Vidyya Medical News Service
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Volume 6 Issue 202 Published - 14:00 UTC 08:00 EST 20-Jul-2004 Next Update - 14:00 UTC 08:00 EST 21-Jul-2004
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A longer chain fatty acid, found in milk and beef products, is found to increase key peptide production and reduce appetite and energy intake

It appears that size matters when it comes to the length of the macromolecule found in fatty acids and the effect on appetite suppression. Researchers have determined that the longer the molecular chain, the more effective the fatty acid is in increasing important peptides associated with digestion. The reason is found in the actions of nutrients within the digestive system. 

Nutrients control appetite and energy intake through two principal mechanisms arising from the stomach and small intestine: (i) inhibition of gastric emptying, which activates stretch receptors, which detect the lengthening of a macromolecule; e.g., in the synthesis of long-chain fatty acids or in the synthesis of a protein; and (ii) triggering of neural and humoral signals as a result of the interaction of nutrients with the small intestine. While gastric and intestinal signals interact to modulate energy intake, studies in both humans and animals suggest that intestinal mechanisms are dominant.

The effects of fat on appetite, gastrointestinal motility and hormone release are dependent on digestion of triglycerides into free fatty acids. For example, in healthy subjects, inhibition of fat digestion by the lipase inhibitor, tetrahydrolipstatin, diminishes the effects of: (1) duodenal triglyceride on the perception of fullness, energy intake, antropyloroduodenal motor activity; (2) plasma cholecystokinin (CCK), a polypeptide hormone liberated by the upper intestinal mucosa on contact with gastric contents that stimulates contraction of the gallbladder and secretion of pancreatic juice, and (3) concentrations of glucagon-like peptide-1 (GLP-1), a gut hormone that slows gastric emptying and stimulates insulin secretion.

There is evidence that the gastrointestinal responses to fat are also dependent on the chain length of fatty acids within the intestinal tube. Fatty acids with Y12 carbon atoms are transported from the gut predominantly in lymphatic chylomicrons, a transport process that triggers a variety of gut signals including satiety and the slowing of gastric emptying.  Gastrointestinal peptides, including CCK and GLP-1, mediate, at least in part, the effects of fat on energy intake and gastrointestinal spontaneous movement, hence, the effects of fatty acid chain length on gastrointestinal hormone secretion are clearly of interest.

A New Study

A study in humans suggests that CCK is stimulated by infusion of lauric acid (a fatty acid also known as C12 (for 12 carbon atom length), occurring in spermaceti, in milk, and in laurel, coconut, and palm oils as well as waxes and marine fats) but not decanoic acid (a fatty acid called C10 (10 carbon atom length), obtained from animal fats and oils and used in the manufacture of perfumes and fruit flavors) within the first division of the small intestine. However, the control solution also raised plasma CCK concentrations, confounding interpretation of the data.  Researchers could not establish whether C10, if infused alone as a sodium salt, might release smaller, but detectable, amounts of CCK. There is no information as to how fatty acid chain length may affect the release of GLP-1.

The aims of this study were to evaluate in humans the hypotheses that: (i) intraduodenally administered C12 and C10 have different effects on appetite-related sensations and energy intake, (ii) C12, but not C10, releases CCK (44) and GLP-1 and (iii) effects on pressure patterns in the antrum, pylorus, and duodenum differ between C12 and C10.

The authors of “Effects of Intraduodenal Fatty Acids on Appetite, Antropyloroduodenal Motility and Plasma CCK and GLP-1 in Humans Vary with their Chain Length,” are Kate L. Feltrin, Tanya J. Little, James H. Meyer, Michael Horowitz, Judith Wishart, Amelia N. Pilichiewicz, Ian M. Chapman, and Christine Feinle-Bisset, all from the Department of Medicine, University of Adelaide, Royal Adelaide Hospital, Adelaide, South Australia, Australia; Andre JPM Smout at the Department of Gastroenterology, University Hospital, Utrecht, The Netherlands; and Thomas Rades with the School of Pharmacy, University of Otago, Dunedin, New Zealand.  Their findings are published in the Articles in Press of the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.

Methodology

Eight healthy males (19-47 years) were studied on three occasions in a double-blind, randomized fashion. Appetite perceptions, antropyloroduodenal pressure wave sequences and plasma CCK and GLP-1 concentrations were measured during a 90 min intraduodenal infusion of (i) C12, (ii) C10 or (iii) control (rate: 2 ml/min; 0.375 kcal/min for C12/C10). Energy intake at a buffet meal, immediately after completion of the infusion, was also quantified.

Results

The subjects, with the exception of one, tolerated all experimental conditions well. The subject, who was able to tolerate the C12 infusion for only 30 min due to severe nausea (and was dismissed at that time), completed the two other infusions successfully. All available data were included in the analyses.

The findings from this study has established that there are major differences in the effects of C12 and C10 fatty acids, when infused into the duodenum at a dose of 0.375 kcal/min, on appetite, antropyloroduodenal motility and gastrointestinal hormones in healthy males. When compared with an isocaloric dose of C10 and control, C12 reduced appetite and subsequent energy intake at a buffet meal, increased basal pyloric pressure, decreased antral and duodenal pressure waves, shortened the length of propagation of duodenal pressure waves, and increased plasma CCK and GLP-1 concentrations. While C10 stimulated CCK release, albeit less than C12, no effect on GLP-1 was evident.

Conclusions

While lauric acid is contained in a variety of foods, including coconut milk, butter, and beef, it, at least in most cases, does not represent a major component of the body’s total energy intake – on the basis of compositions of stored bodily fatty acids, it is estimated that C12 represents six percent of dietary fatty acids. Breast milk, which contains up to 20 percent of lauric acid, is only part of the human diet in early life.

In conclusion, our study demonstrated marked differences in the effects of isoenergetic doses of lauric (C12) and decanoic (C10) acid administered intraduodenally. C12, but not C10, inhibited appetite and energy intake; C12 modulated antropyloroduodenal motility patterns and increased plasma CCK and GLP-1 concentrations to a greater extent than the shorter-chained C10 fatty acid.

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Source:  Articles in Press of the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology. The journal is one of 14 published each month by the American Physiological Society (www.the-aps.org).



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