correct the two errors. less calories then the leading brand

Brief Explanations:

1. "Less" is used for uncountable nouns, but "calories" is countable, so "fewer" should be used.
2. "Then" is used for time - related or sequential context, while "than" is used for comparisons. Here, a comparison is made, so "than" should be used instead of "then".

Answer:

Fewer calories than the leading brand