|yeah you're looking for the VLOOKUP function. Search in help and you should be able to see how it works, but I would imagine you have a table with each food on sheet 1. Column A=Food name, B=carbs, C=protein, D=fat and E=calories|
Then on your real sheet it would be
A2 is your quantity, so the VLOOKUP gets multiplied by this.
The B2 references the item name.
Sheet1!$A:$E refers to your table on sheet1.
The "2," tells the vlookup to pick out column 2 (carbs in this case): this would be changed to 3 for protein, etc.
Finally, "FALSE" means get an exact match.
Hope this helps