THE SKINNY ON FAT: The Complete Simpleton's Guide to Dietary Fat (PART 1)

THE SKINNY ON FAT: The Complete Simpleton's Guide to Dietary Fat (PART 1)

By Shane Robert

In the world of food and nutrition, macronutrients (protein, carbs, fats) have taken on roles well beyond their use. Each nutrient has been vilified as evil and the root cause of all diseases, and each has been the star of the show, being considered the most important messianic macronutrient, all the rest be damned. In all instances, these extremes have been wrong. The truth, as is usually the case, is somewhere in between, and the classic “it depends” fits perfectly. The good or evil depends on the person and the circumstance.

Fat’s Longstanding Bad Reputation

Perhaps more than any other, fat has been saddled with the burden of evil for a very, very long time. Though carbs have been at the center of attention, at various times (for the last 20-30 years), fat has largely been considered bad for the better part of 80 years, with little time off for good behavior. As the carbs-are-bad crowd has gained in popularity, there has been a slight reduction in the anti-fat crusaders as they begrudgingly admit that not all fat is bad and, indeed, some is even necessary. Despite giving slightly, many have dug in deeper and continue to push a low-fat agenda that would seem perfectly at home in a mid-1980s Reader’s Digest article. As lay consumers trying their best to do what is healthy, it can be challenging to know what is right and what is wrong when, in truth, there is a fundamental lack of basic understanding about what fat IS.

What Is Fat, Really?

Most of the fat we eat is in the form of triglycerides (you’re likely familiar with this word after your cardiologist told you yours are too high). A triglyceride is a molecule made of a glycerol (a type of alcohol) backbone with 3 fatty acids. A fatty acid is a chain of carbon atoms with hydrogen atoms attached and a carboxylic acid group (-COOH) at one end. The COOH is what makes them fatty acids (distinguishing them from other types of lipids/fats or hydrocarbons), and is the reactive group that allows the fatty acids to form esters with glycerol. Ester is a fancy way of saying bonding or binding, which it does by bonding an alcohol (in this case glycerol) to the carboxylic acid by losing water molecules. These fatty acids are the part of fat that gives it its structure and function.

How Fat Is Digested and Used

After we eat fat, our body begins to digest it in the small intestine, where bile (from your liver) helps break fat into smaller droplets. Enzymes, primarily lipase, break triglycerides into the constituent parts of free fatty acids and glycerol. These are then absorbed by the intestinal cells and packaged into particles called chylomicrons. Chylomicrons move through the lymphatic system and bloodstream to deliver fat to tissues. Your body either burns these fats for energy or, if energy availability is higher than needed, stores them in fat cells for later use. The leftover remnants of the chylomicrons are sent to the liver.

Fat’s Role in Energy and Cell Structure

Fats' unwarranted bad reputation aside, it plays a vital role in human health. First and foremost, fat is the most energy dense macronutrient and provides 9 calories per gram, more than double the energy of 4 calories per gram in carbs or protein, which makes it very efficient for providing energy, something that our calorie spare ancestors benefited greatly from, even if modern humans are lucky enough to have the opposite problem. In addition to energy, fat helps to build and maintain cell structure. Every cell in your body has a cell membrane, and fat is a major component of it. These fats help make membranes flexible, fluid, and selectively permeable, meaning they control what enters and leaves the cell. Fat also anchors important proteins and receptors on cell surfaces, which are essential for signaling and communication between cells.

Hormones, Vitamins, and More

Fats are critical for making steroid and sex hormones like estrogen, testosterone, and progesterone, in addition to stress hormones like cortisol (which, like fat, and despite media fearmongering, is not all bad). Cholesterol, a molecule related to fat, is the building block for many of these hormones, which variously regulate growth, reproduction, metabolism, mood, and oh so much more. Without fat in your diet, your body would struggle to absorb many essential nutrients from food or supplements. Fat helps your body absorb the fat-soluble vitamins A, D, E, and K. The importance of these alphabetic vitamins can’t be overstated. Vitamin A helps form and maintain healthy teeth, skeletal and soft tissue, mucus membranes, and skin; vitamin D is needed for bone health, immune function, mood and brain health, gene regulation like cell growth and repair, and muscle function; vitamin K is crucial for blood clotting, bone health, and potentially heart health. 

Fat and the Immune System

Certain fats, not unlike the above-mentioned vitamins,  help regulate inflammatory responses and support immune system activity. Omega-3 and omega-6 fatty acids (more on these two fats later) are involved in creating signaling molecules called eicosanoids, which can either promote or reduce inflammation depending on the body's needs.

Fat and Brain Health

Perhaps the most important role that fat plays in the body is regarding the brain. Human brain tissue is nearly 60% fat by dry weight, and it needs specific fats, like omega-3 fats, to develop and function properly. Fat is vital for the myelin sheath, an insulating layer that surrounds the action potential (axons) of neurons, facilitating rapid and efficient transmission of electrical impulses along nerve cells. Think of this like insulation on an electrical wire. Given the massive role that fat plays in the brain, it should be little surprise that a deficiency in healthy fats has been linked to issues like poor memory, depression, and neurological disorders. 

The Bottom Line

Despite being misunderstood, fat is not just important, it's essential for survival and optimal health. Whether it is through providing energy as a high-calorie, long-term fuel, keeping cells healthy and functional, powering hormone creation, helping our bodies absorb vitamins, supporting memory, mood and nerve signaling, or regulating inflammation and immune response, fat is a deeply integrated part of your biology. Not all fat is the same, however, and some fats are more beneficial than others. 

In part 2, we will cover the different types of fats and the effect they have on our bodies. In part 3, we will discuss how much fat and what types of fats to include in our diet for various goals.