who weigh themselves daily are a lot more successful at losing and keeping weight off. Daily weigh-in's ensure weight doesn't sneak up on you, keeps you focused on your goal and provides opportunities to celebrate weight loss. Moreover, it is much easier to get back on track if you gained a pound or two than six or seven pounds. One major caveat to daily weigh-ins is a concern for the adverse psychological effects on people who might over fixate on the numbers and/or suffer from eating disorders. For these individuals I would not recommend a daily weigh-in.
Our body weights fluctuates a lot throughout the day (mine moves about 4 lbs.). The daily fluctuations are not caused by an increase in body fat. Let me say this again in another way because it is important: A daily weight increase you (may) see on the scale does not come from fat. Here are the reasons for daily weight changes:
Water Level Changes - This is the biggest factor of weight fluctuation, after all you are 70% water. A gallon weighs 8 lbs and drinking liquids can add temporary weight quickly; when you shower your body absorbs small amounts of water; not drinking enough water will force your body to retain fluid.
Food - Some of the food you ate last night and today is likely still in your body resulting in a temporary gain until you fully metabolize it.
Hormones - Menstruation causes water retention (and bloat) which equals weight gain.
Sodium (Salt) - Did you have fast food yesterday? Besides the fact that fast food is horrible for you and will probably give you disease, the copious amounts of salt in it cause the body to retain lots of water.
Exercise and Activity - Strenuous physical activity causes immediate fluid loss due to sweat. If the water is not replaced your body goes into dehydration mode and retains more water.
Sugar/Carbs or Protein Based Diet - Simple carbohydrates like cookies and pasta will cause you to hold water and temporarily raise weight. Similarly, high protein and low carb diets give a false impression of weight loss when the body is simply losing glycogen and water weight.
Defecating and Urinating - Pooping and peeing cause obvious weight loss.
If you know yourself, and I hope you do, and can't handle seeing weight gain, then maybe only weigh yourself once per week. Otherwise, make sure to weigh yourself naked on the same scale at the same time every day. Personally, I like to do it first thing in the morning after I visit my fortress of solitude. This is when I weigh the least.
Sources 1. http://link.springer.com/article/10.1207%2Fs15324796abm3003_5?LI=true : Self-weighing in weight gain prevention and weight loss trials 2. Cooper Z, Fairburn CG: Cognitive-behavioral treatment of obesity. In Wadden TA, Stunkard AJ (eds),Handbook of Obesity Treatment. New York: Guilford, 2002, 465–479. 3. Touyz SW, Lennerts W, Freeman RJ, Beumont PJV: To weigh or not to weigh? Frequency of weighing and rate of weight gain in patients with anorexia nervosa.British Journal of Psychiatry. 1990,157:752–754. 4. http://ajcn.nutrition.org/content/66/2/239.short A descriptive study of individuals successful at long-term maintenance of substantial weight loss