The sachets contain sugars which occur naturally in food. The contents of each FODMAP packet is equivalent to eating the following:
Fructose packet = the same amount of fructose as 2 medium-to-large apples*
Lactose = the same amount of lactose as drinking 2 cups of milk*
Inulin = the same amount of inulin as eating 1-1.5 average Jerusalem artichokes**
Sorbitol = the same amount of sorbitol as eating 2 servings of prunes (actually it's only 1.7 servings of prunes but we'll round up)***
Therefore, if you feel any discomfort when eating these foods, you may choose to skip this test or you can elect to use a smaller amount. Note that if you use a smaller amount than the entire packet, your results may not be accurate.
*Source: United States Department of Agriculture
***Source: Stacewicz-Sapuntzakis M, Bowen PE, Hussain EA, Damayanti-Wood BI, Farnsworth NR. Chemical composition and potential health effects of prunes: a functional food? Crit Rev Food Sci Nutr. 2001 May;41(4):251-86.