I hate to have to say this of someone who is working at my old medical school, but Prof Feldman is an anaesthetist, not a nutritionist, so he is a bit off his specialty here, and it shows. I was taught the 'full breakdown into amino-acids' hypothesis at Westminster back in the 60s, but knowledge has moved on considerably since then.
It is known now that large chunks of foods (macromolecules) can get through into the bloodstream, and can set up various adverse reactions in the host.
It is also known that some pesticide residues are toxic to some individuals.
It is known that organic foods contain more micro-nutrients than industrially produced foods.
It is known that some people are adversely affected by some additives, mainly coal tar dyes and derivatives thereof.
It is known that some highly processed foods are deficient in some micronutrients. It is known that a growing number of people are intolerant of common foods.
There is a vast body of literature out this, under the heading of Clinical Ecology. The problem, as with all natural medicine, is that nobody can get a patent out of it, and randomised controlled double blind clinical trials are both expensive and very difficult and complex, so it is not studied as intensively as patent medicines. There is also a presumption among my colleagues that exclusion diets are difficult (they are not), that patients are reluctant to do them (they are not) and that they are not often effective (they are not), and that to do real medicine you need to give someone a pill.
For anyone who is really interested, British Society for Ecological Medicine is a good place to start. The book to read is Environmental Medicine in Clinical Practice (Anthony, Birtwistle Eaton and Maberley) BSAEMN Publications 1997.
"Dr Lawson regrets that he cannot enter into private correspondence".
Hope this helps.
PS I think it is closer to say that we are what we think we are, than to say we are what we eat.