Apparently, the idea that seed oils are unhealthy originated with a 'health' blogger, then it got picked up and amplified on social media, to the point that it has become widely accepted. The evidence doesn't support this idea. Here's a comment from Johns Hopkins School of Public Health:
Some wellness influencers warn against consuming seed oils, blaming them for a range of health problems and characterizing them as toxic. Scientific studies consistently show otherwise.
The science actually does show that fat burning produces more toxic metabolites, and that polyunsaturated fats produce more toxic metabolites outside of the proper chain of enzymes that are designed to oxidize fats purposely for ATP generation. If you look into the actual chemistry involved in our metabolism, the dangers of burning fats as a primary energy source, as well as the added consequences of primarily burning polyunsaturated fats (seed oils) becomes clear.
Fats are a slow burn fuel. They sustain us through fasting (which we do every night), slim times, etc. They are not a high-burn source of fuel. Less ATP is generated in a given unit time by burning fats, than when burning carbs.
Our bodies, well, our cells, run on ATP. ATP is produced in mitochondria, by processing Acetyl-CoA in the Citric Acid Cycle (often called the Krebs Cycle.) Many source compounds can be processed through various enzymes to produce Acecyl-CoA. The primary fuel for producing this, and thus producing ATP, is glucose, and secondarily fructose. We produce far more ATP from these, than anything else. Fats can also be converted into Acetyl-CoA through more complex processes involving many enzymes, but the process is slower, produces less ATP. We can also produce Acetyl-CoA from proteins and even base pairs (i.e. our DNA)...which generally only really occurs when we are starving.
While both carb and fat burning produce Acetyl-CoA which then enters the mitochondria to produce ATP, the byproducts of turning carbs vs. fats into Acecyl-CoA differ. Burning carbs is cleaner, maintains the necessary secondary compounds NECESSARY to keep our mitochondria producing ATP at a high rate (and this is critical, when ATP production lowers everything in our bodies suffers). These compounds include NADH, FADH2, and CO2. CO2 is not just a byproduct of metabolism, its actually a critical component of sustaining the necessary reactions and charge gradient in our mitochondria and keeping the ETC (electron transport chain) moving. The key trait, actually, is the RATIOS of FADH2/NADH. Burning carbs maintains these compounds in the proper balance, burning fats does not (the ratio is higher with fat burning). Burning fats, because these secondary compounds end up imbalanced, then tends to produce a GREATER amount of ROS (reactive oxygen species). Fat metabolism tends to create what is often termed a "traffic jam" in the ETC (electron transport chain), particularly at Complex I. This slows the process, reduces the rate of production of ATP, and in the long run leads to increased production of ROS.
There is always some ROS production, which antioxidants generally sweep up, but when ROS production becomes excessive, then those very species will begin to break down our mitochondria themselves, which in the long run will cause severe problems. So just on its face, burning fats is less effective, less efficient, and long term will produce more damaging compounds to our mitochondria and cells, than burning carbs. Our cells were primarily designed to burn carbs, not fats. This is born out in the chemistry, and the fundamental necessity of a high rate of ATP production for our cells to remain healthy and vital.
The problem with polyunsaturated fats, is that their double bonds allow them to be arbitrarily oxidized, pretty much anywhere. Where saturated fats are far more stable, and will generally be oxidized initially in the ER (endoplasmic reticulum) before those metabolites get shuttled off to the micochondrial matrix for beta-oxidation, polyunsaturated fats are unstable. Arbitrary oxidation of PUFA will often leave fragments of the HC tail behind. These fragments are usually highly reactive, and when your blood stream is full of them, they can cause a significant amount of damage. These toxins can enter other tissues as well and cause additional problems.
Another issue with polysunsaturated fats is they are ill-suited for membrane structures. Polyunsaturated fats tend to be long chain fatty acids, and the double bonds make them weak and "floppy." When used to build membranes, those membranes tend to be weak as well as highly porous, allowing compounds to leak through them outside of the explicit dedicated channels designed for compound transport (i.e. Vacuoles or enzymes embedded in the membrane.) When used for the membranes of mitochondria, they allow electrons and protons (H+) to leak through the membrane. A charge gradient between the mitochondrial matrix (inner membrane space) and the inter-membrane space, is ESSENTIAL to the proper operation of ATPSynthase, the enzyme responsible for actual production of ATP from ADP. The ETC, electron transport chain, enzymes are embedded in the inner membrane, and act as a pump for electrons, transferring them from the inter-membrane space to the inner membrane space. Negative charge, electrons, accumulates in the inner membrane space or "matrix" while H+ ions (protons) accumulate in the inter-membrane space. When our primary source of fats is polyunsaturated, those fats are used during cell division and the genesis of mitochondria for their membranes. Polyunsaturated fats are highly permeable, and when they are the primary or even sole lipid used in mitochondrial membranes, the charge gradient will degrade or even disappear, at which point ATP production STOPS. I shouldn't have to explain how bad that is...
So, sorry...the science,
the actual chemistry, absolutely points to seed oils being detrimental and even dangerous for human consumption in anything beyond very minor quantities. There are actually a multitude of reasons why seed oils, polyunsaturated fats, PUFA, are not only not healthy, but dangerous and ultimately deadly, if we consume too much, fail to consume saturated fats (which are NOT bad, in fact they are VASTLY more healthy than polyunsaturated fats
for humans!! See the Rat vs. Human Disparity Conundrum in scientific testing!), and fail to consume carbohydrates in sufficient quantity given they are by far the best source of fuel to produce ATP compared to alternatives (fats, proteins, DNA).
NADH vs. FADH2
NADH and FADH2 are both electron carriers that donate electrons at the electron transport chain (ETC), allowing for the production of ATP. NADH donates electrons at complex I of the ETC, whereas FADH2 donates electrons at complex II, and these complexes compete for the same electron acceptor, ubiquinone.
Glucose oxidation produces around 25% more NADH and half as much FADH2 as fat oxidation. Together, this leads to a ratio of FADH2 to NADH that is around 2.5 times lower than that of fat oxidation (
9,
10). This difference has substantial effects that extend throughout the processes of mitochondrial respiration.
Because FADH2 donates electrons at complex II, downstream of complex I, it reduces the amount of ubiquinone available to accept electrons at complex I, leading to a buildup of electrons at complex I. This results in two major problems.
For one, this increases the electron leakage at complex I, which increases the production of ROS, specifically superoxide (9, 10, 11).
ROS are a major cause of cellular oxidative stress, and as I’ve already mentioned, damage the cell and inhibit energy production.
Second, the buildup of electrons at complex I reduces the donation of electrons by NADH, leading to a buildup of NADH and a decrease in the ratio of NAD+ to NADH (9, 10, 11, 12).
The ratio of NAD+ to NADH is a major controller of mitochondrial respiration and is also tied to aging, cancer, diabetes, neurodegeneration, and many other diseases (
13,
14,
15).
A low NAD+/NADH ratio inhibits isocitrate dehydrogenase (IDH), the rate-limiting step of the TCA cycle (aka Krebs or citric acid cycle). This slows down the activity of the TCA cycle and leads to a buildup of citrate, which inhibits phosphofructokinase (PFK), the rate-limiting step of glycolysis, while also causing a buildup of ACoA (
11).
The low NAD+/NADH ratio also inhibits pyruvate dehydrogenase (PDH), the rate-limiting-step that connects glycolysis to the TCA cycle, and the buildup of ACoA further inhibits PDH (
11). This directs pyruvate towards lactate rather than ACoA.
The inhibition of glucose oxidation by fat oxidation through these mechanisms is a feature of the Randle cycle and is responsible for the insulin resistance seen in response to high-fat meals and diets (
16). This is, of course, an adaptive response to using fat for fuel and is not a problem per se.
However, in this state, glycolysis is inhibited to a lesser degree than PDH, resulting in an increased production of lactate which can cause problems of its own (
11,
17,
18). And, the decrease in the NAD+/NADH ratio still reduces the activity of the TCA cycle through the inhibition of IDH, which slows energy production.
Overall, fat oxidation drastically reduces the efficiency of energy production, causing much less energy to be produced while increasing ROS production, which has a damaging and destabilizing effect (11, 19).
I'll leave it here. This isnt' really the forum for this. However, there is a lot of bad, old science. Some science is conducted well, some science is not, and some science is twisted to confirm the preconceived notions of an agenda. There is a lot of recent science that very clearly demonstrates the problems with modern, seed-oil infused diets. Such as the snippet above. There NEEDS to be a deeper discussion of seed oils and how radically detrimental they are to human health. Not at some abstract level, but at the core level of the ACTUAL CHEMISTRY and the fundamental nature of cellular function in a human being. The entire western world is unhealthy, and getting unhealthier. One of the primary reasons for that, is seed oils. Its not the sole reason, but its a HUGE reason. Find the right science, and be enlightened.
Cooking effectively renders proteins edible, whereas what I was thinking of was legitimate rot, via more complete breakdown of the proteins into fragments, and consumption by bacteria (or fungi) and the ultimate waste products from them. 
