great question! I think a lot of people have saboteur problems, and talking out the underlying reason for it with the saboteur is a great idea. Other thoughts:

If he's simply in the habit of showing love/thinking about you with a food gift, ask him to switch to inexpensive flowers or magazine instead. That way, he still gets to be thoughtful and kind.

Give him another alternative to be caring. Say, "instead of buying me food, I'd like it ever so much more if you read this book," and hand him your LC book.

Accept the gift, say, "Thanks--I don't want it right this second," then later, when he's doing something else, run it down the garbage disposal. Worst case scenario is him catching you at it? Then at least he knows how serious you are about not eating junk.
If those don't work, I'd switch tactics...maybe don't say anything--no refusal, no thank you, no explanation. Perhaps he's trying to (for some unconscious reason) get a rise out of you, and if you don't give it to him, he may abandon that tactic.

HTH, and best of luck to you!