Nutrition Support Blog: Influence of TPN on Appetite and Food Intake
October 29, 2013
I have found that the answers you discover in the medical literature can be influenced by the way that you phrase your search question. One example of how your question can be the crux point of your search is what happened when I looked for information about the effects of parenteral nutrition on appetite.
I was surprised to find research documenting that parenteral nutrition, even when it provided full nutrition needs, had limited impact on appetite or satiety scores.1,2 If I had stopped my search after the initial survey I might have concluded that it was fine to continue full parenteral nutrition (PN) or enteral nutrition (EN) while we evaluated the adequacy of a patient’s oral intake.
However, when I investigated further I found research that served as a reminder that in humans, appetite, hunger and satiety are not necessarily the same as the physiologic need for food intake. Research as early as 1974 documented that even when people on PN reported “ravenous” hunger, they were only able to consume small amounts of food when able to eat ad lib.3 One study reported that even healthy people decreased voluntary oral intake within 24-48 hours of parenteral nutrient infusion, “by an amount that closely compensated for the infused calories”.4 Other research documented that even when patients reported moderate hunger, food intake was less than 600 calories/day and there did not appear to be a major influence of changes in lipid:CHO ratio on food intake.2
My clinical experience suggests that in the “real world” hospital setting, PN or EN may have an even greater impact on food intake. Patients may be frightened, sad, nauseated, constipated, in pain or all of the above. In nearly all cases they are receiving food that is different than what they usually eat. My impression is that it is usually necessary to remove most or all of the nutrition support calories before we can assess ability to take oral intake. Occasionally, we may need to restart nutrition support, at least temporarily, but then we know that we have given patients every opportunity to optimize oral intake, and perhaps avoid the placement of long-term enteral access. Obviously, patients must first be clear of absolute barriers to reasonable oral intake (such as severe nausea, mucositis, dysphagia, etc.), or have such barriers effectively treated/managed before you consider stopping nutrition support. Interrupting PN in these instances is also a good opportunity to re-assess the current plan. (“OK, they cannot meet their full needs, but clearly their GI tract is working, and no further indication for PN, so time to begin EN”).
There really should be no surprise that appetite is very different than nutrition needs. The obesity problem in many countries serves as a reminder than the desire for food can be very different than nutrition requirements. It is just that our malnourished patients who are sad, battling anorectic cytokines, and face-to-face with green jello or a pureed diet can ill afford to have their full nutrition needs met while we encourage them to eat.
It may be a surprise that seeking answers from the medical literature can be a bit like a teenager asking their parents for permission to stay out late. We have found that the answer you get may depend on who you ask and how you ask the question. The details for asking the right question, however, will have to wait for another time and another blog.
"Asking the right questions takes as much skill as giving the right answers." - Robert Half
1) Murray CD, le Roux CW, Gouveia C, et al. The effect of different macronutrient infusions on appetite, ghrelin and peptide YY in parenterally fed patients. Clin Nutr. 2006;25(4):626-633.
2) McCutcheon NB, Tennissen AM. Hunger and appetitive factors during total parenteral nutrition. Appetite. 1989:13(2):129-141
3) Jordan, H. A., Moses, H., MacFayden, B. V., Jr. & Dudrick, S. J. Hunger and satiety in humans during parenteral hyperalimentation. Psychosomatic Medicine. 1974; 36: 144-155.
4) Gil KM, Skeie B, Kvetan V, Askanazi J, Friedman MI. Parenteral nutrition and oral intake: effect of glucose and fat infusions. JPEN J Parenter Enteral Nutr. 1991 Jul-Aug;15(4):426-32.