(1) Concern about healthy lifestyles grow in the mid-twentieth century as information on hygiene, disease and nutrition became plentiful. (2) People learned what practices spread sickness, how disease can be avoided, and what food was good for the health. (3) The results of unhealthy lifestyles also became clear to the population, so people started changing the way they lived. (4) This is why more and more people today are careful about eating the right food, getting enough exercise and seeing their health practitioner on a regular basis.
요기서 (2)에서 쓰인 spread, can be avoided, was 시제가 이해가 잘 안가요.