Hi,

Single sugars with a hemiacetal or hemiketal can convert between alpha and beta in a process known as mutarotation - that is you can consume beta D glucose and it will naturally interconvert in solution between alpha and beta (The beta hemiacetal just happens to be more prevalent as it is slightly more stable)

Once your body stores sugars as complex carbohydrates, the hemiacetal becomes a sugar acetal and the alpha beta configurations are set and cannot be interconverted - however they can be set as beta or alpha.

So you can consumer beta glucose and convert it to alpha glucose in a carbohydate polymer, because the glucose ring can be opened and closed before incorporating it into a sugar, changing it from beta to alpha. You can also have sugars where the glucose linkage is beta, where this switch did not occur.

Please let me know if this is unclear.