First be very careful in trying to suppress your appetite in such an unhealthy way. Not only is that bad for you but your breastmilk production as well (not the caffeine but the lack of calories).
Here is a piece of an article about caffeine & breastfeeding, the link is at the end. As long as baby is not upset by it, you are good to go. Enjoy your cup of coffee. Congratulations on breastfeeding!
"Caffeine is approved by the American Academy of Pediatrics for use in breastfeeding mothers. Per Medications and Mother's Milk (Hale 2002, p. 100-102) caffeine is in Lactation Risk Category L2 (safer); milk levels are quite low (0.06-1.5% of maternal dose) and usually peak 1 hour after ingestion. One study has indicated that chronic coffee drinking might decrease iron content of breastmilk (Nehlig & Debry, 1994)."
http://www.kellymom.c
om/health/lifestyle/caffeine.htm
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