The rules on the UTMB web-site (http://www.ultratrailmb.com/page/16/Rules.html) say
"2. Refreshment posts have been supplied with drinks and food to consume on the spot.
Only plain water (excluding other drinks) is destined for filling-up water bottles or bags. Each runner must be sure to have, upon leaving each refreshment post, the quantity of water and food necessary for them to reach the next refreshment post."
which does seem to say it applies to food too. (Last year I got a bit of a look from a marshall when leaving a checkpoint with a handful of biscuits, but they didn't attempt to stop me, possibly because I was only a couple of minutes inside the cut-off...)