The actor traded in Muay Thai training for six-hour daily dance rehearsals to compete in "Dancing With the Stars." Last month, Van Der Beek, 42, was eliminated just a week before the show's final episode of the season, People reported.

But all that training left a mark on Van Der Beek's physique, according to a post comparing his before-and-after photos.

"Fight training vs. dancing...," he wrote on Instagram. "Id been training in Muay Thai three days a week for about six months (for the next project Im writing) when I hit pause to dance six hours a day. Now I can rhumba," he wrote.

Fans were astonished by the transformation.

"Both cut but you can see dancing really defines everything. Especially when you worked as hard as you did! In every way you are a huge advocate for dance @vanderjames !!!," a commenter wrote on Instagram.

Of course, physical activity alone won't get anyone a six pack, and one fan asked Van Der Beek about his diet.

Van Der Beek explained he followed a plant-based diet for most of the day due to rehearsals.

"Lot [sic] of fruit, vegetables, lot of smoothies, salads. I danced early in the day so pretty much ate vegan until dinner," he wrote. "Had to keep it light fare because we didnt really take breaks. Not so much a diet... more like only wanting to eat what I knew would make me feel good under the work load."

Still, dancing is a good, and overlooked, workout. A one-hour aerobic dancing session torches nearly 500 calories for the average 175-pound person .