Perhaps. But people who give up on relationships also let themselves go as well. On the other hand, when you're a couple, you might be tempted to let yourself

Perhaps. But people who give up on relationships also let themselves go as well. On the other hand, when you're a couple, you might be tempted to let yourself go, but at least there's a chance your mate will refuse to go. Since our behavior is driven by environment (a la we observe the norm, and conform) you'll resist temptation and stay healthy. Habits are easier to maintain when you're not alone. This alone might give couples the edge.