You have met this patient. She is doing everything right on paper. Her hormones are dialed in, she is finally sleeping, she has cleaned up her exposures. And she still cannot lose the weight. Her thyroid numbers still read a little off. The inflammation will not settle. You pull her labs again, and again they look fine, and you sit there wondering what you are missing.
A lot of the time, part of the answer is sitting on her plate. Not her calories. Not her willpower. The kind of fat she has been eating for the last twenty years.
So let me answer the question the way a provider actually needs it answered, not the way the internet fights about it.
Are seed oils bad for you? The short answer
Seed oils are not poison. The people telling you to throw out every bottle today are overselling it. But they are not harmless either, and the people telling you to pour them on freely are ignoring the mechanism. The real issue is not linoleic acid itself. It is what linoleic acid becomes after it oxidizes inside the body.
Oxidized polyunsaturated fats damage mitochondria. Mitochondria are where your patient makes her steroid hormones. So when a hormone patient is not responding the way your protocol says she should, her fat intake is a reasonable place to look. That part is mechanism, and the mechanism holds up. Whether the long-term outcome trials have caught up to it is a separate question, and the honest answer there is not yet.
What seed oils actually are
Seed oils are the industrial cooking oils pressed from crops. Soybean, canola, corn, sunflower, safflower, cottonseed, grapeseed. They are the base fat in almost everything that comes in a bag, a bottle, or a fryer. If it is shelf stable or served at a restaurant, it is probably built on them.
The fat inside them that matters is linoleic acid, an omega-6 polyunsaturated fatty acid, or PUFA. And we are eating far more of it than we used to. When researchers measured the linoleic acid stored in the body fat of US adults, it had more than doubled between 1959 and 2008, from about 9 percent of fatty acids to over 21 percent (Guyenet and Carlson, Advances in Nutrition, 2015). That is not a minor dietary tweak. It is a structural change in what the modern body is built out of. Before industrial seed oils, most of our fat came from animals, and it was largely saturated. Butter. Beef tallow. That is a recent and fast reversal.
The chemistry that matters: cast iron versus stainless steel
Here is the analogy I use with patients, because the structure is the whole story.
Picture a cast iron skillet in one hand and a stainless steel pan in the other. Cast iron is strong, but leave water sitting on it overnight and by morning it has a coat of rust. That rust is oxidation, raw iron reacting with oxygen. Now do the same thing to stainless steel. It looks the same in the morning. It resists oxidation because its structure is more stable.
Polyunsaturated fat is the cast iron. Saturated fat is the stainless steel. Every double bond in a fatty acid is a reactive site, a spot where oxidation can start. Linoleic acid has two. Saturated fats have zero, which is why you can heat tallow hot without it breaking down, and why a stick of butter can sit out for a month and stay fine. Open a fish oil capsule and leave it on the counter, and it smells rancid in hours. Same chemistry, different speed. That difference is exactly how these fats behave once they are inside a cell.
Why are seed oils bad? It comes down to what linoleic acid becomes
Linoleic acid on its own is not the villain. The trouble starts when it oxidizes and forms a family of byproducts called OXLAMs, oxidized linoleic acid metabolites. These are measurable in blood and tissue, and they are directly hard on mitochondria. In animal work, dietary OXLAMs drove mitochondrial dysfunction, lowered ATP, and triggered inflammatory and cell-death pathways in the liver (Schuster et al., Journal of Lipid Research, 2018).
This is the part clinicians should not skim. Energy is the currency of every cell. Damage the mitochondria and you have backed the patient into a corner that hormones alone will struggle to fix.
The mitochondrial mechanism, and why it reaches your hormone patients
Follow the chain, because this is where it lands. Oxidized fats make the mitochondria less efficient. The cell can no longer pull energy cleanly through oxidative phosphorylation, so it slides toward glycolysis. Glycolysis makes a fraction of the ATP and leaves lactate behind instead of carbon dioxide. Less carbon dioxide means worse oxygen delivery and tighter blood vessels. More lactate means more inflammation. The whole system tips toward the stressed, low-energy state.
And here is the hormone piece. Steroid hormones are made inside the mitochondria. Progesterone, pregnenolone, DHEA, all of them start there. Damage the machinery and you make less of everything, no matter what you prescribed. One 2025 commentary in Frontiers in Nutrition laid this out as an energy model of insulin resistance, tying seed oil intake directly to mitochondrial disruption, metabolic disease, and even cancer (Frontiers in Nutrition, 2025). You do not have to accept every line of that model to see the clinical point. If the mitochondria are struggling, the hormones you are trying to restore are being made in a compromised factory.
Why this shows up in your HRT patients specifically
This is also why it does not resolve on a two-week diet change. Linoleic acid does not clear quickly. It accumulates in fat tissue with a half-life around 680 days, close to two years for levels to fall by half after someone changes how they eat (Guyenet and Carlson, 2015). Worse, stored PUFAs get released back into circulation during stress, fasting, and weight loss. A patient who ate seed oils heavily a year ago is still cycling those fats through her system every time her body burns fat.
So the patient who is estrogen dominant, or stuck hypothyroid at the tissue level despite acceptable labs, or simply not responding to a clean protocol, may be carrying a fat load that is quietly working against you. That is not a reason to stop prescribing hormones. It is a reason to widen the conversation past the prescription pad.
Seed oils and inflammation: the whole-system view
Inside the course, seed oils are number four of what I call the Big Five metabolic disruptors. Studying them in isolation is useful. Studying how they compound with the other four is where the real clinical reasoning lives. Oxidized fats loosen the gut and let more endotoxin into circulation, which is the same recirculation problem behind so much stubborn estrogen dominance (see the estrobolome breakdown). Cortisol then mobilizes stored fat, and if that fat is loaded with linoleic acid, every stress response sends another wave of PUFAs into the blood. This is the metabolic reality that finally made it into a diagnosis when PCOS was renamed PMOS. These disruptors do not act alone. They reinforce each other, and together they push the cell toward the low-energy, inflamed state.
But some studies say seed oils are fine. What gives?
A careful clinician has to sit with the counter-evidence, so let us do that honestly. There is real data on the other side. A 2025 systematic review, in the same journal, looked at seed oils in diabetic and dyslipidemic patients and reported neutral to favorable effects on glucose control and inflammatory markers (Frontiers in Nutrition, 2025). Other recent analyses point the same way. This is a live debate, not a settled verdict, and anyone who tells you otherwise is selling something.
So why do I still take the mechanism seriously? Because of what those studies measure and what they do not. Most track glucose, lipids, and cardiovascular events over months. They are not measuring oxidized metabolites in tissue, steroid production, or thyroid signaling at the receptor over years, and a fat with a two-year half-life does not show its hand in a short trial. The chemistry is not in question. PUFAs oxidize, OXLAMs form, and OXLAMs are hard on mitochondria. Whether the long-term human outcome literature has caught up to that chemistry is the open question. We just watched PCOS get renamed inside our own careers. Reasoning from mechanism is how you stay a step ahead of the revision instead of a step behind it.
What I actually tell patients
None of this is a reason to scare people. We can do real harm by turning a patient into an anxious label-reader who treats a dinner out like a relapse. PUFAs are in almost everything to some degree, and total elimination is neither realistic nor the goal. The goal is a good conversation about fat, held at the right time.
I do not unload this at the first visit. I lead with hormones. Once there is trust, usually over the first few months, I bring in diet with small goals instead of a purge. For cooking, I point people toward stable, mostly saturated fats: butter, ghee, beef tallow, lard, with coconut oil in the mix. Olive oil is a good choice, and a little avocado oil is fine. What I ask them to pull back on is the ultra-processed seed oil, soybean, canola, corn, sunflower, safflower, and to notice that a label reading cold pressed or heart healthy does not change what heat does to a fragile fat. For most patients the biggest exposure is not their kitchen, it is how often they eat out, since seed oil is the base cooking fat almost everywhere.
Which patients are worth prioritizing
You do not have to run this with everyone at once. Spend the effort where the return is highest. The estrogen-dominant patient who is still symptomatic on progesterone. The subclinical or overt thyroid patient. Anyone with an inflammatory or autoimmune picture and no clear source. The patient who is metabolically stuck despite a solid plan. Pull the oxidizing fats out of the equation while you optimize hormones, and you give the metabolism room to actually repair. That is the same root-cause logic behind everything we teach about treating the physiology instead of the symptom.
The question underneath the question
Most providers who end up reading about seed oils are not doing it because they love lipid chemistry. They are doing it because a patient asked, or because they optimized everything and the patient still did not get better, and the tidy answer they were handed in training is starting to feel incomplete.
That discomfort is worth listening to. Seed oils are not the whole story, and they are not a villain to build your practice around. They are one thread in a larger picture of cellular energy. Understanding that thread in isolation helps. Understanding how it weaves through endotoxin, cortisol, estrogen, and thyroid is a different level of clinical reasoning, and it is the level your hardest cases actually require.
Primary sources
Frequently asked questions
Are seed oils bad for you?
They are not poison, and they are not neutral. Polyunsaturated fats oxidize easily, and their oxidized byproducts damage the mitochondria that make your steroid hormones. For a hormone patient who is not responding as expected, a high seed oil intake is a reasonable factor to address.
Why are seed oils bad for hormone patients specifically?
Because steroid hormones are made in the mitochondria. Oxidized linoleic acid impairs mitochondrial energy production, which sits upstream of progesterone, pregnenolone, and thyroid function at the tissue level. Damage the factory and the output falls, regardless of what you prescribed.
What are OXLAMs?
OXLAMs are oxidized linoleic acid metabolites, the byproducts formed when linoleic acid oxidizes in the body. They are measurable in blood and tissue and have been shown to drive mitochondrial dysfunction in animal models.
Which oils count as seed oils?
Soybean, canola, corn, sunflower, safflower, cottonseed, and grapeseed oils. They are the base fat in most processed and restaurant foods.
What should patients cook with instead?
Stable, mostly saturated fats: butter, ghee, beef tallow, lard, and coconut oil. Olive oil is a good everyday choice, and a little avocado oil is fine.
If a patient cuts seed oils, how fast do levels drop?
Slowly. Linoleic acid stored in fat has a half-life around 680 days, so it takes close to two years for tissue levels to fall by half. Stress, fasting, and weight loss release stored PUFAs back into circulation along the way.
Do not some studies show seed oils are safe?
Yes, several recent reviews report neutral or favorable effects on glucose and lipid markers. They tend to measure short-term cardiometabolic endpoints rather than oxidized metabolites or steroid production over years. The mechanism of concern and the outcome data are not yet fully reconciled, which is why this remains an active debate.
If you want a physiology-driven framework for practicing hormone therapy with real confidence, the HRT University Master Course was built to develop exactly that kind of reasoning. Six modules, thirty CEs, jointly accredited through Pinnacle Conference LLC. Not a protocol to memorize. A way of thinking that holds up when the guidelines do not.
You can also hear the full breakdown on the HRT University Podcast.
