I keep a collection of articles about the health benefits of maintaining a healthy weight (and the health hazards of gaining weight). I find focusing on health, rather than appearance, is motivating for me.
"Abdominal Fat at Middle Age Associated with Greater Risk of Dementia"
"...Overweight & obesity in middle age leads to chronic health problems like cardiovascular disease, diabetes and dementia later in life...."
"Fat in middle age can cut women's lives short..."