Some fast food fans may choose Subway over McDonald’s simply because they thought Subway provided them with a healthier option.

The study which looked at the eating habits of nearly 97 adolescents between the ages of 12 and 21 who bought food at McDonald's and Subway restaurants, and evaluated calorie and nutritional content, found that the calorie consumed were just as much in both places.
Both the outlets were at par when it came to dishing out fast food.
“If the true measure of a healthy restaurant is whether people actually consume a healthy meal there. If the healthy options do not look attractive, are not displayed prominently, are priced higher, or are offered with high-calorie side dishes, consumers may be less likely to choose those foods."
Source-Medindia