primarily as an energy source. Under normal dietary conditions, most tissues in the body use
carbohydrates, in the form of glucose, for fuel. There are exceptions such as the heart which rely
primarily on fatty acids for fuel.
Carbohydrates are generally subdivided into complex and simple carbohydrates. All
carbohydrates are formed from the simple sugars glucose, fructose and galactose, called
monosaccharides. Monosaccharides combine into chains of two, called disaccharides. As
monosaccharides form into longer chains, they are called polysaccharides or simply starch,
which is a chain of hundreds or thousands of glucose molecules attached to each other.
The term ‘complex carbohydrates’ refers to starches such as breads, pasta, potatoes, rice,
and all grains. Simple carbohydrates refer to sugars such as table sugar (sucrose), fructose and
fruit. Carbohydrates can be further delineated based on the Glycemic Index (GI) which is
discussed below.
Digestion of carbohydrate
Despite dietary differences between carbohydrates, almost all ingested carbohydrate will
enter the bloodstream as glucose, raising blood glucose levels. Each gram of dietary
carbohydrate appears in the bloodstream as 1 gram of glucose. A very small amount of ingested
carbohydrate (approximately one percent) will enter the bloodstream as fructose (fruit sugar).
Once in the bloodstream, glucose has a variety of fates. It can be burned immediately for
energy by most tissues of the body or stored as glycogen (a long chain of glucose molecules
attached to one another) in the muscle or in the liver for later use. If an excess of carbohydrates
is consumed, glucose can be converted to fat in the liver (a process called de novo lipogenesis) or
pushed directly into the fat cell as alpha-glycerophosphate.
How much carbohydrate can be eaten per day?
Chapter 5 established that the body can survive indefinitely on a diet completely devoid of
dietary carbohydrate (assuming protein and vitamin/mineral intake is sufficient). However, from
a practical standpoint, it is nearly impossible to avoid all sources of carbohydrate in the diet.
Additionally, a diet completely devoid of carbohydrate foods may rapidly become monotonous.
The question to be answered is how many grams of carbohydrate can be consumed without
interrupting ketosis.
Although up to 100 grams of carbohydrate will allow ketosis to develop, it would be rare to
see ketones excreted in the urine at this level of intake. Since the only measure of ketosis
available to ketogenic dieters are Ketostix (tm) carbohydrates must be restricted below this level
if ketosis is to be measured. As a general rule of thumb, dietary carbohydrates should be below
30 grams per day for ketosis to be rapidly established and for ketones to be lost in the urine.
However, this value varies from person to person and depends on other factors such as
protein intake and activity, which allows individuals to consume relatively more carbohydrate
without disrupting ketosis.