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1. Alcohol serves no useful purpose to a healthy body. There are less positive factors than negative ones. The effects of alcohol remain in the body for a while and all these affect better performance of the body. Climbing mountains requires maximum performance.
2. Drinking strains your kidneys because water in your body is directed into your kidneys to metabolize the alcohol.
3. Your mental capacity is limited by the presence of alcohol in the body. The brain receives less glycogen and your general alertness is reduced - a factor that inhibits your training.
I used a few facts on the deleterious effects of alcohol from this source:
but there are numerous other links you can read:
There are some benefits to consuming alcohol but, in general, the negatives effects outweigh the positive ones.