From the United Biscuits website:
The Jaffa Cakes brand team scored a McVitie's first in July 2000, when they signed a sponsorship deal with Manchester United. Jaffa Cakes became one of Man Utd's eleven 'platinum' sponsors but the only one focussing on kids in the UK. Jaffa Cakes were already enjoyed by the team and were officially launched as the teams favourite half time snack. The campaign's success was based on the product truth that Jaffa Cakes are low in fat and high in carbohydrates and so are a great energy provider.
It was for this very reason that Sven announced that Jaffa Cakes would join the England squad in Japan for the 2002 World Cup as part of their training diet. The publicity was amazing, culminating in a spectacular story of a McVitie's Jaffa Cake being found with the face of David Beckham, the team captain, on it!!!
In 2006 the fact that each Jaffa Cake is only 1g of fat has featured in the new advertising.
So once again you are talking out of your @rse.