I would like to point out that no one has presented any stats differentiating between all these sciences. There's a reason for this, I don't think there are any. The fact is, medical schools DO have statistics by major class (like biological sciences, physical sciences, humanities, social science, etc). I would imagine that these stats exist in this format because medical schools like grouping majors this way.
Also many schools don't offer biochemistry as a major, but as a concentration. Some offer the coursework without the designation on the transcript at all.
I would imagine that biochemistry would be lumped into chemistry and the biological sciences. That being said, I really dont think there is a huge difference between a chem major and a biochem major, or a bio major and a biochem major (since biochem lies intermediate to those two, depending on curriculum structure).
If you love biochem, by all means take it, but take any advice that "this major is known to be hard and will help you get into medical school." More often than not, using this as a primary reason will leave you unhappy and with a poor grades. Just do whatever interests you, when it comes admissions time, the difference between the science majors is minimal.