Lauric Acid-Rich Medium-Chain Triglycerides Can Substitute for Other Oils in Cooking Applications and May Have Limited Pathogenicity

Lauric Acid-Rich Medium-Chain Triglycerides Can Substitute for Other Oils in Cooking Applications and May Have Limited Pathogenicity

Cardiac risk factors and prevention Open Heart: first published as 10.1136/openhrt-2016-000467 on 27 July 2016. Downloaded from Lauric acid-rich medium-chain triglycerides can substitute for other oils in cooking applications and may have limited pathogenicity Mark F McCarty, James J DiNicolantonio To cite: McCarty MF, ABSTRACT antibacterial pharmaceuticals (eg, mono- DiNicolantonio JJ. Lauric Recently, medium-chain triglycerides (MCTs) laurin) and other worthwhile compounds. acid-rich medium-chain containing a large fraction of lauric acid (LA) (C12)— triglycerides can substitute Coconut oil is one of the richest available about 30%—have been introduced commercially for — for other oils in cooking sources of LA constituting about half of its use in salad oils and in cooking applications. As applications and may have total fatty acid content—and so is used to compared to the long-chain fatty acids found in other limited pathogenicity. Open produce LA; the shorter chain fats are hence Heart cooking oils, the medium-chain fats in MCTs are far 2016;3:e000467. by-products of this process and then are used doi:10.1136/openhrt-2016- less likely to be stored in adipose tissue, do not give 000467 rise to ‘ectopic fat’ metabolites that promote insulin for production of MCTs. As contrasted with resistance and inflammation, and may be less likely to coconut oil, standard MCTs are consistently activate macrophages. When ingested, medium-chain fluid at room temperature; their utility for Received 3 May 2016 fatty acids are rapidly oxidised in hepatic mitochondria; cooking applications, however, is limited by Revised 9 June 2016 the resulting glut of acetyl-coenzyme A drives ketone their low smoke point, which makes them Accepted 2 July 2016 body production and also provokes a thermogenic unsuitable for use in frying. response. Hence, studies in animals and humans Recently, however, manufacturers have indicate that MCT ingestion is less obesogenic than started to produce a novel type of MCT that comparable intakes of longer chain oils. Although LA contains a high fraction of LA—typically tends to raise serum cholesterol, it has a more — 30%. A tablespoon of this MCT containing http://openheart.bmj.com/ substantial impact on high density lipoprotein (HDL) — than low density lipoprotein (LDL) in this regard, such 14 g of fat is said to contain 12 g of that the ratio of total cholesterol to HDL cholesterol medium-chain fatty acids (lauric 4.45 g, cap- decreases. LA constitutes about 50% of the fatty acid rylic 3.35 g, capric 4.00 g) and 1 g of unsatu- content of coconut oil; south Asian and Oceanic rates (presumably largely oleic acid). Hence, societies which use coconut oil as their primary source the content of longer chain saturated fatty of dietary fat tend to be at low cardiovascular risk. acids is extremely low and of questionable Since ketone bodies can exert neuroprotective effects, physiological significance. the moderate ketosis induced by regular MCT ingestion may have neuroprotective potential. As compared to on September 29, 2021 by guest. Protected copyright. traditional MCTs featuring C6–C10, laurate-rich MCTs are more feasible for use in moderate-temperature METABOLIC FATES OF MEDIUM-CHAIN frying and tend to produce a lower but more sustained TRIGLYCERIDES pattern of blood ketone elevation owing to the more The fatty acids featured in MCTs are charac- gradual hepatic oxidation of ingested laurate. terised by a limited potential for storage as triglycerides. This reflects the fact that they cannot be employed for de novo synthesis of diacylglycerol or phosphatidic acid.12 TRIGLYCERIDES SYNTHESISED FROM However, they can act as substrates, to a COCONUT OIL limited extent, for diacylglycerol acyltransfer- Standard medium-chain triglycerides (MCTs) ase; laurate is more active in this regard than are produced by hydrolysing coconut oil and the shorter chain fatty acids.12This means esterifying the fatty acids shorter than lauric that medium-chain fatty acids can participate Catalytic Longevity, Encinitas, acid (LA) (C12) with glycerol; the resulting in triglyceride synthesis when other longer California, USA triglycerides are rich primarily in caprylic chain fatty acids are present to generate Correspondence to (C8) and capric (C10) acids. The exclusion diacylglycerol. Dr Mark F McCarty; of LA reflects the fact that this fatty acid has The half life of ingested medium-chain [email protected] high commercial value as a precursor for fatty acids (MCFAs) tends to be short not McCarty MF, DiNicolantonio JJ. Open Heart 2016;3:e000467. doi:10.1136/openhrt-2016-000467 1 Open Heart Open Heart: first published as 10.1136/openhrt-2016-000467 on 27 July 2016. Downloaded from only because the capacity for their storage is less than via direct storage in adipocytes.10 Moreover, bolus inges- that for longer chain fats but also because they can tion of MCTs tends to trigger thermogenesis, presum- enter mitochondria efficiently without preliminary ably reflecting the fact that a glut of acetyl-coenzyme A esterification to carnitine.3 Conversion of fatty acyl- production in mitochondria tends to trigger protective – coenzyme As to fatty acyl-carnitines in the cytoplasm uncoupling mechanisms.11 13 Studies in rodents and (via carnitine palmitoyltransferase-I—CPT-I) is a humans indicate that, when diets are fed containing process tightly regulated in regard to metabolic need. comparable amounts of MCTs or longer chain fats, the When cellular glucose availability is ample, CPT-I is MCT diets are less obesogenic.14 Hence, it has been pro- inhibited by malonyl-coenzyme A; insulin activity also posed that MCTs should be used as an oil source by inhibits this enzyme.4 Ketosis only develops when the people who are attempting to control their weights.13 liver is glycogen depleted and insulin levels are low, such The adverse impact of excessive fatty acid exposure on that CPT-I activity is disinhibited.5 Under these circum- health—especially long-chain saturated fatty acids—is stances, fatty acids in the portal circulation have rapid attributable not only to modulation of serum lipid profile, access to the inner matrix of mitochondria in hepato- or promotion of obesity but also to the production of cytes; their subsequent oxidative degradation gives rise ‘ectopic fat’ metabolites within tissues that interfere with – to a glut of acetyl-coenzyme A, some of which will be insulin signalling and promote inflammation.15 19 converted to ketone bodies that enter the circulation. A Ceramide and diacylglycerol appear to be prominent in bolus dose of MCTs likewise can give rise to ketone pro- this regard. The production of these metabolites tends to duction in hepatocytes—even in the context of ample be greater in obese people with an insulin-resistant fat glycogen availability—because medium-chain fatty acids depot, especially when they consume diets rich in fat and can stream into hepatic mitochondria efficiently, where carbohydrates; indeed, these metabolites are suspected to they are rapidly converted either to ketone bodies or to mediate many of the adverse effects of metabolic syn- 3 20–23 CO2. (Insulin/glucagon balance, however, can still par- drome. It is notable that MCFAs are incapable of tially regulate ketone production as it can influence the giving rise to such metabolites.12A number of studies in activity and expression of the rate-limiting enzyme for rats or humans have found that, as contrasted with long- ketone body production, HMG-coenzyme A synthetase;6 chain fatty acids, diets featuring MCFAs are less likely to – hence, a somewhat higher proportion of medium-chain induce insulin resistance24 27—albeit a few studies con- fatty acids may be converted to ketone bodies during clude otherwise.28 fasting metabolism). Longer chain saturated fatty acids have the ability to The high ketogenicity of C8 and C10 further reflects upregulate activation of macrophages/microglia via pro- the fact that, as they are poorly incorporated into chylo- motion of toll-like receptor signalling and by supporting – microns but are relatively soluble, they tend to enter the ceramide synthesis.29 32 Conceivably, this helps to ration- http://openheart.bmj.com/ portal circulation directly after absorption (as opposed alise the many epidemiological studies associating meta- to the lymphatics) and hence have rapid access to the bolic syndrome and long-chain saturate-rich diets with liver. Rodent studies show that LA has a higher propen- increased risk for neurodegenerative disorders and sity to be absorbed via the lymphatics (presumably atherogenesis.33 34 Although MCFAs cannot give rise to reflecting its greater capacity for incorporation into tri- palmitate and have not promoted macrophage activation glycerides), and so its access to the liver is delayed.78 in some studies, other researchers report that, especially Logically, this delay should imply that the rise of ketone under low-serum conditions, LA can activate macro- bodies after laurate ingestion is delayed and that a some- phages by promoting signalling via certain toll-like on September 29, 2021 by guest. Protected copyright. what lower proportion of this fatty acid (as compared to receptors—TLR2 heterodimers and TLR4 homodi- C8 or C10) is ultimately converted to ketones; the latter mers.29 35 Also, macrophages can express a receptor for can be deduced from the fact that a sudden glut of MCFAs, GPR84, which can exert a pro-inflammatory hepatic mitochondrial acetyl-coenzyme A is more pro- effect.36 Whether these in vitro

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