The response below is intended for educational purposes only. It is not intended to be legal advice. Nothing in the response constitutes or creates any attorney-client relationship.

In general employment in Texas is at-will. This means both the employer and the employee can terminate the employment with or without cause at any time. An exception to that rule is when the employer and employee sign an employment agreement which details under what circumstances either party can end the employment relationship. Your question states you never signed a contract stating you would not work if you gained weight. The real question is whether you signed any document with your employer limiting its right to terminate you for any cause. Absent that, the employer may be within its rights to act as it did.

Another exception to the general rule is job discrimination based on different treatment because you a member of a protected class. However, weight is not a protected class under State or Federal labor laws.