**5. Discussion**

Obesity pandemic is a great concern for not only health professionals but lay people. Because of such concern, weight loss diets often recommended are the restriction of either carbohydrates or fats. Low fat diets were popular in late 20th century, but carbohydrate restriction became popular in recent years. The proponents of carbohydrate restriction claim that this diet decreased insulin secretion which causes elevated release of free fatty acids from adipose tissues and elevated fat oxidation and energy expenditure. The restriction of carbohydrates was reported to decrease body fat more than restriction of dietary fat [28–30].

On the other hand it is well known that glucose is needed for many brain functions. Although neurons can use lactic acid astrocytes need glucose, which is degraded by glycolysis. ATP produced during glycolysis is used for the uptake of glutamate released from activated neurons [13, 31–33].

Since the administration of glucose or sucrose improved memory functions stated above, we must pay attention to maintaining good brain function in choosing carbohydrate restricted diets.

Glucose ingestion increases blood glucose levels, further insulin levels. Burtman's group showed that insulin is needed for the transportation of tryptophan from blood to brain [34, 35].

Tryptophan is converted in the brain to serotonin, further melatonin [36].

**Figure 9** shows that tryptophan absorbed from the intestine is transported to the brain in the presence of insulin. 5HT; serotonin.

Serotonin is important for many brain functions such as emotion, feeding, sleep resilience or satiety. We showed that increase in serotonin by intraperitoneal injection or by infusion into the hypothalamus of tranylcypromine resulted in inhibition of feeding (**Figures 7** and **8**).

Thus, glucose administration indirectly affects brain functions by increasing the concentration of serotonin in the brain.

Finally we should not forget the possibility of increased pleasure, thus increased motivation due to the stimulation of pleasure centers such as Nucl.Accumbens by sweet taste of sucrose as reviewed by Berridge and Kringelbach [37].

**Figure 9.** *Tryptophan transport from blood to brain.*

*Roles of Glucose and Sucrose Intakes on the Brain Functions Measured by the Working Ability… DOI: http://dx.doi.org/10.5772/intechopen.99203*

**Figure 10.** *Brain areas related to the stimulations by taking palatable foods.*

**Figure 10** shows a schematic representation of brain areas stimulated by palatable foods such as sucrose.

Sucrose applied to the taste buds on the tongue stimulates afferent fibers of cranial nerves such as IX or VII, which send informations of the taste to sensory areas of the brain. The stimulations of the taste area further activate Nucl.Accumbens, releasing dopamine and the periaqueductal gray in the midbrain, releasing βendorphin. Such stimulation may enhance the motivation [38, 39].

## **6. Conclusion**

Since brain needs glucose for variety of functions, attention must be paid to glucose when various diets related to glucose administration are discussed.

#### **Conflicts of interest**

There is no conflict of interest for any author.
