Such option was not presented in the hypothetical scenario. It'd be trivial anyway to make the tasteless goop tasty with some flavorings.
Most things that innately taste good -- stuff that you could drop in a blender and drink and it'd still be agreeable -- are fatty, salty, starchy, sugary, or some mix of all these. Healthy and good-tasting food requires pleasant textures and careful composition that allows a small amount of fat, salt, starch, etc. to enhance the flavor of the whole meal.
"Fatty" is not a synonym for unhealthy by the way. A lot of people consider high fat/low carb diets to be healthier than the reverse.
The problem is, McDonalds meals are not healthy, full stop:
Mcdonald's - Big Mac Meal With Fries and Coke With No Onions
http://www.myfitnesspal.com/food/calories/mcdonalds-big-mac-...
1130 Calories, and 67 grams of sugar. Call me when McDonalds modifies their meals to consist primarily of protein/fat calories.
The burger itself is fine. You wouldn't go to Subway for a nice sandwich and drink a liter of Coke afterwards and a bag of chips and complain about how unhealthy it is.
Here you can get some nice fresh crispy raw carrots instead of fries.
Right...that's why I called the scenario a false dichotomy.