This break-down process is called “hydrolysis.” It is mostly used in commercial bread production.
While long fermented traditional doughs allow lots of time for enough starch to break down into the sugar for the yeast to feed on; in modern bread, Alpha Amylase is included in bread improvers to make the process faster for commercial enterprises.
When making bread commercially, yeast is given either sugar, or sugar that results from Alpha Amylase acting on the starch in the flour. Some argue that industrially, alpha amylase is better than sugar because it releases sugar energy at a rate proportional to the rate that the yeast needs it. But the alpha-amylase damages the flour, by breaking it down to get the sugars out. Consequently, flour that has alpha-amylase act upon it holds less water, so more flour must be used, thus pushing the baker’s cost up.
Using too much Alpha Amylase in a bread dough can make the dough sticky (as it hasn’t been able to absorb enough water), and can lead to undesirably large gas-caused holes in the bread, because the yeast was too active. The resultant crumb will also be somewhat sticky and harder to slice. In industrial bread plants, bread that is sticky or gummy to slice can lead to mangled slices in pre-sliced loaves of bread.
Alpha-amylase activity is measured using a “falling number” scale to indicate what kind of product the flour will be good for. Wheat for industrial baking purposes is usually sold with an indication of its “falling number” measurement. If a wheat has “sprouted” (owing, for instance, to damp times at harvest), it has more alpha-amylase in it, which results in lower “falling numbers.” Pasta makers want wheat with high falling numbers, to produce a quality product — sprouted or damaged wheat, with low falling numbers, can result in pasta that is harder to form, more brittle in drying, and gets softer than desired at suggested cooking times.
Malt is rich in alpha amylases, but many prefer to use a fungal version of alpha amylase (usually derived from the fungus aspergillus oryzae), or a bacteria such as “Bacillus subtilis.” While some alpha-amylase enzyme is present naturally in the outer layers of the germ of wheat kernels, far more is produced when the kernel germinates.
Alpha Amylase inhibitors, aka AAI, also called “starch blockers”, inhibit the enzyme’s activity. Commercially these are often made from protein from kidney beans (white or red.)
Alpha Amylase has been used in making chocolate syrup since 1929.
Many bakers become hypersensitive to Alpha amylase owing to over-exposure. A study led by Dr Mark Nieuwenhuijsen, from the Imperial College of Science, Technology and Medicine, London, in 1999 concluded that bakery workers with high exposure to Alpha amylase in flour dust in the mixing areas of bakeries also became more susceptible to developing asthma. 
 There is a gene that produces amylase enzyme in saliva, which enables starch to be broken down into energy for the body. Researchers reported that primates such as chimpanzees, which live on protein and fruit, have two copies of the gene. Humans have several more copies of the gene, enabling them to process starch more efficiently. Interesting, human groups which eat more starch acquire more copies of the gene. The researchers also pondered whether access to this additional “fuel for the body” in the form of starch, thanks to the amylase enzyme, enabled the development of larger brains in humans. cf: Perry GH, Dominy NJ, Claw KG, Lee AS, Fiegler H, Redon R, Werner J, Villanea FA, Mountain JL, Misra R, Carter NP, Lee C, Stone AC (2007). Diet and the evolution of human amylase gene copy number variation. Nature Genetics 39: 1256-1260.
 BBC. Bread additive ‘raises asthma risk’. 23 February 1999. Retrieved April 2008 from http://news.bbc.co.uk/2/hi/health/284451.stm .
Dexter, J.E. and N.M. Edwards. The Implications of Frequently Encountered Grading Factors on the Processing Quality of Common Wheat. Canadian Grain Commission, Grain Research Laboratory, Winnipeg, Manitoba, Canada R3C 3G8. Contribution No M212. Presented at the 101st Association of Operative Millers (AOM) Trade Show, Nashville, Tennessee, May 1997.