The 23-year-old Grammy-winning singer said he does not work out much and is depending on diet control, reported People magazine.
"I've just not eaten like a pig anymore - that's what I'm doing, basically," Smith said.
"I have been the last week," the "Stay With Me" hitmaker added, when asked about his excesses regime.
Last year Smith credited nutritional therapist and author Amelia Freer for his slimmer frame and healthier outlook towards life.