The Truth About Fats: It Depends on the Fat, and on You

Why the low-fat era got it wrong, and why the correction can go too far

For decades, fat was the villain. We were told to fear it, to choose low-fat everything, to swap butter for margarine and whole foods for processed "diet" versions. That advice was wrong, and we're still cleaning up the damage it did. The problem though is that in discovering that fat isn't the enemy, it's tempting to swing all the way to "all fat is wonderful for everyone." That isn't true either. The real answer, like so much in health, is more specific. It depends on the type of fat, and it depends on you.

So let's actually understand fat, what it does in your body, which fats serve you, and why the right amount and type is different for different people. Once you understand what fats are for, the choices make sense.

What fat actually does in your body

Fat has been treated as little more than stored calories, something to burn off or avoid, but fat is one of the most essential and hardworking substances in your entire body. Let me show you everything it's quietly doing.

First, fat is a preferred fuel. Your body can run beautifully on fat, and in many ways it's a cleaner, steadier energy source than sugar (glucose), giving you lasting fuel without the spikes and crashes. Much of your body, including your heart, kidneys, and liver actually prefer fat for energy.

Second, and this is the one most people never hear, every cell in your body is wrapped in a membrane made largely of fat. That membrane isn't just a wall. It's where an enormous amount of the cell's business happens, what gets in, what stays out, how cells communicate. The quality of the fat you eat literally becomes the quality of these membranes. Eat healthy fats, and your cells are wrapped in flexible, responsive membranes. Eat damaged, processed fats, and those go into your membranes too. You are, quite literally, built from the fats you eat.

Third, your brain is about sixty percent fat. It needs fat to build itself and to function, which is why certain fats are so critical for memory, mood, and clear thinking. We'll come to the most important one shortly.

Fourth, your hormones depend on fat. Many of your hormones, including the sex hormones and your stress hormones, are made from cholesterol, which is a fatty substance. This is a big reason the war on dietary fat and cholesterol backfired, because you need these raw materials to make the hormones that keep you balanced and well.

Fifth, fat is how you absorb entire categories of nutrients. The fat-soluble vitamins, A, D, E, and K, cannot be absorbed without fat. So, the fat-free salad dressing you were told to choose and just steaming your vegetables actually prevented you from absorbing the nutrients in those vegetables. Fat isn't getting in the way of nourishment. It's often what unlocks it.

Once you see all of this, the idea of a low-fat diet starts to look not just mistaken but genuinely harmful. Fat isn't a reluctant indulgence. It's foundational.

Saturated fat: good for most, but not for everyone

Now to the fat everyone argues about. For more than fifty years we were told saturated fat, the kind in butter, meat, and coconut, clogs your arteries and causes heart disease. Much of that belief is traced back to flawed and selective research decades ago with a man named Ancel Keys, and the science since has largely failed to support the simple claim that saturated fat causes heart disease. So, for most people, good quality saturated fat from real food is not the villain it was made out to be. It's a stable, useful fat, and your body knows exactly what to do with it.

But here is what almost no one tells you, and it's the part I care about most. "Saturated fat is fine" is true for most people, and genuinely not true for some. The difference is largely in your genes.

Some people carry variations in genes that govern how they handle fat, and for them, a diet high in saturated fat really does raise their risk. The best known is a gene called APOE. People with a particular version of it, APOE4, tend to respond to saturated fat with sharper rises in cholesterol and higher risk, for both their heart and their brain. There's also a gene called APOA2, where a certain variation is linked to how strongly saturated fat affects body weight, metabolism and inflammation. For a long time, the worry about saturated fat was all about it raising cholesterol numbers and it still is, but I think there's more going on here than cholesterol. I suspect the deeper issue, at least for people with these genetic variations, is inflammation. With the APOE4 variant, it is well established that carriers tend to show a more inflammatory profile and respond to saturated fat with both higher cholesterol and more inflammation. With APOA2, the picture is newer but pointing the same way: studies are finding that people with the susceptible variation of this gene produce more inflammatory markers when they eat saturated fat.

This is exactly why blanket advice fails. Tell everyone to eat all the saturated fat they want, and you'll help some people and harm others. Tell everyone to avoid it, and you'll needlessly deprive the many to protect the few. The truth is that the right amount of saturated fat is personal, and it can be guided by your genetics. This is something I work on directly with people, looking at how their individual genes shape what they should eat, because the goal was never a rule for everyone. It's the right approach for you. If you've ever felt confused because one expert swears by butter and another warns against it, this is often why. They may both be right, for different people.

Olive oil: the fat I want everyone to eat more often

If there's one fat I wish everyone would use more generously, it's good olive oil. When I say olive oil, I always mean extra virgin, cold pressed, and ideally organic, because the cheap, refined, or blended versions lose much of what makes olive oil so special. The quality genuinely matters here.

Real extra virgin olive oil is one of the most powerfully anti-inflammatory foods we have, and since so much of chronic disease is rooted in inflammation, that's no small thing. It contains a compound called oleocanthal that acts in the body a little like ibuprofen, calming inflammation naturally. I've seen the benefits of good olive oil again and again, in heart health, in cholesterol, in skin, in the gut, and even in easing pain. It's one of the simplest, most powerful additions most people can make to how they eat.

A word on heat, since people always ask. Good extra virgin olive oil is actually more heat-stable than its reputation suggests, because those same protective polyphenols help shield it when it's warmed. Personally, I like to keep it around 350 degrees or less when I cook with it. That's a safe temperature, maybe even extra safe, and plenty of everyday cooking happens right around there. If you go a bit higher now and then, it's okay. But here's my real guidance: eat the majority of your olive oil raw. Any heating costs it some of its nutritional value, so drizzle it over finished dishes, over vegetables, into dressings, where its full benefit stays intact. Treat it as a food in its own right and not just as a cooking oil.

DHA: the fat your brain is built from

I've mentioned DHA a few times in this series, and here is where it gets its due. It may be the single most important fat for your brain.

DHA is an omega-3 fat, and it's a structural material, actually built into the membranes of your brain cells and your eyes. It keeps those membranes fluid and helps your brain cells communicate, which is a real part of how memory, focus, and mood work. It's also deeply anti-inflammatory, including in the brain. When people run low on DHA over time, the brain simply can't function or maintain itself the way it should.

Here's the catch, and it's important. The DHA your brain needs comes almost entirely from seafood: fatty fish like salmon, sardines, and mackerel. There is a plant form of omega-3, called ALA, found in foods like flax and walnuts, and you'll often hear it offered as an alternative. But your body converts ALA into usable DHA very poorly, so poorly that it barely counts. This is why I'm cautious about relying on plant sources for something this important. If you want to protect your brain, eat the fatty fish. I cannot stress enough how important this is for your brain!

The oils to walk away from

Now for the fats I want you to be wary of, because this is where a lot of quiet harm is done. I'm talking about the industrial seed oils, the ones often sold as "vegetable oil," along with canola, soybean, corn, cottonseed, safflower, sunflower, and grapeseed oil. They're in nearly every processed and packaged food, and in the fryers of almost every restaurant.

My objection to them is simple, and it's really about how they're made. Stop and think about how you would get oil out of a corn kernel or a soybean. You can't just press it the way you squeeze oil from an olive. These oils are forced out using high heat and industrial chemical solvents, and then they have to be degummed, bleached, and deodorized, more heat and more processing, just to become something you'd be willing to put in your mouth. By the time that oil reaches the bottle, it has been through a factory process that has nothing to do with food. I simply don't want to eat an oil that required chemicals and bleaching to be made edible, and I don't think you should either.

There's a second problem that makes it worse. These oils are rich in fragile fats that are easily damaged, and all that heat and processing, plus the heat when you then cook with them, causes them to oxidize. Oxidized fats are inflammatory and are exactly the kind of damaged material you don't want building into those cell membranes we talked about earlier. On top of that, we now eat these oils in enormous quantities, which has badly skewed the balance of fats in our diet in a direction that promotes inflammation. So you have a fragile, heavily processed oil, often already damaged before you buy it, eaten in amounts no human ever ate before the last century. That's not a food I can recommend.

A quick word on avocado oil, since it gets lumped in with the healthy oils. I'm not a fan, and here's why. A whole avocado is a wonderful food. But much of the avocado oil on the market is a different story. Testing has repeatedly found that a large share of avocado oils are rancid before you even open the bottle or quietly cut with cheaper oils. Also, think about all the avocados that are bruised or brown inside. Those don't get thrown away. And much avocado oil is refined for high heat, with some of the same kinds of processing I just described. The fruit is great. The oil is a gamble.

The fats to welcome back

So what should you actually use? Happily, the good options are the simple ones…the fats you could more or less get without a factory.

Extra virgin, cold pressed, organic olive oil is my first love, mostly raw, as we covered. Virgin coconut oil is another favorite, stable and nourishing. Grass-fed butter and ghee are wonderful for many people, and butter in particular handles heat beautifully, which makes it a great choice for cooking. Tallow, the rendered fat of beef, is another traditional cooking fat that's stable and well suited to higher heat. Lard can also be used for higher heat, but it must come from pastured pigs because pigs are monogastric, so their fat reflects more of what they are fed than a cow’s fat does. So, if they are fed corn and soy, like most are, their fat will contain those fragile polyunsaturated ones. And then there are the fats that simply come with real food: the fat in healthy meat and eggs, the DHA in fatty fish, and whole foods like olives, avocados, nuts, and seeds eaten as they are.

Notice the pattern. These are fats you can picture being made. You can see butter churned, an olive pressed, fat rendered from meat, oil squeezed from a coconut. There's no hexane, no bleaching, no deodorizing. That simple test, could I imagine making this in my own kitchen, will steer you right more often than almost any label.

One note, true to everything I believe: it always depends on the person. Grass-fed butter is a gift for many, but someone with the genetic fat-metabolism variations we talked about, or a true dairy sensitivity, will do better leaning on olive oil and fish instead. As always, the goal isn't a rule for everyone. It's the right fats for you.

A quick word on fat as medicine

There's one more thing worth planting here, because it surprises people: fat can be used therapeutically. The ketogenic diet, which shifts the body to running primarily on fat, has become a genuine prescription-style tool for certain conditions, and the results in some cases are remarkable, including for the brain. I've seen it help with a range of serious issues, but that's a big topic that deserves real care and its own discussion, so I'll give it the full treatment in a later post on different ways of eating. For now, just hold onto the idea that fat isn't only food. In the right situation, it can be powerful medicine.

The real lesson

As with so much in nutrition, we got fat wrong by being all-or-nothing. First we feared all of it. Now some would have us believe all of it is equally wonderful. Neither is true. Fat is essential, foundational, and deeply nourishing. Good saturated fat is fine for most, though not for everyone. Olive oil is a gift. DHA is non-negotiable for your brain. And the right balance for you depends on your body, your genes, and your health.

That's the thread I keep coming back to, and it's worth saying plainly: stop looking for the one rule that applies to everyone, because it doesn't exist. Understand what these foods actually do, understand your own body, and let that guide you.