The claim that the "Freshman 15 is real", is a widespread phenomenon that is largely a myth, as shown by the research from the NIH article. In the random sample study conducted by NCHA, with a group of 582 freshman that were surveyed, they suggested while weight gain is common among college freshman, it is not as dramatic as gaining 15 pounds, as commonly believed. Instead, the average weight gain is closer to 2.7 pounds. Contributing factors in include changes in eating habits, frequent snacking, larger meal portions, and decreased activity. Fascinatingly, NIH reported there was no relationship between weight change and race or ethnicity and that males tend to gain more weight compared to women, but gaining 15 pounds is an exagerration. To ensure the validity of this claim, I cross-checked by looking up similar studies, and I came across "The Freshman 15 is a Dangerous Myth" from U.S. News. They stated that "reserach suggests the average amount of weight gained is around 2-5 pounds," reinforcing the idea that the idea of freshman 15 is exagerrated and isn't the case for every single college student. These findings show that weight gain is moderate and various from person to person and is based on individual lifestyle choices.
https://health.usnews.com/health-news/blogs/eat-run/articles/the-freshman-15-is-a-dangerous-myth