Table of Contents
In the last lesson we discussed protein and recommendations regarding quantity, quality, and other relevant aspects for overall health and dieting.
In this lesson we will do the same with dietary fat. Unlike with protein, there are no specific reasons why fat intake will be additionally beneficial for weight loss. However, fat intake is still important for general health purposes.(Liu, 2017)
Standard dietary guidelines suggest:
- 2-3 years old: 30-40% of one’s calories come from fat
- 4-18 years old: 25-35% of one’s calories come from fat
- 19+ years old: 20-35% of one’s calories come from fat
While protein discussed above has literature suggesting certain amounts per kilogram of body weight, there is no strong evidence base supporting fat be considered in the same manner.
Reasons for a minimum daily fat intake
The only two essential fatty acids are linoleic acid and linolenic acid, and one of the reasons for the lower range of calories listed above is to ensure that the recommended intakes for these are met:
- Linoleic acid (an omega-6 polyunsaturated fatty acid) is recommended at 7 grams/day age 1-3 and then 10-17 grams/day beyond that depending on age and gender
- Linolenic acid (an omega-3 polyunsaturated fatty acid) is recommended at 0.7 grams/day age 1-3 and then 0.9-1.6 grams/day beyond that depending on age and gender
Tip: As mentioned previously, you can plug a single day of eating into cronometer.com to see if you are meeting these essential fatty acid recommendations. However, as indicated in the prior note you can likely consume considerably less than the recommended intakes without significant risk of harm. Thus, I would not burden yourself too significantly to meet the recommended fat intake levels if it would otherwise prove troublesome to do so, especially when actively losing weight and thus consuming relatively few calories.
There are a handful of other reasons to consume dietary fat:
- Fat is additionally helpful for absorption of the four fat-soluble vitamins: A, D, E, and K.
- There is some evidence that fat intake below the above recommendations for extended periods can decrease testosterone levels, but it is unclear if this will impact skeletal muscle mass in a negative way.(Iraki, 2019)
- Lastly, some sources of fats are associated with beneficial health properties, (ie, nuts, olive oil, fatty fish). If daily fat intake was set too low these beneficial foods would have to be excluded.
Example: If a person wants to consume 2,000 kcal/day, 20% of this would be 400 kcal. Considering 9 kcal/gram of fat, this would equate to a minimum of 44 grams of fat daily, with ~1-2 grams being linolenic acid. 10+ grams of linoleic acid daily would likely be sufficient to meet health requirements in adults.
Reasons for a maximum daily fat intake
There is nothing inherently wrong with a high fat diet that goes beyond the upper limits of the ranges listed above; the upper limits were set with the thought that going higher will make it harder to get the other essential/healthy nutrients needed from sources of protein and carbohydrates (ie, several servings of fruits and vegetables) while still limiting total calories to an appropriate amount for body weight management. Thus, if total nutritional needs are being met and total caloric goal allows it, increasing fat intake above the previously mentioned upper limits is safe, though limits regarding saturated and trans fatty acids should be kept in mind (see below).
Note: Ketogenic diets are an example of a dietary strategy with fat intake considerably above the upper limit listed above. There are pros and cons of ketogenic diets; for example one pro is appetite suppression while one con is difficulty building skeletal muscle.(Gibson, 2015; Vargas, 2018) I will discuss ketogenic diets in more detail in Lesson 12.
Types of dietary fat
There are four chemical structures of fatty acids: saturated, monounsaturated, polyunsaturated, and trans.
Saturated fatty acids
The general health recommendation is to keep saturated fat intake at <10% of total calories. The American Heart Association recommends keeping saturated fat intake at <7% of total calories. There are several authors who disagree with this recommendation, and the overall literature base is riddled with controversy.(Liu, 2017; Harcombe, 2019; Kaur, 2020; Heileson, 2020) There is also evidence different saturated fatty acids have different health properties (example: saturated fat from dairy seems less harmful than saturated fat from meat).(Unger, 2019) A recent Cochrane review suggests a small benefit with reduction of saturated fat intake.(Hooper, 2020) For an overview of the full controversy, see the cited article series designed as an Oxford-style debate.(Kris-Etherton, 2020; Krauss, 2020a; Krauss, 2020b) At this point I agree with the notion of attempting to limit saturated fat intake to <10% of one’s daily calories, though going over this occasionally and especially with dairy is unlikely to pose any significant health risk. The one exception is when purposefully eating in a caloric surplus to gain weight where increasing saturated fat intake does seem more harmful.(Rosqvist, 2014)
As the saturated fat molecule is relatively linear, it is easy for them to stack on top of each other and thus they tend to be solids at room temperature.
Note: While the saturated fat from dairy seems less harmful than from other sources, a recent study replacing the saturated fat from dairy with unsaturated fat yielded improved health markers.(Vasilopoulou, 2020) Of note, large amounts of dairy were provided during this trial and it will need to be replicated with more realistic quantities.
Example: If a person wants to eat a 2,000 kcal/day diet, 10% of this is 200 kcal, and this would be generated from 200/9 = 22 grams of fat. Thus, they should aim to keep their saturated fat intake under 22 grams. If they have significant heart risks and want to keep with the American Heart Association guidelines, then they should keep their saturated fat intake under 2,000 * 0.07 / 9 = 16 grams daily.
Monounsaturated fatty acids
There are no specific recommendations for monounsaturated fat intake and the evidence overall is mixed regarding a benefit to purposely including more of this in the diet in lieu of other nutrients.(Fattore, 2018) Part of this confusion may stem from the source of the monounsaturated fatty acids as a recent study indicated a beneficial health impact when this is predominantly consumed from plant sources as opposed to animal sources.(Guasch-Ferré, 2019; Ros, 2019) Thus, it is possible monounsaturated fatty acids do not have significant health implications themselves but rather reflect the overall food matrix (see note below) within which they are present.
With both of the adjacent carbons of the double bond on the same side, this molecule is much less linear than saturated fat. These molecules thus stack together less well and will tend to form a liquid at room temperature.
Note: The term “food matrix” alludes to the full food source of the nutrients in question. Many studies are done on isolated nutrients but generally we do not consume nutrients in isolation. When we consume whole foods the health impact is not necessarily just the sum of the individual parts. This is due to potentially competing effects of nutrients within a food that can alter absorption but also to the many micronutrients and phytonutrients contained within a full food source that are generally not considered in studies of individual nutrients. This can lead to the differences seen in the plant vs animal sources of monounsaturated fatty acids and potentially the differences in saturated fatty acids from dairy vs nondairy sources (though the chemical structure of the saturated fatty acids may play a role here as well).
Polyunsaturated fatty acids
These are generally considered to have either positive or neutral effects on overall health. There is a body of evidence suggesting replacing saturated fatty acids with polyunsaturated fatty acids leads to better cardiovascular and overall health outcomes.(Siri-Tarino, 2015) However, not all research supports this, and controversy persists.(Fattore, 2018, Forouhi, 2018) Prior concerns of unhealthy ratios of omega 6 to omega 3 seem generally unfounded and may moreso reflect inadequate omega 3 intake rather than excessive omega 6 intake.(Maki, 2018; Marventano, 2015) The two essential fatty acids mentioned above, linoleic & linolenic acid, are both polyunsaturated. Overall there generally seems to be a potential benefit of increased polyunsaturated fatty acid intake without significant risk of harm.
Similar to monounsaturated fatty acids, polyunsaturated fatty acids do not stack well together and also tend to be liquids at room temperature.
Trans fatty acids
These are typically categorized as either industrial (a byproduct of baking or cooking certain products with high temperatures) or ruminant (produced by certain animals (ie, cows) and then absorbed with their consumption). The research almost universally indicates that industrial trans fatty acids are harmful to human health and should be avoided. The research on ruminant trans fatty acids is less clear with evidence generally suggesting they do not impart a harmful effect.(de Souza, 2015) One caveat here is that people typically have consumed ~2.5x more industrial than ruminant trans fat which would make it harder to pick up a harmful signal with the ruminant trans fatty acids. Overall I would not worry about consuming ruminant trans fatty acids while industrial trans fatty acids should be avoided.
Similar to saturated fatty acids, trans fatty acids have a mostly linear conformation, making them stack together more easily and more likely to be a solid fat at room temperature.
Dietary fat is important for a number of reasons, and the full range of positive and negative health impacts of the various types are not completely clear:
- Industrial trans fat is universally regarded as harmful
- Ruminant trans fat does not seem harmful in typically consumed quantities but may be harmful in larger quantities
- Saturated fat from processed meats and unprocessed red meats are generally considered harmful
- Saturated fat from dairy seems less harmful than from other sources
- Monounsaturated fat may be neutral towards health overall but beneficial and harmful when consumed from plant and animal sources, respectively
- Polyunsaturated fat is generally considered neutral or beneficial towards health
Similar to the last lesson where studies on isolated protein sources were not necessarily applicable to people eating food items and mixed meals, studies on isolated fatty acids are not necessarily applicable to whole food consumption. It is apparent with the significant controversy alluded to above that the sources of the fats play a large role in the overall health impact. For this reason much of the literature is starting to shift towards consideration of overall dietary patterns and food sources as opposed to just individual nutrients. Food groups are discussed in Lesson 10 and various diets are discussed in Lesson 12.
- de Souza RJ, Mente A, Maroleanu A, et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ. 2015;351:h3978. Published 2015 Aug 11. doi:10.1136/bmj.h3978
- Fattore E, Massa E. Dietary fats and cardiovascular health: a summary of the scientific evidence and current debate. Int J Food Sci Nutr. 2018;69(8):916‐927. doi:10.1080/09637486.2018.1455813
- Forouhi NG, Krauss RM, Taubes G, Willett W. Dietary fat and cardiometabolic health: evidence, controversies, and consensus for guidance. BMJ. 2018;361:k2139. Published 2018 Jun 13. doi:10.1136/bmj.k2139
- Gibson AA, Seimon RV, Lee CM, et al. Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obes Rev. 2015;16(1):64-76. doi:10.1111/obr.12230
- Guasch-Ferré M, Zong G, Willett WC, et al. Associations of Monounsaturated Fatty Acids From Plant and Animal Sources With Total and Cause-Specific Mortality in Two US Prospective Cohort Studies. Circ Res. 2019;124(8):1266‐1275. doi:10.1161/CIRCRESAHA.118.313996
- Harcombe Z. US dietary guidelines: is saturated fat a nutrient of concern?. Br J Sports Med. 2019;53(22):1393‐1396. doi:10.1136/bjsports-2018-099420
- Heileson JL. Dietary saturated fat and heart disease: a narrative review. Nutr Rev. 2020;78(6):474‐485. doi:10.1093/nutrit/nuz091
- Hooper L, Martin N, Jimoh OF, Kirk C, Foster E, Abdelhamid AS. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev. 2020;5:CD011737. Published 2020 May 19. doi:10.1002/14651858.CD011737.pub2
- Iraki J, Fitschen P, Espinar S, Helms E. Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review. Sports (Basel). 2019;7(7):154. Published 2019 Jun 26. doi:10.3390/sports7070154
- Kaur D, Tallman DA, Khosla P. The health effects of saturated fats – the role of whole foods and dietary patterns. Diabetes Metab Syndr. 2020;14(2):151‐153. doi:10.1016/j.dsx.2020.02.002
- Krauss RM, Kris-Etherton PM. Public health guidelines should recommend reducing saturated fat consumption as much as possible: NO [published online ahead of print, 2020a Jun 3]. Am J Clin Nutr. 2020a;nqaa111. doi:10.1093/ajcn/nqaa111
- Krauss RM, Kris-Etherton PM. Public health guidelines should recommend reducing saturated fat consumption as much as possible: Debate Consensus [published online ahead of print, 2020b Jun 3]. Am J Clin Nutr. 2020b;nqaa134. doi:10.1093/ajcn/nqaa134
- Kris-Etherton PM, Krauss RM. Public health guidelines should recommend reducing saturated fat consumption as much as possible: YES [published online ahead of print, 2020 Jun 3]. Am J Clin Nutr. 2020;nqaa110. doi:10.1093/ajcn/nqaa110
- Liu AG, Ford NA, Hu FB, Zelman KM, Mozaffarian D, Kris-Etherton PM. A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutr J. 2017;16(1):53. Published 2017 Aug 30. doi:10.1186/s12937-017-0271-4
- Maki KC, Eren F, Cassens ME, Dicklin MR, Davidson MH. ω-6 Polyunsaturated Fatty Acids and Cardiometabolic Health: Current Evidence, Controversies, and Research Gaps. Adv Nutr. 2018;9(6):688‐700. doi:10.1093/advances/nmy038
- Marventano S, Kolacz P, Castellano S, et al. A review of recent evidence in human studies of n-3 and n-6 PUFA intake on cardiovascular disease, cancer, and depressive disorders: does the ratio really matter?. Int J Food Sci Nutr. 2015;66(6):611‐622. doi:10.3109/09637486.2015.1077790
- Ros E. Contrasting Effects on Mortality of Monounsaturated Fatty Acid Intake Depending on Vegetable or Animal Sources. Circ Res. 2019;124(8):1154‐1156. doi:10.1161/CIRCRESAHA.119.314842
- Rosqvist F, Iggman D, Kullberg J, et al. Overfeeding polyunsaturated and saturated fat causes distinct effects on liver and visceral fat accumulation in humans. Diabetes. 2014;63(7):2356‐2368. doi:10.2337/db13-1622
- Siri-Tarino PW, Chiu S, Bergeron N, Krauss RM. Saturated Fats Versus Polyunsaturated Fats Versus Carbohydrates for Cardiovascular Disease Prevention and Treatment. Annu Rev Nutr. 2015;35:517‐543. doi:10.1146/annurev-nutr-071714-034449
- Unger AL, Torres-Gonzalez M, Kraft J. Dairy Fat Consumption and the Risk
of Metabolic Syndrome: An Examination of the Saturated Fatty Acids in
Dairy. Nutrients. 2019;11(9):2200. Published 2019 Sep 12. doi:10.3390/nu11092200
- Vargas S, Romance R, Petro JL, et al. Efficacy of ketogenic diet on body composition during resistance training in trained men: a randomized controlled trial. J Int Soc Sports Nutr. 2018;15(1):31. Published 2018 Jul 9. doi:10.1186/s12970-018-0236-9
- Vasilopoulou D, Markey O, Kliem KE, et al. Reformulation initiative for partial replacement of saturated with unsaturated fats in dairy foods attenuates the increase in LDL cholesterol and improves flow-mediated dilatation compared with conventional dairy: the randomized, controlled REplacement of SaturatEd fat in dairy on Total cholesterol (RESET) study. Am J Clin Nutr. 2020;111(4):739-748. doi:10.1093/ajcn/nqz344