Added sugars: glucose and fructose differ and here is why

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0130280

Pure glucose do not exist in the wild. Other simple sugars are present in fruit, honey, and milk. They are frequently disaccharides like lactose (Glu-Gal), saccharose (Glu-Fru), so their hydrolysis leads to glucose, galactose or fructose.
Glucose is less sweet than fructose but is rewarding brain centers, fructose is less rewarding but differ in the metabolic pathway and galactose is prooxidant.

http://journals.cambridge.org/download.php?file=%2FBJN%2FBJN96_01%2FS0007114506001772a.pdf&code=840deec832a43919b5d589f01343f27c

Fig. 1. Changes in ¹³C:¹²C in expired CO₂ in response to exercise with ingestion of placebo and ¹³C-labelled hexoses (means and their standard errors; n 6). ‡Values were significantly different from those for glucose and fructose (P<0 fructose="" galactose.="" glucose="" placebo="" span="">

http://link.springer.com/article/10.2165/00007256-200029060-00004

About  galactose:
"In summary, the importance of normal galactose metabolism was recognized well over 30 years ago when researchers began their pioneering efforts on the four enzymes of the Leloir pathway (4, 25, 51, 52). Since that time an enormous amount of biochemical, kinetic, and structural data has been generated on these fascinating enzymes. Interestingly, in the past it has been speculated that enzymes within a given metabolic pathway evolved from one another because of the need to accommodate similar substrates (53). Clearly this is not the case for enzymes of the Leloir pathway. Indeed, questions remain regarding the evolutionary history of this important metabolic cycle."

http://www.jbc.org/content/278/45/43885.long