In the view of the UK advertising body ASA, claiming a health benefit is immediate may exceed the flexibility to an approved health claim. In casu, ASA argued the words ‘feel the burst’, ‘fast’ and ‘direct’ accompanying the product name Dextro Energy would imply an instantaneous increase in energy levels. Included in the advertisement was the authorized claim that vitamin C contributes to the reduction of tiredness and fatigue. But according to the ASA opinion this does not extend to a sudden energy boost. Dextro also argued that the words “feel the burst” specifically related to a burst of flavor. This was not upheld by ASA.
UK Advertising Standards Authority - Ruling on Dextro Energy GmbH & Co KG (13 February 2019) - link