You still are what you eat, in part.
Sorry, but no. :)
If you're eating primarily beef, then parts of the proteins that you're built of are parts that used to be a cow, no?
Yes : a cow is an organism, composed of organs, which are composed of tissues (Eng ?), which are composed of macro-molecules (among them : proteins), which are composed of (simpler) molecules (among them : amino acids), and these last ones are shared by all (known) forms of life on Earth (and maybe beyond).
Some macro-molecules may be specific (existing only in one species), and no species use all the basic molecules (amino acids, fatty acids, simple glucids, etc.), but most species share most of these basic molecules.
All (known) forms of life on Earth share the same genetic coding molecules : DNA and RNA ; all these coding molecules code for proteins (polypeptides) made of the same range of peptides (amino acids).
To take an image : it's like you're thinking that with the components of a (brick-made) bridge, you can only build a bridge ; wrong, if you unbuild the (brick-made) bridge, you get bricks, and with these bricks you can build a tower (for instance).
But you're saying that there is a process of conversion, right?
Kind of : while digesting your body "unbuild" some macro-molecules (the "bridge", here : a piece of beef or mango), to have simple(r) molecules (amino acids, glucose, etc.), to use to build a human (the "tower").
So whatever you take the components from, may it be any form of life on Earth (animals, vegetals, mycetes, bacterias, etc.) and even minerals (air, water, salts, clay, etc.), what your cells (driven by your DNA) will build is some human (macro-molecules, tissues, organs, organism).
Another scoop : the glucose molecules from the mango are the same in you blood or in the cow's blood.
And the albumine (a kind of protein) in your blood is maybe not exactly the same but quite similar to the one in an egg, (and probably in a cow's blood, but that should be checked).
And we're only speaking of matter here, not to mention the consciousness or emotions that carry over when eating something.
Indeed, I'm writing here from a materialistic PoV.
And generally what you're eating is dead (no more consciousness or emotions, according to the materialistic PoV)...
If you eat oysters (without chewing them), they may live a few hours in your stomach, dying slowly burnt by the chlorhydric acid your stomach produce... but that's before you digest them.