Who doesn’t crave for a tuna sandwich with some mayo for example or for a nicoise salad with some mayo dressing?!
But a lot of us are afraid of the word “mayonnaise” as it is known as a fattening and a non healthy kind of food 
Can a low-fat Mayonnaise be a good substitution?!?
First let’s look at the original mayonnaise:
What is Mayonnaise?
Mayonnaise, also known as mayo, is not made with milk! It is an emulsion of vegetable oil and egg yolk and can be flavored with vinegar, mustard or lemon juice and salt. its comes from animal sources and is very high in fat and calories. It raises blood cholesterol!
Mainly we have 2 different types of Mayo?
1- Regular mayo: About 100 calories and 11 grams of fat per tablespoon. Commercial mayonnaise is typically 70-80% fat.
2- Light or reduced calorie mayo: About 40 to 50 calories and 4 – 5 grams of fat per tablespoon.
What is mayonnaise reduced in fat?
“Low fat” mayonnaise contains starches, cellulose gel, or other ingredients to imitate the texture of real mayonnaise. It is usually made using only egg whites and no egg yolks, with the oil used being the soybean oil (natural plant source). If seasoned with salt, pepper, mustard, lemon juice, vinegar and a little paprika, for example, the taste is similar to the traditionally mayonnaise
Mayo is a fatty condiment that should be eaten occasionally! The light version can be a good substitution for people with high blood cholesterol, but intake should also be occasionally!
Both have less than 1 g of protein, between 1 and 3.5 g of carbs and about 1 g of sugar.
Ketchup and mustard can surely be the best substitutes 
http://www.eatlikemira.com/2011/09/12/ketchup-mustard-or-mayonnaise/