Hopefully the staff at your doctor's office will be sympathetic to your sensitivity about your weight (you’re certainly not the only one). You can ask them not to weigh you, but you may get some resistance from the nurse who checks you in, as this is part of the routine.
That's because your weight, or more accurately your BMI (body mass index, which is your weight taking account of your height, calculated by dividing your weight in kilograms by your height in meters) and weight changes are an important “clinical sign.” Like your blood pressure and pulse rate, it gives insights into your health.
Ideally, your BMI should be between 18.5 and 25. Above 25 is overweight, above 30 is obese. Being significantly underweight is far less common, but it can also be a health risk.
For those who are sensitive about being overweight, yes, it's a risk factor, but it's only one of many. Blood pressure, blood sugar, cholesterol level, family history, how much you exercise, and what you eat are all crucial factors in your health.
Where the fat is distributed on your body is also significant to your risk; pear-shaped is healthier than apple-shaped (fat on your abdomen instead of your butt and hips). So it's recommended that a woman’s waist should never be above 35 or a man’s above 40 inches.
As confirmation that weight is not so much of a risk factor on its own, a study showed the risk of death is not increased in “overweight” people with a BMI of 25 to 29.9. It's possible to be perfectly healthy if you exercise and eat right. In such cases, sensitivity about being “overweight” is just a reflection of what weight our culture tells us to be.
Changes in your weight can be a sign that something is wrong. If it’s going up, you may have some illness like an underactive thyroid or heart failure making you retain fluid. Losing weight when you aren't trying is probably a more sinister sign. It can indicate some hidden illness like cancer.
If you're not letting the doctor keep track of your weight, make sure you are keeping a record of any changes. Monitor your weight and tell your doctor if you are gaining or losing. Report how much weight you've lost or gained and how quickly.
Providing you understand the significance of your weight, and monitor it yourself, it’s not unreasonable to refuse to be weighed when you go in for an office visit.