Not equal at all, in other words.

According to an American study from Ohio State University the woman gains weight after marriage, whereas the man gains weight after a divorce. The team looked at weight gain in the two years following a marriage or divorce among more than 10,000 people in the United States surveyed from 1986 to 2008.
"Clearly, the effect of marital transitions on weight changes differs by gender," lead author Dmitry Tumin, a doctoral student in sociology at Ohio State University, said in a university news release. Tumin continued by adding “Divorces for men and, to some extent, marriages for women promote weight gains that may be large enough to pose a health risk.”

In Sweden, the couple shares the weight.

“Both men and women tend to gain weight in a relationship,” says Stephan Rössner, Professor in Health Related Behavioral Science at Karolinska Institutet. According to Rössner, all great events in a person’s life affects his or her weight, and the most common way is to continue on the path you’re already on. That is, if you already have a tendency to be overweight, you’ll gain weight if something important happens in your life, while the opposite is true for a thinner person: If you’re already on the thin side, you’ll loose weight.

Source: Marriage and Divorce Trigger Weight Gain (Ohio State University study by Dmitry Tumin, lead author and doctoral student and Zhenchao Qian, professor and chair, Department of Sociology)