Definitely less. My husband and I are empty nesters and even when our son comes home for the weekend our food bill is less. If we're eating out I always have leftovers for at least the next two days. My leftover salmon dinner turned into two days of lunch. It's easier to prep breakfasts for the week. I usually make a frittata or mini omelets in my muffin pan. Quick, easy and high in protein. I have more than enough for breakfast for the week and even have them for dinner sometimes. As someone else posted the vitamins and protein drinks probably make it all a wash.

Food costs more. I really adhere to the perimeter of the grocery store (i.e. fresh meats and veg).

Cooking it takes longer too as I adhere to a low GI/low carb diet.

The food will still spoil so I freeze a lot

I definitely spend less going out, and go out less frequently, but now I have to buy supplements and I buy higher quality whole food ingredients, so the amount of money spent on food/nutrition is pretty equal. I definitely save a crapton when I go out to the movies, no more $16 MegaMeal bucket-o-popcorn and giant soda ;)

It may depend on your current spending/eating habit right now. I used to buy real food and cook before, same now.  My food budget for one person could go down, but since now they are 2 people in the house- and I do need better quality food... (no more pasta night, or just salads day), the overall quality of food is much higher...so we spend more on food for 2 people, than we did before. 

Adding supplements, plus docs visits, lab work, etc etc.... I spend more money than before to just be me. 

We do eat out sometimes, and I do eat less, but...again , I have to be very careful what I eat- so that may cost more than just going to buffet or fast food place. 

I spend more at the grocery store now because I'm buying better quality foods and produce plus the cost of food is rising.  I prepare most meals except for the once weekly dinner out.  If you account for protein powders, protein shakes, supplements, and spices, it's probably still costs less than when we were eating out 3-4 nights a week or picking up a pizza on the way home. 

Plus I like trying different recipes.  I do a lot of prep and crock pot cooking on the weekends which saves money.   I've found several good soup recipes which can be made using dry beans and other inexpensive ingredients that last for multiple meals.  About every other week, I'll get a rotisserie chicken ($5) which is also good for 4-5 meals  depending on what I make. 

At 18 months out, I do a lot of salads with a protein source for lunch and protein with veggies for dinner.  I rarely use coupons since most of what I buy is fresh or frozen. 

Quality food and vitamins are priceless.  My costs went up for the reasons you describe.  However, Groomy is THIS CLOSE to getting off his diabetes meds.  His diet/diabetes is so much better now that he is away from prepared foods!

Considering the economic and physical costs associated with 30+ years of diabetes (which he would experience if he lives into his 70s), I will pay through the nose for good quality food and not think twice about it.  I will give up expensive hair cuts and professional hair coloring to make up the difference. It is THAT worth it!!!

Higher quality, more protein sources (chicken, fish, etc.) versus less cheap fillers (pasta, rice, bread, potatoes) but yes less real estate so smaller portions. Though ala carte or buying smaller isn't always cheaper. 

High quality supplements are not cheap and specially in the beginning you may be using some of those.

I don't eat fast food or crap out of vending machines anymore. Dinners out were $$$ pre-op (apps, meal, drinks, dessert) now it's meal and I take 1/2 home :)

I cook a lot... which usually means a savings as leftovers can be utilized and turned into lots of other meals.

I figure... my being off 8 medications, lack of Dr. & specialist co-pays makes it all worth any money spent.