The Adkins diet has always been a mechanistic mystery to me, i.e. why it works. That said, I bet the first study to examine downstream consequences finds linkage to illnesses of uric acid and purine metabolism, like gout.
In an arguably oversimplified nutshell, it works on two bases:
1. A drastic reduction or elimination of carbohydrates will force your body to go in to a mode where it rapidly metabolizes fat for energy, since it can't get sufficient energy through ingested food alone.
2. Proteins and carbohydrates are metabolized at different rates. Proteins slowly, since the body breaks proteins down in to aminos, and the body uses them first for cellular regeneration and muscle development before they are broken further down in to starch, and eventually glucose. Carbohydrates are already halfway there. Sugars are right there. In any case, the body has to break proteins and starches all the way down to glucose before they can be used for either energy or fat storage. So, you can eat a lot more protein (and fat) calories that you can starch calories to supply a given basal metabolic rate.
I don't think that the Adkins diet in itself is particularly harmful to your system or puts you at greater risk of colon cancer. You have to have other nutrients, and fiber in your diet and you can get those with most vegetables without incurring a significant carbohydrate load, particularly with leafy green vegetables. The key is to eat enough of those to flush out your system.
I have a family history of celiac disease, with some family members unable to eat anything glutenous or anything very high in starch content. They have grown up on what we would call the Adkins diet their entire lives with no apparent ill effects. Myself included, at least so far.
