Lipids are stored in specialized cells, called adipocytes, in the form of triglycerides (esters of a glycerol molecule bonded to three fatty acids). (1) Groups of adipocytes compose adipose tissue, which is a loose type connective tissue. Adipocytes can swell and shrink depending on whether the triglycerides are being stored or burned as fuel. White adipose tissue stores energy and insulates, while brown and beige fat are permeated with capillaries and mitochondria and responsible for burning energy and generating heat. (2)
Fats in the subcutaneous layer of skin provide insulation to help our thermoregulation and maintain homeostasis, and act as cushioning to help protect our bones and organs from damage in the event of physical insults. Fats and oils also compose the structure of our integumentary system (hair, skin, nails), and maintain elastic membranes covering our organs. The blood-brain barrier is composed of CNS (central nervous system) endothelial cells with a unique lipid composition. (3)
If you weren’t convinced before that fat is vital for life, I hope this brings it home.
Eating fats in proportion and conjunction with other foods is not only beneficial, it’s vital for proper absorption of essential nutrients, such as fat-soluble vitamins (A, D, E, K). In addition, both fats and proteins slow down the rapid breakdown of carbohydrates into simple sugars, thus helping to regulate spikes in blood glucose levels.
Finally, fats and oils are delicious! They are calorie-dense, so just small amounts of them go a long way. They add flavor and taste, and therefore satisfaction, to meals. Adding a little bit of lipids to your plate will help increase fat-soluble nutrient absorption, regulate blood glucose/insulin spikes, and add a feeling of fullness and satiety to the consumer.
Cholesterol is a type of sterol (steroid-like lipid molecule), that is biosynthesized in all animal cells. Cholesterol is essential to the structure, permeability and fluidity of each cell’s phospholipid bilayer membrane. (4) It plays a huge role in protecting neurons (comprising the myelin sheath covering) and enabling efficient nerve conduction. (5) Some of our chemical messengers (both intracellular and between cells) are synthesized from cholesterol backbones that undergo various metabolic and catabolic changes. Examples of this are bile salts (to help digest fats and absorb fat-soluble vitamins), steroidal hormones (mineralocorticoids, glucocorticoids, androgens, estrogens, progestogens) and vitamin D (which has many roles, including maintenance of calcium and phosphorus blood levels, and helping to support immune function). (6)
There are a lot of misconceptions about dietary cholesterol recommendations. Because we can synthesize cholesterol, albeit with a complex 37-step process, we don’t technically need to obtain it from food. (7) On the other hand, the bad rep of excess cholesterol consumption leading to heart disease doesn’t really hold a candle to the actual mechanism. Let me explain: an overabundance of cholesterol is definitely implicated in plaque formation in arteries, thus increasing chances of heart attack and stroke. The controversy is whether the excess cholesterol comes from the diet or not. The key players in cholesterol balance are the carrier proteins that either carry the cholesterol molecules towards the heart (LDL, low density lipoproteins), or away from the heart to be eliminated via the hepatic pathway in the bile (HDL, high density lipoproteins). The ratio of LDL to HDL will determine whether the balance is in favor of deposits around the heart or not; additionally there are VLDL (very low density lipoprotein) carriers that indicate even more potential for harm. It also matters whether the cholesterol particles are “fluffy/light” or “sticky/heavy.” However, these factors are independent of our diet. Dietary cholesterol is usually processed and absorbed, and compensated for in the body by automatically lowering synthesis in our own cells. Most people who have issues with cholesterol overabundance are not excessive in their diet, but have genetic predisposition for an unfavorable lipoprotein picture and therefore a higher probability of plaque formations and subsequent health risks.
Plants can be sources of cholesterol analogs, called phytosterols. These can compete with endogenous or dietary cholesterol for reabsorption and re-circulation via the bile pathway. This can help flip the balance into the favor of HDL-cholesterol, with a beneficial heart-disease risk reduction. Examples of phytosterol sources are avocado and chia seeds.
Omega (w)-3 Fats
A type of polyunsaturated fatty acid, with a double bond at the -3 carbon position. The most talked about fats currently are w-3 and w-6. Both are essential for life processes; however, today’s diet provides an overabundance of w-6 over w-3 fatty acids (estimated ratio of 6:1). In order to try to balance out the ratio to the ideal 1:1, dietary experts recommend focusing on w-3 consumption from foods and supplements.
The best studied w-3 acids are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). EPA plays a major role in modulating the inflammatory and blood clotting pathways, while DHA is a structural component in many human organs, including the retina, cerebral cortex, and sperm. Research has shown health benefits of w-3 acid consumption in the following conditions: multiple sclerosis, prostate cancer, postpartum depression, mental health and memory, cardiovascular health, Alzheimer’s disease, vision loss, Schizophrenia and psychotic disorders, and fetal development. (8)
The richest source of w-3 acids are oily fish, such as anchovies, herring, sardines, salmon, trout and mackerel. Another ocean dweller, the crustacean called Arctic krill, is also abundant in EPA and DHA, with the added benefit of astaxanthin, which gives the oil a red hue. Astaxanthin is a powerful antioxidant and antiinflammatory agent, especially beneficial for eye and heart health. (9) Plant-based foods contain the precursor to w-3, called alpha-linolenic acid (ALA), which gets converted into EPA and DHA after ingestion. However, since the conversion is only about 5% of total ALA, the plant-based diet should be geared to provide high sources of ALA-rich foods or supplements. The richest sources of ALA include algae, walnuts, chia seeds, hemp seeds and flax seeds. (10)
As mentioned, these are unsaturated fatty acids with double bonds in a “trans” position, with carbon chains on either side being in an opposite configuration (i.e. top position vs. bottom). This creates a “straight” chain, while the “cis” configuration introduces a bend in the chain. The trouble with these type of bonds is that they are unstable, and require little energy to break. They can be disturbed and manipulated easier than other bonds, and are therefore a target for food processing. Synthetic methods can add hydrogens back into these unsaturated bonds, a process called “partial/full hydrogenation.” This turns the oils solid at room temperature and thereby extends shelf life. (11) Examples of this are margarine and any packaged processed junk food, such as ding-dongs. Margarine was a highly popular substitute for butter in the age of saturated fat shaming. It was traditionally made by emulsifying beef fat with water or milk, but for economic reasons partially hydrogenated vegetable oils soon replaced the beef fat. (12)
Natural trans fats occur in meat and dairy from animals such as cattle, sheep and goats. They are formed as a result of bacteria digesting grass in the stomach of such animals. These fats comprise less than 9% of total fat in these animal products, with no negative health effects observed. However, there is a lot of observational and clinical evidence that artificially made trans fats negatively affect cholesterol levels. More specifically, they seem to elevate LDL levels while HDL levels are unchanged, leading to a higher LDL and total cholesterol ratio as compared to HDL. Human studies show elevated risk to heart disease, while animal studies also show an increase in insulin resistance and metabolic changes. Trans fats have also been linked with increased inflammatory markers in studies. (13)
Since it has been elucidated that trans fats are dangerous to heart health, and the real culprits for plaques and complications, the American Heart Association (AHA) has recommended to limit trans fat consumption to under 2 grams per day. The Food and Drug Administration (FDA) banned partially hydrogenated fats from most processed goods, but small quantities of trans fats still make their way into most packaged foods. Levels less than 0.5 grams per serving are not required to be written on package labels in the US; in fact manufacturers can label these as “trans-fat-free.” (14)
(1) Soult, Allison. 14.2: Lipids and Triglycerides. Chemistry Libre Texts. Sept 8, 2019. https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_14%3A_Biological_Molecules/14.2%3A_Lipids_and_Triglycerides
(2) Saely C, H, Geiger K, Drexel H: Brown versus White Adipose Tissue: A Mini-Review. Gerontology 2012;58:15-23. doi: 10.1159/000321319
(3) Andreone BJ, Chow BW, Tata A, et al. Blood-Brain Barrier Permeability Is Regulated by Lipid Transport-Dependent Suppression of Caveolae-Mediated Transcytosis. Neuron. 2017. 94(3):581-594.e5. ISSN 0896-6273 https://doi.org/10.1016/j.neuron.2017.03.043.
(4) Yeagle PL (October 1991). “Modulation of membrane function by cholesterol”. Biochimie. 73(10): 1303–10. doi:10.1016/0300-9084(91)90093-G. PMID 1664240.
(5) Incardona JP, Eaton S (April 2000). “Cholesterol in signal transduction”. Curr. Opin. Cell Biol. 12 (2): 193–203. doi:10.1016/S0955-0674(99)00076-9. PMID 10712926.
(6) Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 26.4, Important Derivatives of Cholesterol Include Bile Salts and Steroid Hormones. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22339/
(7) Ganellin, RC.“Chapter 15 – Discovery of the cholesterol absorption inhibitor, ezetimibe.” Introduction to Biological and Small Molecule Drug Research and Development. Elsevier, 2013 (Pages 399-416). https://doi.org/10.1016/B978-0-12-397176-0.00015-7.
(8) Brazier, Yvette. “Can fish oils and omega-3 oils benefit our health?” Medical News Today. Dec 20, 2017. https://www.medicalnewstoday.com/articles/40253.php
(9) Pearson, Keith. “Krill Oil vs Fish Oil: Which Is Better for You?” Healthline. Jan 9, 2018. https://www.healthline.com/nutrition/krill-oil-vs-fish-oil
(10) Link, Rachael. “The 7 Best Plant Sources of Omega-3 Fatty Acids.” Healthline. Jul 17, 2017. https://www.healthline.com/nutrition/7-plant-sources-of-omega-3s
(11) Marchand, V. “Trans fats: What physicians should know.” Paediatrics & child health vol. 15,6 (2010): 373-8. doi:10.1093/pch/15.6.373
(12) Klonoff DC. “Replacements for Trans Fats – Will there be an oil shortage?” J Diabetes Sci Technol. 2007 May; 1(3): 415–422. PMID: 19885099
(13) Leech, Joe. “What Are Trans Fats, and Are They Bad for You?” Healthline. Jul 30, 2019.
(14) Remig V, Franklin B, Margolis S, Kostas G, Nece T, Street JC.Trans fats in America: a review of their use, consumption, health implications, and regulation. J Am Diet Assoc. 2010 Apr;110(4):585-92. doi: 10.1016/j.jada.2009.12.024