No matter how you slice it or scoop it, butter is more fattening and less healthy than light mayonnaise. Per tablespoon, the contrast is stark. However, you probably wouldn't use the same amount of each on a sandwich. Typically, a tablespoon of mayonnaise is used the same way a pat of butter is used. Even with these adjusted serving sizes, light mayo wins. Keep in mind that neither product is good for you, so avoiding both of them is the best way to maintain a healthy diet.
Calories and Cholesterol
Gram for gram, butter is much more energy-dense than light mayonnaise. A tablespoon of light mayo has 36 calories, the same number of calories in a pat of butter, but a full tablespoon of butter has nearly three times the number of calories, with 102. Butter is also considerably higher in cholesterol, with 11 milligrams per pat and 31 milligrams per tablespoon. A tablespoon of light mayo has only 2 milligrams of cholesterol, making it a better choice for your heart health.
Fat and Cholesterol Content
Let's face it: Mayo and butter are both high in fat. Even light mayonnaise has 3.3 grams of fat per tablespoon, compared to 11.5 grams of fat in a tablespoon of butter. That may not sound bad, but a pat of butter, which is the amount you're more likely to use, only has 4 grams of fat. Only 0.5 grams of light mayo's fat content is from saturated fat, however. A pat of butter has 2.5 grams of saturated fat and only 1 gram of healthier monounsaturated and polyunsaturated fats. This is significant because saturated fat can raise your cholesterol, harden your arteries and cause heart disease or stroke.
Vitamins and Sodium
Condiments aren't the best source of nutrients, but they do contain tiny amounts of some. A tablespoon of light mayonnaise provides 20 times as much vitamin K and three times as much vitamin A as a pat of butter. Vitamin K helps ensure proper blood clotting and contributes to strong bones. Vitamin A is an antioxidant that benefits your eyes, skin, hair and nails. Light mayonnaise, however, is saltier than a pat of butter. A tablespoon of light mayo has 112 milligrams of sodium, three times the amount in a pat of butter. In fact, a whole tablespoon of butter has 101 milligrams of sodium.
Don't Use Either
If you're concerned about keeping your meals nutritious, your best bet is to avoid light mayonnaise and butter and replace them with healthier toppings. Avocado spread, low-sodium mustard or olive oil and vinegar can stand in as more nutritious substitutes on your sandwiches. Skip butter on bread and rolls, or top them with a light layer of jelly instead of a high-fat spread.
Maia Appleby is a NASM-certified personal trainer with more than 15 years of experience in the fitness industry. Her articles have been published in a wide variety of print magazines and online publications, including the Gale Encyclopedia of Nursing and Allied Health, New Moon Network and Bodybuilding.com.