Hi Bubbleboy, welcome!

As Sinbad says, you need the fat to use as fuel. It's not a high protein diet, as people often erroneously describe it, it's a high fat, adequate protein, low carb plan.

I would add too that it may help if your wife reads your copy of DANDR. I'm a nurse myself, and was also brainwashed for years about fat.
Remind your wife that every study done proving the "evils" of fat (esp saturated fat) has been performed on groups of people who also eat high carbs. There have been no studies ever anywhere showing that a high fat plan (in the absence of sugars and starches) causes any harm.
You might also suggest to your wife that she has a look at "Low Carb Studies" on the orange bar at the top of the screen. She will find some reassuring info there.

Cheers, mate.

Rosebud