Well-known sources of carbohydrates in the diet are the starches, such as cereals, potatoes, and pulses. A specific role for carbohydrates in biotransformation is not likely. The effects of dietary carbohydrate manipulation are likely because of generalized effects on intermediary metabolism, such as caloric effects and hormonal alteration effects. Animals use glucose as the principal carbohydrate and the level of blood glucose and amounts available to the animal’s organs are closely regulated. It is well known that when carbohydrate intakes are high, any excess glucose is first converted to glycogen for storage, and when those stores are filled, it is converted to fat, in which form the storage is probably unlimited. When energy is required, glycogen stores are utilized, followed by gluconeogenesis concomitant with mobilization of fat stores.
High intakes of sugars, such as glucose, sucrose, or fructose, increase the duration of phenobarbital-induced sleep in rodents, and the longer sleeping times are correlated with a decreased metabolism of the barbiturate. High-sucrose diets as compared with starch, potentiate the lethal reaction to benzylpenicillin because of lower rates of detoxification of its toxic products. Also, rats fed high sucrose or glucose plus fructose have lower levels of cytochrome P450.
Carbohydrates affect genes because the structure of the genetic material, deoxyribose (DNA) and ribose (RNA), is derived from carbohydrates. Glucose as the precursor of glucuronic acid plays a role in Phase II detoxification reactions, which are crucial to the detoxification process.
In addition, diets contain other carbohydrates such as celluloses and other polysaccharides derived from plant walls. Fiber plays an important role in maintaining gastrointestinal tract function and health. Dietary fiber plays a role in the metabolism and deposition of lipids, and dietary fat and fiber affect chemical-induced colon cancer. Usually, fat has little effect when dietary fiber is high but increases tumor incidences when fiber is low.
Calorie restriction also has been found to exhibit lower oxygen consumption, increased insulin binding, and alter energy metabolism through changes in enzymes of glycolysis, gluconeogenesis, and lipid metabolism. The combined effect of metabolic effects and lowered oxidative stress has led to the speculation that calorie restriction may decrease age-associated enzyme degradation. Dietary studies have shown that unrestricted feeding decreases hepatic cytochrome P450, increases aflatoxin B1 activation, increases aflatoxin binding to DNA, and decreases in vivo detoxification of this carcinogen.