Jeppesen P B, Mortensen P B
Department of Medicine, Rigshospitalet, University of Copenhagen, Denmark.
JPEN J Parenter Enteral Nutr. 1999 Sep-Oct;23(5 Suppl):S101-5. doi: 10.1177/014860719902300525.
Gut function and the degree of intestinal insufficiency or failure in short bowel patients can be quantified with respect to wet weight and energy absorption by the use of balance studies. This enables the physician to distinguish patients with extreme intestinal failure inconsistent with the restoration of intestinal autonomy by dietary manipulation from short bowel patients with borderline gut failure in whom dietary manipulations may result in the weaning from parenteral support. A high-carbohydrate, low long-chain fat diet and a diet where long-chain fat has been replaced by medium-chain triglycerides increase absorption of energy in patients with small bowel failure, provided that they have a preserved colon in continuity. This is due to the ability of the colonic flora to ferment carbohydrates malabsorbed in the small bowel to the short-chain fatty acids (SCFAs). These SCFAs are easily absorbed across the colonic mucosa resulting in a salvage of carbohydrate energy that otherwise would have been lost in feces. In contrast, long-chain fatty acids are not absorbed by the colon, and long-chain fat malabsorbed in the small bowel of short bowel patients are not retained in the large bowel. Recent work has indicated that the water soluble medium-chain fatty acids are effectively absorbed in the large bowel similar to the SCFAs. This may explain an almost complete absorption of medium-chain triglycerides in short bowel patients, even in patients with virtually no absorption of long-chain fat, and why this only occurs in patients with a colon in continuity. Manipulation of the dietary fat:carbohydrate ratio is much less efficacious in short bowel patients with no colonic function, and the use of medium-chain triglycerides has no proven effect on overall energy absorption from short bowel patients without a large bowel in continuity. Hence, the colon has increasingly important digestive functions as small bowel failure proceeds, not only when it comes to absorption of water and sodium, but also of energy from carbohydrates and medium-chain fat.
通过平衡研究，可以根据湿重和能量吸收对短肠患者的肠道功能以及肠道功能不全或衰竭的程度进行量化。这使医生能够区分出肠道功能极度衰竭、无法通过饮食调整恢复肠道自主功能的患者，与肠道功能处于临界衰竭状态、饮食调整可能使其摆脱肠外营养支持的短肠患者。对于小肠衰竭患者，高碳水化合物、低长链脂肪饮食以及用中链甘油三酯替代长链脂肪的饮食，可增加能量吸收，前提是他们有连续的保留结肠。这是因为结肠菌群能够将小肠中吸收不良的碳水化合物发酵成短链脂肪酸（SCFAs）。这些短链脂肪酸很容易通过结肠黏膜吸收，从而挽救了原本会随粪便流失的碳水化合物能量。相比之下，长链脂肪酸不会被结肠吸收，短肠患者小肠中吸收不良的长链脂肪也不会保留在大肠中。最近的研究表明，水溶性中链脂肪酸在大肠中能像短链脂肪酸一样被有效吸收。这或许可以解释为什么短肠患者即使几乎完全无法吸收长链脂肪，中链甘油三酯仍能几乎完全被吸收，以及为什么这种情况只发生在有连续结肠的患者身上。对于没有结肠功能的短肠患者，调整饮食中脂肪与碳水化合物的比例效果要差得多，而且使用中链甘油三酯对没有连续大肠的短肠患者的总体能量吸收没有经证实的效果。因此，随着小肠衰竭的进展，结肠的消化功能变得越来越重要，不仅在水和钠的吸收方面，而且在碳水化合物和中链脂肪能量的吸收方面。
