There is a lot of confusion, or at the least lack of clarity, about the role of fruit sugars in 'fruit fast' diets and interventions (see Juicemaster) - and confusion about the relative merits or problems of commercial fruit juices and processed food 'fruit' products.

An article in Am J Clin Nutr October 2007, (which might of course be superseded by now by other research) does give some pointers to a clearer understanding of the issues.

Particularly, key extracts from the article which state that ...

1. "When ingested by itself, fructose is poorly absorbed from the gastrointestinal tract, and it is almost entirely cleared by the liver".

... this provides support for the use of unprocessed fruit, or fruit juices, in diets. The key phrase is 'when ingested by itself' - which means that fresh fruit/ fruit juice has little or no role in causing either diabetes or obesity. On the other hand, when ingested with other things, this is not necessarily the case.

So ... the processed food industry, which combines fructose with a range of other sugars and 'additives' is the problem. Not the fructose.

2. "Fructose is an intermediary in the metabolism of glucose, but there is no biological need for dietary fructose".

In which case the use of large amounts of High Fructose Corn Syrup in processed foods is i) unnecessary, ii) just adds to our addiction to sweetness, and iii) is counterproductive to health (see the full article for details).

3. "Fructose is absorbed from the gastrointestinal tract by a different mechanism than that for glucose. Glucose stimulates insulin release from the isolated pancreas, but fructose does not".

So ... as long as fruit/fruit juice is unprocessed and pure, it has very little or no role in interfering with insulin production, or diabetes.

Quotes from:
Am J Clin Nutr October 2007
vol. 86 no. 4 895-896

http://ajcn.nutrition.org/content/86/4/895.full