I am not convinced that colon cleansing is really medically helpful. If you really are, you should probably direct this question to the people providing the colon cleanse. Here is what WebMD has to say about colon cleansing: http://www.webmd.com/balance/natural-colon-cleansing-is-it-necessary They do not seem to suggest that any diet is particularly necessary pre-cleanse.
To avoid contamination in other experiments.
There is no reason to avoid having a legal marriage before a religious ceremony. Many couples do this in order to gain the marriage benefits.
Avoid aspirin, alcohol, vitamin E and certain medications before you think about having a tummy tuck operation. Your doctor might also want you to not eat certain foods before the operation.
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To avoid having bike crashes, look for traffic. Try to see situations before they happen. Wear bold colors and reflectors.
If one is in Rome one should try to avoid having their picket picked and certainly try to avoid getting run into by a Vespa.
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You should avoid having cheap motorcycle tires on your bike to prevent possible crashes and lower performance. Cheap tires can easily pop and put the rider in danger.
You NEED to avoid any pets or loud noises.
There are multiple ways to avoid pregnancy, communication with your partner is important. Before having sex with your partner you should use a condom, if you forgot there are multiple ways to prevent pregnancy, you should inform a doctor for options.
To avoid danger from an underground cable or wire, you should call before you dig. That way you do not accidentally get hurt.
Young children showing signs of intolerance should avoid milk products; infants should switch to soy-based formula.