Here's the 'Losing an Argument' thought for the day, from a man's point of view:

I actively plan to always lose every argument, to never have the last word. In a perfect world, your spouse would have the same mindset, but it doesn't always work out like that, so it might just be you, for the rest of your life. That's fine. It's not that bad. 

There's a good chance that your wife is a nurturer, or a caretaker, and she might occasionally want to care for you by... let's say by giving you vitamins, or being sure you stayed away from unhealthy foods. If you respond to that by saying that 'I'm a grown man and I'll do what I want', you'll win, and she'll stop.

But you'll close off part of her. She'll stop 'nurturing'. She'll stop caring. My friend, that is a dangerous place to be. 

Better to let her nurture. If you decide not to, don't do it in the moment. Give in and then bring it up later in a non-threatening manner. In my case Penny used to bring me quite a few vitamins in the morning; I picked my moment and asked her if we could reduce that to the ones she thought were essential. She still gets to nurture (a core part of her being) and I... am mostly healthy. 

Because of the likely size difference between you two, she needs to feel that she's on even ground with you in discussions. We can't just force our way. Lose a few arguments. Or most of them. You'll thank me later.