According to this Wikipedia article, Starship will take on average 115 days (3.8 months) to get to Mars and 150 days maximum (4.9 months).
with an average trip time to Mars of approximately 115 days (for the nine synodic periods occurring between 2020 and 2037).
And according to this NASA article, an astronaut in one month in orbit loses the same amount of bone mass as an elderly women does in one year. Furthermore, a few months in space leads to an increased risk of bone fractures when load is applied to their bodies. And surely colonists on Mars will be doing a lot of physical work.
Although healthy astronauts did not develop osteoporosis during their four- to six-month stays on the space station, the levels of bone loss documented were still enough to raise the concern for an increased risk for fracture when astronauts’ skeletons are subjected to applied loads with working, lifting or falling.
After astronauts return from the ISS, they feel dizzy and nauseous. So the passengers of Starship will feel the same way returning to an environment with 1/3 of Earth's gravity after a 4 month journey in micro-gravity. This is a passage from this article.
Even after a ten-to-fourteen-day mission to space, the return is dramatic. Your balance system is turned upside down, and you feel very dizzy. When you stand up for the first time, you feel about five times heavier than you expect. All of this can be unsettling, and nausea is not unusual.
Of course they are returning to Earth which has stronger gravity than Mars but the side-effects are the same nonetheless.
Even with exercise, micro-gravity is a big concern that leads to many health problems and the fact that their are 100 people on-board makes it an even bigger concern.
So my question: How will SpaceX accommodate its passengers from the harmful effects of micro-gravity?
Side Note: I don't expect a proper answer with professional citations, any source where Elon Musk or the SpaceX team bring up this topic is sufficient.