Eating evidence is never a good idea. It has a very low success rate in actually thwarting a police investigation, and it can significantly increase a suspect's exposure to criminal charges.
It may be funny to see characters like those in the cult classic "Super Troopers" eat massive quantities of illicit substances in a frantic attempt to not get busted, but the reality is even uglier.
What are some real-life consequences of eating evidence?
Evidence Tampering Charges
Because eating evidence may mean taking something incriminating and then eating it, you may be slapped with an evidence tampering charge. In New York, tampering with physical evidence with intent to keep it from being used in an official proceeding (read: any criminal hearing or trial) is a felony.
Even if law enforcement may not be able to prove that you were attempting to eat evidence with the intent of keeping it from being used at trial, there are lesser criminal tampering charges that only require that you intentionally tampered will someone else's property. Many of these tampering offenses are misdemeanors and can mean months in jail, in addition to any other charges.
Obstruction of Justice
Depending on what evidence you tried to eat, you may be experiencing some blockage, but obstruction of justice is likely to be a much more pressing problem. Obstruction of justice covers just about any situation in which you impede a peace officer from doing his or her job, and that includes investigating crime and collecting evidence. You can be charged with obstruction simply by not obeying an officer's orders to remain seated in a car (just ask Reese Witherspoon), so chewing up and swallowing evidence isn't too far off.
Monitored Bowel Movement
Just because you've swallowed something doesn't mean it's gone. If police suspect that you've swallowed evidence of a crime, they may just stick around and watch you poop. This is more common in drug smuggling cases, but depending on what evidence you ingested, there may be sufficient proof to have your next bowel movements monitored.
Internal Injury and Death
When you swallow anything that isn't food, you run the risk of serious internal injury and possibly death. With illicit drugs, consuming large amounts to conceal them from detection isn't likely just to make you "super high"; rather, you risk overdose and all of its associated complications.
So don't make a bad situation worse; don't eat evidence.