The studies to date typically uses a ‘broad brush’ to paint fatty acids into classes based on their degree of saturation (i.e., saturated, or mono- or polyunsaturated) and not the food complex they are consumed in, nor the chain-length of the fats. This is in contrast to findings that different saturated fat types and different saturated fat-containing foods could have markedly different effects on health outcomes.
As previously noted, in the 2013 review by O’Sullivan et al.,1 no significant relationship was seen between dairy (the food group containing the highest amount of saturated fat) and either cardiovascular disease or all-cause mortality. While meat and processed meat were associated with an increase in all-cause mortality, meat was not associated with an increase in cardiovascular disease mortality. Notwithstanding that the discrepancy between meat and all-cause mortality and cardiovascular mortality the decrease in risk of mortality seen in Asians cast doubt upon the veracity of this finding, at the very least these results suggest that saturated fat is not a health risk per se but one’s food environment in totality is.
Chain-length of saturated fats is also likely to play a differentiating role in health outcomes. For example, the 4 carbon saturated fatty acid butyric acid is predominantly utilized by cells and bacteria of the colon and inhibits inflammation and carcinogenesis of the colonic mucosa along with decreasing oxidative stress and promoting of satiety.2, 3 Thus, it serves an important role in preserving the health of the colon, microbiota, and may have other beneficial roles for general and systemic health.
Medium-chain triglycerides (MCTs) made up predominantly of saturated fatty acids between 6 and 12 carbons in chain-length also offer benefits to health. MCTs increase ketone production allowing greater levels of a preferential fuel for cardiac tissue and providing an alternative fuel for the brain. This can protect against hypoglycaemia (low blood sugar),4 increase available adenosine (a relaxing neurotransmitter) and improved GABA-glutamate ratio, reducing over-excitation of neurons.5 Increased ketones also reduce inflammation,6 thereby reducing excitotoxicity (protecting neurons from this cytotoxic damage) and improve the structure and function of glial cells of the brain,7 and increase brain-derived neurotrophic factor.8
MCTs also show neuroprotective properties and there is evidence that they help to reduce the risk of Alzheimer’s and cognitive decline,9 and MCT supplemented diets improve cognition, mental performance and memory in those with Alzheimer’s Disease and other age-related cognitive declines.10-16
These brain and relaxant benefits also suggest a benefit to sleep from MCTs and this has been studied in new-borns consuming formula in which 37% of the fat content was from MCTs. The new-borns taking the MCT formula slept on average 52 mins longer than the LCT control.17
Diets rich in MCTs also promote greater fat-utilisation and weight/fat-loss than those containing an equivalent amount of (predominantly monounsaturated) olive oil or polyunsaturated-rich rapeseed/soybean oil.18, 19 They have been shown to have a particularly positive effect on fat in and around the midsection (internal and external ‘belly fat’) when compared to olive oil.20 MCTs also raise serum triglycerides (fats in the blood[i]), less than (commonly recommended) canola or soybean oils.21, 22 Additionally, several reports suggest that MCTs help preserve insulin sensitivity, both in animal models and patients with type 2 diabetes.23 In an over-feeding study in which calories were increased by 75% (from long-chain saturated fats), the substitution of 30 g of medium-chain fatty acids (for an equivalent amount of long-chain saturated fat) mitigated the reduction in insulin sensitivity and glucose disposal seen in the control group. The medium-chain fatty-acid supplementation increased fatty-acid oxidation, maintained glucose flexibility, increased glucose disposal, and increased glycogen synthase activity.24
Summary
So, it is clear that not all fats…and not all saturated fats are created equal and this has not been considered in the research to date. It is important to remember that short and medium-chain fatty acids are relatively sparse in the diet but are becoming more commonly used as supplements to the diet.
Read Part 1: What Do We Know from Observational Evidence?
Read Part 2: What Do We Know from Randomised Controlled Trials?
Read Part 3: What Effect Does Replacing Saturated Fat in the Diet Have on Heart Health?
Read Part 5: Summary of the Effects of Saturated Fat on Heart Health and Mortality
References
1. O’Sullivan TA, Hafekost K, Mitrou F, Lawrence D. Food Sources of Saturated Fat and the Association With Mortality: A Meta-Analysis. American Journal of Public Health. 2013;103(9):e31-e42.
2. Hamer HM, Jonkers D, Venema K, Vanhoutvin S, Troost FJ, Brummer RJ. Review article: the role of butyrate on colonic function. Aliment Pharmacol Ther 2008;27(2):104-19.
3. Fung KY, Cosgrove L, Lockett T, Head R, Topping DL. A review of the potential mechanisms for the lowering of colorectal oncogenesis by butyrate. Br J Nutr. 2012;108(05):820-31.
4. Schutz PW. Neuroprotective effects of ketone bodies during hypoglycemia: University of British Columbia; 2011.
5. Hertz L, Chen Y, Waagepetersen HS. Effects of ketone bodies in Alzheimer’s disease in relation to neural hypometabolism, β-amyloid toxicity, and astrocyte function. Journal Of Neurochemistry. 2015;134(1):7-20.
6. Youm Y-H, Nguyen KY, Grant RW, Goldberg EL, Bodogai M, Kim D, et al. The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease. Nat Med. 2015;21(3):263-9.
7. Gzielo K, Soltys Z, Rajfur Z, Setkowicz ZK. The Impact of the Ketogenic Diet on Glial Cells Morphology. A Quantitative Morphological Analysis. Neuroscience. 2019.
8. Kim SW, Marosi K, Mattson M. Ketone beta-hydroxybutyrate up-regulates BDNF expression through NF-κB as an adaptive response against ROS, which may improve neuronal bioenergetics and enhance neuroprotection (P3.090). Neurology. 2017;88(16 Supplement).
9. Chatterjee P, Fernando M, Fernando B, Dias CB, Shah T, Silva R, et al. Potential of coconut oil and medium chain triglycerides in the prevention and treatment of Alzheimer’s disease. Mechanisms of Ageing and Development. 2020;186:111209.
10. Reger MA, Henderson ST, Hale C, Cholerton B, Baker LD, Watson GS, et al. Effects of β-hydroxybutyrate on cognition in memory-impaired adults. Neurobiology of Aging. 2004;25(3):311-4.
11. Cunnane SC, Courchesne-Loyer A, St-Pierre V, Vandenberghe C, Pierotti T, Fortier M, et al. Can ketones compensate for deteriorating brain glucose uptake during aging? Implications for the risk and treatment of Alzheimer’s disease. Annals of the New York Academy of Sciences. 2016;1367(1):12-20.
12. Kimoto A, Ohnuma T, Toda A, Takebayashi Y, Higashiyama R, Tagata Y, et al. Medium-chain triglycerides given in the early stage of mild-to-moderate Alzheimer’s disease enhance memory function. Psychogeriatrics : the official journal of the Japanese Psychogeriatric Society. 2017;17(6):520-1.
13. Xu Q, Zhang Y, Zhang X, Liu L, Zhou B, Mo R, et al. Medium-chain triglycerides improved cognition and lipid metabolomics in mild to moderate Alzheimer’s disease patients with APOE4−/−: A double-blind, randomized, placebo-controlled crossover trial. Clinical Nutrition. 2019.
14. Abe S, Ezaki O, Suzuki M. Medium-Chain Triglycerides in Combination with Leucine and Vitamin D Benefit Cognition in Frail Elderly Adults: A Randomized Controlled Trial. Journal of Nutritional Science and Vitaminology. 2017;63(2):133-40.
15. Fortier M, Castellano C-A, St-Pierre V, Myette-Côté É, Langlois F, Roy M, et al. A ketogenic drink improves cognition in mild cognitive impairment: Results of a 6-month RCT. Alzheimer’s & Dementia.n/a(n/a).
16. Avgerinos KI, Egan JM, Mattson MP, Kapogiannis D. Medium Chain Triglycerides induce mild ketosis and may improve cognition in Alzheimer’s disease. A systematic review and meta-analysis of human studies. Ageing Research Reviews. 2020;58:101001.
17. Telliez F, Bach V, Leke A, Chardon K, Libert J-P. Feeding behavior in neonates whose diet contained medium-chain triacylglycerols: short-term effects on thermoregulation and sleep. The American Journal of Clinical Nutrition. 2002;76(5):1091-5.
18. St-Onge M-P, Ross R, Parsons WD, Jones PJH. Medium-Chain Triglycerides Increase Energy Expenditure and Decrease Adiposity in Overweight Men. Obesity Research. 2003;11(3):395-402.
19. Tsuji H, Kasai M, Takeuchi H, Nakamura M, Okazaki M, Kondo K. Dietary Medium-Chain Triacylglycerols Suppress Accumulation of Body Fat in a Double-Blind, Controlled Trial in Healthy Men and Women. The Journal of Nutrition. 2001;131(11):2853-9.
20. St-Onge M-P, Bosarge A. Weight-loss diet that includes consumption of medium-chain triacylglycerol oil leads to a greater rate of weight and fat mass loss than does olive oil. The American Journal of Clinical Nutrition. 2008;87(3):621-6.
21. Calabrese C, Myer S, Munson S, Turet P, Birdsall TC. A cross-over study of the effect of a single oral feeding of medium chain triglyceride oil vs. canola oil on post-ingestion plasma triglyceride levels in healthy men. Altern Med Rev. 1999;4(1):23-8.
22. Kasai M, Maki H, Nosaka N, Aoyama T, Ooyama K, Uto H, et al. Effect of Medium-chain Triglycerides on the Postprandial Triglyceride Concentration in Healthy Men. Bioscience, Biotechnology, and Biochemistry. 2003;67(1):46-53.
23. Nagao K, Yanagita T. Medium-chain fatty acids: Functional lipids for the prevention and treatment of the metabolic syndrome. Pharmacological Research. 2010;61(3):208-12.
24. Lundsgaard A-M, Fritzen AM, Sjøberg KA, Kleinert M, Richter EA, Kiens B. Small Amounts of Dietary Medium-Chain Fatty Acids Protect Against Insulin Resistance During Caloric Excess in Humans. Diabetes. 2021;70(1):91-8.
[i] High triglycerides are a key indicator heart disease and stroke risk and are one of the first markers that clinicians look to reduce.
