Ok, some low carb options:

The Food Emporium between Abbey Street and Liffey Street has lots of Help-yourself buffets where you can load up your plate with chicken drumsticks and pork for 8.95 euro.

The Port House in South William Street (a few doors down from Butler's Chocolate) and its sister Pintxos in Eustace Street both serve lots of tapas sized portions of meat, cheese, fish and nuts.

The Corner Grillhouse on South Great Georges Street has good steak,

Tante Zoe has lots of low-carb options, includiing a cream cheese starter that's a meal in itself, and some good fish and steak.

China House Restaurant in Moore Street is very Chinese and serves stuff like fried intestine, but also things like lamb soup, lamb cubes, chicken bones, pork hocks, and lots of fishy things, all dirt cheap by Dublin standards.

Bar Italia has great Atkins-friendly antipasto, and the best coffee in Dublin.

The Market Bar has lots of good options.

101 Talbot (in Talbot Street) has some good options and is very helpful about replacing carbs with green veg.

Fallon and Byrne in Wicklow Street stock Lindt 99%. So does the Avoca food hall in Suffolk Street.

McDonalds in Grafton Street and O'Connell Street both have McCafes where you can get a cafe Vienna which is made with huge amounts of real whipped cream, no sugar added.