Is it true you shouldnt eat before swimming?

What do you mean by "swimming". Digestive processes shift circulation to the gut that active swimming (a race) would need for muscle activity. If you mean just getting into a pool and splashing around some I wouldn't worry about it. If you want to swim well and to a distance, I would avoid eating before the activity.

It would be helpful to not eat before competitive swimming. For recreational swimming having a light meal before the activity would not matter. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.