The food restrictions in the official HCG diet plan go back to Dr. A.T.W. Simeons and his research on the human digestive and metabolic systems. His fascinating book entitled Pounds and Inches offers penetrating insight into why obesity is a disorder born of modern civilization.
Dr. Simeons concluded that modern obesity is the result--largely--of routine meals, which are in opposition to how the human being was created to eat--only when hunger set in and only enough food until the hunger went away. Thus we moderns simply overeat, and for many of us that means the pounds incrementally add on, and on, and on until our physiques no longer resember our youthful trim.
In addition, Dr. Simeons noted that the human species entered this planet best suited to digest raw and unrefined foods, with the exception that Neolithic man did cook his meat over an open flame. Except for this prehistoric barbecued protein, early man (and woman) ate raw and unrefined foods.
Thus when Dr. Simeons pioneered his HCG diet drops plan for shedding weight, he simply reverted to what works best for the human being, and thus he proscribed (prohibited) refined substances, including sugars and starches and the foods that come from them. He also knew that copious amounts of water purge the system and keep it healthy (and less hungry), so he prescribed one-half to one gallon of water consumption everyday.
On the official HCG diet plan, you're not doing yourself a favor if you, say, eat 500 calories a day of donuts. Wrong! That won't work, and in fact, such consumption will only make you hungrier to the point that you'll probably gorge out.
On the HCG diet plan, you need to stick to the regimen, but if you find yourself cheating on one occasion, just follow this advice.