While working three years at a relatively low-movement job, I managed to avoid gaining weight, but all the same accumulated a bit of fat in places none too flattering (a visual discomfort made worse because I had little fat elsewhere on by body). I started a no-carb diet (commonly known as the 'Atkins Diet') in mid-June, and two weeks later, that normally hard-to-eliminate fat is gone now.
The introductory line to the Atkins Diet Wikipedia article sums the science of the program up quite nicely: "The Atkins diet involves limited consumption of carbohydrates to switch the body's metabolism from metabolizing glucose as energy over to converting stored body fat to energy." I hadn't realised until now that the body's metabolism phases were so simple, yet when looking back at the evolution of human diet, this makes perfect sense.
One must remember that before the Neolithic age (around 10,000 BC), processed carbohydrates were almost non-existent in human eating habits. Until then our diet consisted mostly of meat, berries, roots, fruit and other greens that could be consumed 'as found' from their plant source. The agriculture developing around then produced wheat (bread and beer), rice, maize and later potatoes (south America only until the 16th-century colonisation there) - all of these are the main source of our modern carbohydrate-rich diets. So, in considering the 200,000-year evolution of the modern human, one can easily assume that the diet most adapted to the human body is a low-carbohydrate one.
The consumption of carbohydrate-rich food (and sugars, but carbohydrates in reality are sugars), transformed by our digestive process into glucose, triggers a production of insulin in the human body; insulin 'deals with' carbohydrates (and sugars) in the bloodstream by forcing fat tissue to take up excess glucose, and by transforming glucose into glycogen that is stored in muscle and liver. So, in this light, could insulin be considered almost as a defence mechanism against 'modern' eating habits?
If there is little or no glucose present in the bloodstream, the body enters a state of 'ketosis', or when ketone bodies produced by the liver (because of a lack of glycogen therein) begin breaking down fats into a form ('good' cholesterol and glycogen) usable by the human body. The state of ketosis is seen as almost abnormal today, but could it once have been the standard for the human metabolism? Or, in other words, is the Atkins Diet simply a return to our eating habits of 10,000 years ago?