SaltySeaBird: many UK and US citizens are low on magnesium, vitamin D and omega-3s (pref. long chain). These are all very important in diabetes, insulin resistance, obesity, mental health and numerous other inflammatory conditions.
This is largely due to restrictions in personal taste: we don’t eat much oily fish (sardines/ mackerel/ herring) with some bones, other seafood esp. molluscs (mussels/ snails/ oysters), seeds (flax/ pumpkin/ chia), cocoa or low sugar dark chocolate, bran (rice/ wheat), organic eggs from seed-fed and insect-eating birds (less soy, corn, grains).
When we go lower carb we tend to increase meat from land animals, o-6 rich/ o-3 poor nuts, calcium rich/ magnesium poor dairy, green vegetables, processed carb alternatives. This often worsens existing nutritional imbalances.
I have not read the ‘Blood Sugar Diet’ but hope it emphasises variety and the much neglected food groups I listed! Certainly these types of wholefood played a key role in the stone age and Mediterranean diets, and are arguably more what our microbiome evolved on.
HTH!