Total Fat Consumption on Health
and Fatty Acid Metabolism

Total dietary fat intake has a significant effect on fatty acid metabolism and is an important factor in determination of how much of which fatty acids should be consumed. For example, in human experiments low-fat diet was found to increase tissue levels of omega-3. Non-essential fatty acids can interfere with the activity of essential fatty acids.

Multiple factors have to be considered in preparing an optimal fat formulation. For example, it was a widely held assumption that Monounsaturated Fatty Acids (MUFA – such as in olive oils) are heart healthy. But this belief may be too simplistic. Several interesting conclusions that challenge existing beliefs about MUFA came from a symposium on Fatty Acids held by the National Lipid Association in 2011 and are listed below:

  • Replacing dietary Saturated Fatty Acids (SFA) with PUFA has been shown to lower incidence of Coronary Heart Disease. However, when replacing SFA with MUFA, a similar benefit is not always seen.
  • Research indicates that dietary PUFA may be more cardio-protective than MUFA. The Mediterranean diet receives accolades for being a heart healthy diet and it was assumed for a long time that it is because of the significant amount of olive oil (MUFA) used. However, the benefits of MUFA are now in question and the Mediterranean diet may be cardio-protective because of the many other factors besides olive oil. Relying upon olive oil as the main source of dietary fat may actually be detrimental.
  • Although MUFA have been shown to improve high-density cholesterol levels, which has been suggested to be good cholesterol, this may not translate to lower risk of cardiac events. In experiments, MUFA was found to be associated with atherosclerosis.

Review this National Lipid Association publication for more information:

Fatty acids in cardiovascular health and disease: a comprehensive update

Baum SJ, Kris-Etherton PM, Willett WC, Lichtenstein AH, Rudel LL, Maki KC, Whelan J, Ramsden CE, Block RC. J Clin Lipidol. 2012 May-Jun;6(3):216-34. doi: 10.1016/j.jacl.2012.04.077. Epub 2012 Apr 13

Research dating back to the 1950s reported an association between the consumption of saturated fatty acids (SFAs) and risk of coronary heart disease. Recent epidemiological evidence, however, challenges these findings. It is well accepted that the consumption of SFAs increases low-density lipoprotein cholesterol (LDL-C), whereas carbohydrates, monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) do not. High-density lipoprotein (HDL)-C increases with SFA intake. Among individuals who are insulin resistant, a low-fat, high-carbohydrate diet typically has an adverse effect on lipid profiles (in addition to decreasing HDL-C, it also increases triglyceride and LDL particle concentrations). Consequently, a moderate fat diet in which unsaturated fatty acids replace SFAs and carbohydrates are not augmented is advised to lower LDL-C; compared with a low-fat diet, a moderate-fat diet will lower triglycerides and increase HDL-C. Now, there is some new evidence that is questioning the health benefits of even MUFAs and PUFAs. In addition, in a few recent studies investigators have also failed to demonstrate expected cardiovascular benefits of marine-derived omega-3 fatty acids. To clarify the clinical pros and cons of dietary fats, the National Lipid Association held a fatty acid symposium at the 2011 National Lipid Association Scientific Sessions. During these sessions, the science regarding the effects of different fatty acid classes on coronary heart disease risk was reviewed.

Fatty acid composition of skeletal muscle reflects dietary fat composition in humans

Andersson A, Nälsén C, Tengblad S, Vessby B.,Am J Clin Nutr. 2002 Dec;76(6):1222-9

BACKGROUND: It is still unknown whether the fatty acid composition of human skeletal muscle lipids is directly influenced by the fat composition of the diet. OBJECTIVE: We investigated whether the fatty acid composition of the diet is reflected in the fatty acid profile of skeletal muscle phospholipids and triacylglycerols. DESIGN: Thirty-two healthy adults (25 men and 7 women) included in a larger controlled, multicenter dietary study were randomly assigned to diets containing a high proportion of either saturated fatty acids (SFAs) [total fat, 36% of energy; SFAs, 18% of energy; monounsaturated fatty acids (MUFAs), 10% of energy] or MUFAs (total fat, 35% of energy; SFAs, 9% of energy; MUFAs, 19% of energy) for 3 mo. Within each diet group, there was a second random assignment to supplementation with fish oil capsules [containing 3.6 g n-3 fatty acids/d; 2.4 g eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)] or placebo. A muscle biopsy sample was taken from the vastus lateralis muscle after the diet period. Parallel analyses of diet and supplementation effects were performed. RESULTS: The proportions of myristic (14:0), pentadecanoic (15:0), heptadecanoic (17:0), and palmitoleic (16:1n-7) acids in the skeletal muscle phospholipids were higher and the proportion of oleic acid (18:1n-9) was lower in the SFA group than in the MUFA group. The proportion of total n-3 fatty acids in the muscle phospholipids was approximately 2.5 times higher, with a 5 times higher proportion of eicosapentaenoic acid (20:5n-3), in subjects supplemented with n-3 fatty acids than in those given placebo. Similar differences were observed in the skeletal muscle triacylglycerols. CONCLUSION: The fatty acid composition of skeletal muscle lipids reflects the fatty acid composition of the diet in healthy men and women.

Dietary fats and membrane function: implications for metabolism and disease

Hulbert AJ, Turner N, Storlien LH, Else PL., Biol Rev Camb Philos Soc. 2005 Feb;80(1):155-69

Lipids play varied and critical roles in metabolism, with function dramatically modulated by the individual fatty acid moities in complex lipid entities. In particular, the fatty acid composition of membrane lipids greatly influences membrane function. Here we consider the role of dietary fatty acid profile on membrane composition and, in turn, its impact on prevalent disease clusters of the metabolic syndrome and mental illness. Applying the classical physiological conformer-regulator paradigm to quantify the influence of dietary fats on membrane lipid composition (i.e. where the membrane variable is plotted against the same variable in the environment–in this case dietary fats), membrane lipid composition appears as a predominantly regulated parameter. Membranes remain relatively constant in their saturated (SFA) and monounsaturated (MUFA) fatty acid levels over a wide range of dietary variation for these fatty acids. Membrane composition was found to be more responsive to n-6 and n-3 polyunsaturated fatty acid (PUFA) levels in the diet and most sensitive to n-3 PUFA and to the n-3/n-6 ratio. These differential responses are probably due to the fact that both n-6 and n-3 PUFA classes cannot be synthesised de novo by higher animals. Diet-induced modifications in membrane lipid composition are associated with changes in the rates of membrane-linked cellular processes that are major contributors to energy metabolism. For example, in the intrinsic activity of fundamental processes such as the Na+/K+ pump and proton pump-leak cycle. Equally, dietary lipid profile impacts substantially on diseases of the metabolic syndrome with evidence accruing for changes in metabolic rate and neuropeptide regulation (thus influencing both sides of the energy balance equation), in second messenger generation and in gene expression influencing a range of glucose and lipid handling pathways. Finally, there is a growing literature relating changes in dietary fatty acid profile to many aspects of mental health. The understanding of dietary lipid profile and its influence on membrane function in relation to metabolic dysregulation has exciting potential for the prevention and treatment of a range of prevalent disease states.

Total Fat Intake Modifies Plasma Fatty Acid Composition in Humans

Susan K. Raatz,*2 Douglas Bibus,† William Thomas** and Penny Kris-Etherton‡*General Clinical Research Center, †Hormel Institute and **Division of Biostatistics,School of Public Health, University of Minnesota, Minneapolis, Minnesota 55455 and‡Nutrition Department, Pennsylvania State University, University Park, Pennsylvania16802 J. Nutr. 131: 231–234, 2001

Plasma fatty acid composition reflects dietary fatty acids. Whether the total fat content of the diet alters the fatty acid composition of plasma phospholipid, cholesteryl ester, triacylglycerol and free fatty acids is unknown. To evaluate the effects of low versus high fat diets on plasma fatty acids, a 12-wk, randomized, crossover, controlled feeding trial was conducted in healthy men and women with isoenergic low fat (20% energy) and high fat (45% energy) diets containing constant proportions of fatty acids. Ten subjects consumed one experimental diet for 28 d, their usual diet for 4 wk and the alternate experimental diet for 28 d. Endpoint measures of plasma fatty acids were determined at the end of each experimental period. The effects of the two diets were compared within subjects by analysis of variance. Plasma fatty acids (%) varied in response to total dietary fat with significantly greater total polyunsaturated fat, (n-6) and 18:2(n-6) levels in phospholipids and cholesteryl esters after high fat dietary consumption. The low fat diet was associated with significantly greater total (n-3) fatty acids, 20:5(n-3) and 22:6(n-3) levels in plasma phospholipid fatty acids and cholesteryl esters. Consumption of a low fat diet alters fatty acid patterns in a manner similar to that observed with feeding of (n-3) long-chain fatty acids. This change is likely related to decreased competition for the enzymes of elongation and desaturation, with reduced total intake of 18:2 (n-6) favoring elongation and desaturation of available (n-3) fatty acids.

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