To remain healthy and keep the weight off, you must watch what you eat.

Obesity is associated with an increased risk of several chronic diseases, but being thin or losing weight does not resolve that risk if you fail to maintain the change in your diet.  You will need to keep a healthy diet to keep your risk low.  Even if you do not gain the weight back, eating poorly will create an increased risk of type 2 diabetes, heart disease, increased risk of some cancers, and others.  

The biggest trap most dieters fall into is that they can return to their old lifestyle after losing weight.  Weight loss is not a temporary change.  Instead, the change needs to be a permanent change for better health.  If you focus on a lifelong change, you will be more likely to end in successful weight loss maintenance.  A mere 300 extra calories per day will result in 1-pound of weight gain every 12 days or 30 pounds in a year.  

Bottom Line: Obesity is linked to several chronic diseases, such as type 2 diabetes but an unhealthy diet is also a risk.  Many people with obesity are metabolically healthy, and many thin people are not.  Once you lose weight, healthy eating is required to keep the weight off and maintain a lower risk of disease.  Just because you are thin now, does not mean that you can eat whatever you want.  Focus on the future and long-term health through a healthy diet and exercise.