Fat has had a rough few decades. It was the nutrient to cut, count and hide, and many people still see it as empty calories. Biologically, that is backwards: without fat there would be no cells, no sex hormones and hardly any uptake of vitamins A, D, E and K.

For the food industry, that makes oil one of its most valuable ingredients, and keeping it intact one of its toughest problems.

What Fat Actually Is

Scientists call fats, oils and related substances lipids. When we talk about fat or oil, though, we usually mean their main component, triglycerides: a small glycerol backbone carrying three fatty acids. Those fatty acids are simple chains of carbon atoms, and their shape decides how the fat behaves.

In saturated fatty acids the chain is straight, so the molecules pack tightly. That is why butter and coconut fat are solid at room temperature. Monounsaturated fatty acids, typical of olive oil, contain one double bond, which puts a kink in the chain. Polyunsaturated fatty acids contain two or more double bonds, and with all those kinks they stay liquid even in the fridge.

Two more lipid families complete the picture. Phospholipids have a water-loving head and two fat-loving tails, which makes them the natural building material for cell membranes. Sterols such as cholesterol are compact ring structures from which the body makes hormones.

What Fat Does in the Body

It builds every cell. Each of the trillions of cells in the human body is wrapped in a double layer of phospholipids. This membrane separates inside from outside and controls what gets in and out.

It stores energy. One gram of fat holds about 9 kcal, more than twice the 4 kcal of carbohydrates or protein. Fat is also stored almost without water, which makes it the body's most compact long-term energy reserve.

It makes hormones. Cholesterol is the raw material for steroid hormones such as oestrogen, testosterone and cortisol, and for vitamin D.

It carries vitamins. Vitamins A, D, E and K dissolve in fat, so the gut absorbs them together with fat. A carrot salad without any oil delivers far less of its beta-carotene.

It sends signals. Some polyunsaturated fatty acids are turned into eicosanoids, short-lived messenger molecules that help regulate inflammation, blood clotting and many other crucial processes.

It keeps you full. Fat slows the emptying of the stomach, so a meal with some fat keeps you satisfied for longer. It is one reason why ultra-low-fat diets are so hard to stick to.

It carries flavour. Many aroma compounds dissolve in fat. That is why fat carries taste and creates the creamy mouthfeel that is so hard to replace in low-fat products.

The Two Fatty Acids You Cannot Make

The body can build most of the fat it needs from sugar, protein or other fats. So why eat fat at all? Mainly for two fatty acids it cannot make and four vitamins it cannot absorb without fat. The two fatty acids are linoleic acid, an omega-6, and alpha-linolenic acid (ALA), an omega-3. The numbers describe where the first double bond sits, counted from the end of the chain. Humans lack the enzymes to put a double bond in those positions, so both fatty acids have to come from food. That is what makes them essential.

Where to Find Them

Linoleic acid is easy to get. Sunflower, corn and soybean oil are rich in it [1], and so are nuts, seeds, chicken and eggs. Almost nobody runs short.

ALA is harder. The richest sources are flaxseed, chia and perilla oil, where about half or more of the fatty acids are ALA, followed by camelina and hemp oil [2]. Among everyday cooking oils, rapeseed leads with around a tenth [1]. Most other oils, including sunflower, olive and palm, contain hardly any, and neither do most animal fats. Organic milk and meat contain around 50% more omega-3 [3], but a glass of milk still delivers only a small fraction of the omega-3 in a tablespoon of rapeseed oil.

Then there are EPA and DHA, the long-chain omega-3s found in fish, which in turn get them from algae. The body can make them from ALA, but not very well: only a small share is converted, and men convert even less than women [4]. That is why they are called conditionally essential. The body makes some, but often not enough, so food has to supply the rest. DHA is a major building block of membranes in the retina and the nervous system.

Can You Live Without Fat?

Not in the long run. With no fat at all, the body first uses up the essential fatty acids stored in its own fat tissue. Once those run low, a deficiency sets in: dry, scaly skin, hair loss, poor wound healing, low platelet counts, and in children, disturbed growth and development [5]. Doctors learned this the hard way in the early days of intravenous feeding, when patients received fat-free solutions. Babies, with the smallest reserves, are hit first.

Surviving, however, takes surprisingly little. To prevent deficiency, the body needs only about 5 to 8 g of linoleic acid and around 1 g of ALA a day [6]. A small handful of walnuts, about 20 g, contains roughly that much.

But surviving is not the same as living well. On such a minimal amount of fat, meals stop keeping you full, many people struggle with constant hunger and cravings for fatty food, and vitamins A, D, E and K are poorly absorbed. Women on very restrictive low-fat diets can also lose their period, usually because the body is short of energy. Anyone who has tried an extreme low-fat diet knows the feeling. That is why FAO and WHO recommend at least 15% of energy from fat for a normal diet, about 35 g a day on 2,000 kcal [6].

How Much Do We Need?

EFSA recommends that adults get 20 to 35% of their daily energy from fat [7]. On a typical 2,000 kcal day, that means about 45 to 80 g, counting all the fat in food. For orientation: a tablespoon of oil contains about 14 g of fat, a handful of nuts 15 to 20 g, and a whole avocado 20 to 30 g [8].

The essential fatty acids are needed in much smaller amounts: about 9 g of linoleic acid, just over 1 g of ALA and 250 mg of EPA and DHA per day [7]. In practice, a handful of walnuts (about 30 g) covers both linoleic acid and ALA for the day [8]. For ALA alone, a teaspoon of flaxseed oil or a tablespoon of rapeseed oil is enough. EPA and DHA come with one to two portions of oily fish a week, such as salmon, mackerel or herring [7].

EFSA derived the values for linoleic acid and ALA from the lowest average intakes in European populations where no deficiency occurs. So they are best read as a safe level, not an optimum.

The Catch: Essential Means Fragile

The feature that makes these fatty acids essential also makes them fragile. Every double bond is a spot where oxygen can attack, and the more double bonds a fatty acid has, the faster it oxidizes [9]. Linoleic acid has two, ALA three, EPA five and DHA six. That is why fish oil turns rancid so quickly, and why fish oil supplements almost always need additives to preserve them.

You can smell it when it happens. Rancid oil smells of crayons, putty or old paint, and by then the valuable fatty acids are already breaking down. No oil is immune to that. A bottle of olive oil left on the shelf for three years may still be edible, but it will be rancid and nothing you would want to eat or sell.

Lipid Legends keeps oils rich in essential fatty acids stable without refining or additives, using the seed's own polyphenols; to find out what that could mean for your product, write to Polina Novikova at polina.novikova@lipid-legends.com.

References

_{[1]  Codex Alimentarius, Standard for Named Vegetable Oils, CXS 210-1999 (as amended).}

_{[2]  Dubois, V., Breton, S., Linder, M., Fanni, J., Parmentier, M., Fatty acid profiles of 80 vegetable oils with regard to their nutritional potential. Eur. J. Lipid Sci. Technol. 2007, 109, 710-732. DOI: 10.1002/ejlt.200700040}

_{[3]  Średnicka-Tober, D., et al., Composition differences between organic and conventional meat: a systematic literature review and meta-analysis. Br. J. Nutr. 2016, 115, 994-1011; and companion meta-analysis on organic milk, Br. J. Nutr. 2016, 115, 1043-1060.}

_{[4]  Burdge, G. C., Calder, P. C., Conversion of alpha-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reprod. Nutr. Dev. 2005, 45, 581-597.}

_{[5]  MSD Manual Professional Version, Essential Fatty Acid Deficiency. merckmanuals.com}

_{[6]  FAO, Fats and fatty acids in human nutrition: Report of an expert consultation. FAO Food and Nutrition Paper 91, Rome, 2010. fao.org}

_{[7]  EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA Journal 2010, 8(3), 1461. DOI: 10.2903/j.efsa.2010.1461}

_{[8]  USDA FoodData Central (walnuts, avocado, vegetable oils). fdc.nal.usda.gov}

_{[9]  Choe, E., Min, D. B., Mechanisms and factors for edible oil oxidation. Compr. Rev. Food Sci. Food Saf. 2006, 5, 169-186. DOI: 10.1111/j.1541-4337.2006.00009.x}