Most of those problems in the US are caused by lifestyle, and can't really be changed without behavioral modification. And a lot of our health issues are a matter of poor access to healthcare.
This assumes that the fundamental nature of human beings can't be changed, which is the presupposition that genetic engineering denies.
The entire point of genetic engineering is to try to engineer people at the cellular level. A fanciful example would be modifying human metabolism to be more similar to those of birds that consume most of their calories in the form of simple sugars. Humans can't eat a diet of 100% sugar and remain healthy, but other animals can. It may be possible to change that fact, if we know how to edit our genes.
Are you saying you could see sugar being somehow folded into the many different proteins that make up the vast number of tissues in our bodies. Or are you saying our tissues could be constructed out of sugar crystals instead?
Proteins can be synthesized from sugar as a carbon source. We know this because there are bacteria that can survive and reproduce with no nutrients in their environment other than glucose.
In fact you don’t even need sugar. Carbon dioxide and water alone are sufficient. Plants produce their entire biomass using nothing but carbon dioxide, water, sunlight and trace elements from soil.
Amino acids and proteins don’t occur without life. Living creatures have the ability to synthesize all amino acids and proteins from simpler compounds.
