142km fasted this morning. Slightly cooler but still suffering at 43C real feel! There is some evidence training fasted (ie: no food intake before or during) or glycogen depleted (starting training with low carbohydrate stores) may stimulate better training adaptations and increase fat metabolism. However, there's little evidence to suggest this has a subsequent effect on performance, although much research is ongoing in the area.
Training fasted does have some drawbacks - increased perception of effort, lower self-selected pace and increase risk of illness. If you do practise this strategy, stick to low intensity sessions and limit to 1-2 per week.