While it's not as common as people may think (or hope), thyroid conditions can certainly be a factor in weight gain. Your thyroid controls your metabolism, so when it's working slower than normal (hypothyroidism), it will inevitably lead to weight gain.
"Unexplained weight gain is one symptom of this condition," Dr. Apovian says. "Other symptoms of hypothyroidism include fatigue, constipation, feeling physically weak, sensitivity to the cold, and puffiness of the face." If you're noticing these symptoms, visit your doctor for a simple blood test to be sure.
Your family is overweight
As much as you can keep your weight in control with lifestyle choices like diet and exercise, you still could be predisposed to obesity, thanks to the wonders of your genetic makeup. If your mom started to rapidly gain weight around age 25, for example, and you notice the same thing happening to you, Dr. Grunvald says you may be SOL. Thanks, mom!