Researchers from the Cornell University wanted to find out what people who are naturally thin, and have never struggled with weight problems eat.
Almost a 10th of the respondents were vegetarian and nearly a fifth said they did not take alcohol. But despite their healthy habits, almost half said they did not diet.
While dieters might be tempted to skip breakfast, it seemed slim people hardly ever missed a meal. Only four percent of people said they did not eat breakfast.
"One important take-away from this study is that a very high rate of slim people actually eat breakfast instead of skipping, which is consistent with previous research on the importance of breakfast," said lead author Anna-Leena Vuorinen.
"But what stands out is that they not only ate breakfast, but ate healthy food like fruits and vegetables," Vuorinen added.
The study found the most common breakfast items consumed by slim people were fruits (51 percent), dairy (41 percent) and cold cereal /granola (33 percent).
They also ate bread (32 percent), eggs (31 percent), hot cereal (29 percent), and coffee (26 percent). When it came to snacks, fruit and nuts came out top.