Some fall for beautiful eyes while others are smitten with a smile.
But when it comes to deciding on true love, you might be better off looking at your intended's waistline, according to a study published in the American Journal of Clinical Nutrition.
Scientists have shown that we tend to marry partners with a similar level of body fat to our own.
Flab, or the lack of it, is just as important as background, class or age in determining who we choose to spend our lives with.
It is thought the phenomenon - known as assortative mating - could be a key factor in the obesity epidemic.
Children of overweight couples are likely to inherit genes that make them prone to putting on weight too, and so be more likely to have a weight problem themselves