What unique individual factors can make it more likely that I'll gain weight?

Obesity is a complex disease that is the result of many different parts of a person’s life that happen over a long period of time. Things that can affect your weight include:

Genes and family background. – Obesity tends to run in families. But there is not one “fat” gene. There are many genes that may work together to make you more likely to gain weight. The situation you live in also affects your genes. When you are a baby or young child, your parents or caregivers control your eating and physical activity. This family background can influence your weight as an adult.
Metabolism.  – People’s metabolism rates (how fast your body “burns” calories) may vary for many reasons, and this can affect weight gain and loss. For instance, men usually have more muscle and less fat than women do, so men’s bodies might burn more calories more quickly. A woman’s metabolism may change throughout her life, such as with the hormonal changes that happen during puberty, pregnancy, and menopause.
Age.  – Your metabolism may slow down as you get older. Also, as we age, we lose muscle. With less muscle to burn calories, we need fewer calories.
Trauma. – Many events in the past that you didn’t have control over and are not your fault can affect when and how quickly you gain weight. Women who experience serious, negative events during childhood, such as abuse or a parent with a problem with alcohol or drugs, are more likely to have obesity as adults. Researchers have found that girls who are sexually abused may be more likely to gain weight faster as young adults and develop obesity at a younger age.  Also, women who experience a traumatic event at any time and develop post-traumatic stress disorder (PTSD) may be more likely to gain weight quickly after the traumatic event and develop obesity.
Medicines.  – Many of the medicines that women take every day, including medicines for mental health conditions, sleep, and high blood pressure, can cause weight gain or make it difficult to lose weight. If you take any prescription medicine and have extra weight, talk to the doctor or nurse who prescribed the medicine about the best ways to safely lose weight and possible alternatives to that prescription medicine.
Sleep.  – Not getting enough high-quality sleep can lead to weight gain. Researchers think this may be because low-quality sleep can affect your hormone levels, which can affect your appetite and food choices. Not getting enough sleep to feel rested may also affect how much physical activity or exercise you get throughout the day.