What makes a marriage happy? In addition to health and prosperity, the weights of the husband and wife might be a critical component of marital bliss, according to a recent scientific study. But — perhaps surprisingly — it's not how heavy or thin the wife is, but how her weight compares to that of her spouse. What you need to know:

What exactly did researchers discover?
Experts from the University of Tennessee looked at the body mass indexes (BMI) of 169 couples, and also asked them privately about their varying degrees of satisfaction in their marriage over time. Married men were happier when their wives had a lower BMI than they themselves had. While that might not be too surprising — generally speaking, men tend to like thin women — the researchers also found that wives were happier when they were smaller than their husbands. In other words, "thinner wives make both spouses happier," says Benjamin Radford at Discovery. It's not clear exactly why this relative weight difference makes couples happier.

Can heavier women be happily married, too?
Of course. The size of the wife isn't the real issue. What's more important to marital happiness is the wife's weight compared to her husband's, not in comparison to the rest of the world. The study reveals that "women of any size can be happy as long as they are with the right partner," says researcher Andrea Meltzer, as quoted in the San Francisco Chronicle.

Do these findings apply to all married couples?
No. The researchers limited their investigation to recently married couples under the age of 35, so the findings might not apply to older couples or those who have been married longer. "The effects of relative weight could definitely change over time," says Meltzer, as quoted by ABC News. For couples who have been together for decades, it's possible that "attractiveness plays less of a role, [and] perhaps relative weight has less of an effect on satisfaction."

Sources: ABCNews.com, Discovery, San Francisco Chronicle