How does a weight gain affect a marriage?

The answer is same as to how does a lack of career for one partner affects a marriage

When partner in marriage doesn’t feel good about themselves, they tend to think negative about their body, their existence, their career, their identity.

They think negatively about themselves first and this tanks down their self esteem. Once self esteem, self image and self talk is hampered, the partner finds extremely difficult to love the other partner because his or her own heart is full of regrets, pain and resentment.

How can a muddy water jug pour out clean water. How can a cluttered mind and unhappy heart ever have a happy environment?

Its extremely important to work on ourselves if we find ourselves in that situation of low self esteem and negative self talk.If partner is going through this, then it becomes all the way important for other partner to give as much love as possible which the partner understands and motivate them to see specialist and experts which can help them come out of negative self image.