Yes, most of the calories we get from plants are in some form of starch. Amylase and disaccharidases both are dedictated to starch digestion. While proteases are dedicated to protein digestion (ie Meat). In addition there are lipases for fat digestion, which can come from either plants or animals.
I never meant to indicate that there were not other creatures that fit the same profile, but the OP asked for indicators limiting them to the physiology.
The primary reason humans are the primary predators is the psychology of their large brain, the sentience there, the ability to create tools, figure things out, communicate with other humans and to use advanced intelligence. That part is unseen, so since it did not appear to fit the requested criteria, I did not use it.
The basic criteria mentioned also fits, more or less, several species of animals. The separating difference is the brain and intelligence. The description I gave confirms that a human is omnivorous – so are chimps and several other animal species.
Alien xenobiologists need not analyze our mandibular structure, nor break down the contents of our stomach acids, in order to determine that humans are omnivorous - they need only go to a McDonald’s.
Their evidence? The Big Mac[sup]TM[/sup].
This sandwich is a pile of globulous crap packaged as a fine balance of meat, grains, and vegetable matter in a conveniently portable form. They only gotta see us eat one to conclude “Those humans will eat anything.”