Yo-yo diet may increase your risk of heart disease and premature death.  

A number is just a number, but if your weight yo-yos up and down, losing weight may be bad for your health.  I am not talking about the daily fluctuations that occur in all of us.  Some weight fluctuations are normal.  Personally, my weight has varied in a day by up to 2-3 pounds.  It is virtually impossible to gain 3 pounds of body weight in a day, but you can gain water weight which may appear on a scale as 3-5 pounds or more in a couple of days.   

Obesity is tied to many chronic medical conditions that are deleterious to your health.  Too much weight increases your risk for diabetes type 2, high blood pressure, heart disease, degenerative arthritis, and more.  Almost all experts will agree that weight loss is good for your health if you are overweight or obese, but can weight loss be bad for your health.    

A new study looked at weight fluctuation and coronary artery disease.  The study looked at body weight changes for over 9500 subjects.  The researchers found that a variation of fewer than 2-kilograms in overweight or obese subjects resulted in a significant increase in heart disease by 4%.  There was no associated risk for those of healthy weight who had a 2-kilogram variation of their weight.

The bottom line: Yo-yo diets or fluctuation in weight is terrible for your health, but some weight fluctuation is normal.  If the scale shows a five or more pounds difference in 1-2 days,  the weight change is likely due to water weight.  I would guess that being obese is worse for your health, but further studies are needed to confirm this.  I recommend that you lose weight and stay at a healthy weight.  If you cannot attain a healthy weight and trying to do so will create a yo-yo effect, it might be more beneficial not to lose weight, but more research is needed.