Diagnosis of fat malabsorption by breath tests: just a breeze?

studies published in English that directly investigate absorption of various nutrients in patients following gastric resections [3–7] . Accordingly, the current study performed by Nakamura et al. [1] makes a significant contribution to our understanding of pathophysiological consequences of different surgical procedures for reconstruction after gastrectomy and may help to guide the choice of surgical techniques. Another interesting aspect of this study is that the authors employ a modern technique for their measurements, that is a breath test using 13 C-labeled lipids. This test may have diagnostic importance beyond the specific aims of this study: 13 C-marked triglycerides are nonradioactive and can be applied safely and repeatedly, also to children and pregnant women. Breath tests using these lipids are based on the principle that intestinal triglyceride absorption requires prior hydrolysis by lipase to produce free fatty acids and monoacylglycerol. These metabolites are incorporated into micelles, absorbed, resynthesized and transported to the liver. Lipolytic hepatic enzymes subsequently release 13 C-marked fatty acids. These undergo  -oxidation which results in formation of 13 CO 2 that is absorbed into the bloodstream, transported to the lung and exhaled. The increase in 13 CO 2 concentration in breath thus correlates with intestinal lipid digestion and absorption. Accordingly, breath tests based on 13 C-labeled lipids can be used as a substitute for the unpopular direct measurement of fecal fat excretion as done by Nakamura et al. [1] in their recent study and as several other investigators did earlier [3, 8, 9] . Lipid-based 13 C-breath tests have not only been used successfully for In this issue of Digestion Nakamura et al. [1] report differential fat digestion and absorption rates in patients after subtotal gastrectomy who underwent different surgical procedures for reconstruction, that is Billroth I or Roux-en-Y. Using a noninvasive breath test they show that the Billroth I procedure allows almost normal triglyceride digestion and absorption. By contrast, the Roux-en-Y procedure is associated with a 30–40% decrease in fat absorption compared with both healthy controls and patients who have undergone the Billroth I procedure. These findings are not entirely new but rather confirm the accepted opinion that maintenance of food passage through the duodenum is of importance for efficacy of nutrient digestion and absorption in patients who have undergone subtotal gastrectomy, and that therefore the Billroth I procedure is the more physiological approach. Moreover, patient allocation to the two treatment groups appears questionable and the numbers of subjects per group are not too impressive: either Billroth I (n = 17) or Roux-en-Y (n = 14) was performed according to the surgeons’ preferences in 31 patients overall and data obtained in these patients were compared with fat absorption rates of 15 healthy volunteers. By contrast, Ogoshi et al. [2] examined data of more than 1,000 patients who underwent total or partial gastrectomies because of gastric cancer. They showed that duodenal food passage reconstruction was an independent prognostic factor for improved survival rate. However, retrospective studies like this do, of course, not allow a comparison of the absorption of specific nutrients. Overall, there is an astonishing paucity of experimental Published online: June 26, 2009