The thinner the wife, the happier the marriage, a new study suggests.

Published in the July issue of Social Psychological and Personality Science, the four-year study of 169 newlywed couples found that husbands were more satisfied initially and wives more satisfied over time when the women were thinner.

There's a lot of pressure on women in our society to achieve an often unreachably small weight, said Andrea Meltzer, a doctoral candidate at the University of Tennessee, and a lead author of the study. The great take-home message from our study is that women of any size can be happy in their relationships with the right partner. It's relative weight that matters, not absolute weight. It's not that they have to be small.

And while Meltzer is uncertain of exactly how relative weight affects marital bliss, she has a guess.

One idea is that attractiveness and weight are more important to men. That might be why we see this emerging at the beginning of the marriage for husbands, and their dissatisfaction might be affecting wives' satisfaction over time.

When other marital stressors were eliminated - depression and income level, to name two - the finding held up. But as Meltzer cautioned, relative weight is not the only factor that affects marital satisfaction.

Obviously, a lot of things play into relationship satisfactions and this is just one of them, she said. It's not a guarantee to be happy in a relationship.

According to Susan Heitler, a couple's therapist in Denver and author of PowerOfTwoMarriage.com, men and women tend to be happiest in a relationship when the men are more powerful in a benign way, ABC News quoted Heitler saying.

The good news is there are many dimensions that symbolize power for men, she said, adding height, weight, earning capacity, intelligence, education level and personality are all empowering. Those signs of bigness lead to a subconscious feeling within the woman of more security and, in turn, more marital satisfaction.

The importance of relative weight can, however, change over time and vary between couples. Of the 169 couples in the study, 94 percent of them were white.

Heitler said this is because in American and European cultures, special emphasis is placed on weight, whereas, In Africa, weight is a sign of fertility and voluptuousness. Heavier women are prized in that culture.

Moreover, age may be a small factor, with older people not attaching too much importance to weight; in the study, all of the couple were younger than 35.

The effects of relative weight could definitely change over time, Meltzer said. As attractiveness plays less of a role, perhaps relative weight has less of an effect on satisfaction.