Why Hydrogenated Oils Are Harmful - The Chemistry of Heat and Chemical Change

Hydrogenated oils are the reason cookies stay flaky, margarine spreads easily, and fried foods taste crispy even after sitting out. They’re cheap, stable, and practical. But the chemistry behind them? That’s where things get messy. The very process that makes them useful in food manufacturing also makes them harmful inside your body.

The Chemistry of Hydrogenation

Natural vegetable oils are made mostly of unsaturated fatty acids. These fats contain carbon-carbon double bonds that give them a bent shape when in the natural cis configuration. That bend keeps the molecules from stacking tightly, which is why olive oil is liquid at room temperature.

Differences Between Saturated and Unsaturated fatty acids.

Hydrogenation is an industrial process where hydrogen gas is forced into these oils at high temperature, using a metal catalyst such as nickel. Two major changes happen here. First, some double bonds pick up hydrogen atoms and become single bonds. This makes the fat more saturated, which makes it firmer. Second, some double bonds flip from cis to trans configuration. This straightens the molecule, making it behave like a saturated fat, even though it’s technically still unsaturated.

That flip is what produces trans fats unnatural fatty acids like elaidic acid that don’t exist in natural oils. On paper, they look almost identical to healthy fats. In the body, they act like saboteurs.

What Heat Does to Oils

Hydrogenated oils don’t stop changing after they’re made. Once you use them for frying, they undergo another wave of chemical reactions. At frying temperatures (around 190 °C), the oil is in constant transformation:

• Oxidation: When oils, especially those rich in unsaturated fatty acids, are exposed to heat, light, or air, the double bonds in their structure are highly vulnerable to attack by oxygen. This reaction forms unstable peroxides, which then break down into aldehydes, ketones, and other reactive compounds. Not only do these byproducts create the characteristic "rancid" odors and off-flavors, but they can also contribute to oxidative stress in the body, damaging cell membranes and DNA over time.
• Hydrolysis: During frying or prolonged heating, water present in the food interacts with the triglycerides in the oil. This reaction splits the triglycerides into free fatty acids and glycerol. Free fatty acids lower the smoke point of the oil, causing it to smoke and degrade faster, while glycerol can dehydrate further into acrolein, a compound with a sharp, irritating smell and potential health risks. This is why old cooking oil tends to taste bitter and harsh.
• Polymerization: Under continuous heating, some fat molecules bond together to form larger, heavier compounds. This polymerization thickens the oil, turning it sticky and viscous, while also giving it a darker appearance. The gummy residues left behind can coat cooking equipment, making cleanup difficult. In food, these polymerized products can alter texture and reduce nutritional quality.
• Fission: Extreme heat or prolonged use can cause some fat molecules to break apart entirely, producing smaller fragments such as aldehydes, hydrocarbons, or even toxic compounds like acrylamide (depending on the cooking medium). These breakdown products not only contribute to unpleasant flavors and odors but can also pose risks to human health if consumed regularly.

This is why old frying oil becomes darker, thicker, and develops unpleasant flavors. Experiments show that while hydrogenated oils are slightly more resistant to this breakdown than non-hydrogenated ones, they come with the trade-off of much higher trans fat content.

Why Your Body Struggles with Trans Fats

The real danger isn’t in how these oils behave in the fryer it’s in how they behave once you eat them. Trans fats affect your body on several levels:

• They raise LDL cholesterol , the “bad” cholesterol that clogs arteries and lower HDL cholesterol, “good” cholesterol that clears fats away.
• They block the metabolism of essential fatty acids like linoleic and linolenic acid, which your body needs to make prostacyclin (to keep blood vessels open) and thromboxane (to clot when necessary). With prostacyclin suppressed, your blood is more likely to clot inappropriately.
• They stiffen cell membranes. Cis fats keep membranes flexible; trans fats make them rigid, disrupting how nutrients move in and waste moves out.
• They trigger inflammation, raising markers like C-reactive protein (CRP), which are directly linked to atherosclerosis and heart disease.

The World Health Organization estimates that industrially produced trans fats contribute to more than 278,000 deaths worldwide each year. That’s not just theory, it’s chemistry showing up in public health data.

Why They Were So Popular

If they’re so dangerous, why were hydrogenated oils used for decades? Convenience.

• They last longer on the shelf without going rancid.
• They give baked goods and fried foods appealing textures.
• They cost less than butter or tropical oils.

For food manufacturers, they were a dream ingredient. For consumers, they were a hidden hazard.

The Way Forward

Now that the risks are undeniable, many countries have restricted or banned partially hydrogenated oils. The WHO recommends keeping trans fats below 1% of daily calories, that’s about 2.2 grams a day for a typical diet.

Food scientists and manufacturers have moved toward alternatives:

• Polyunsaturated oils like sunflower, soybean, and corn oil.
• Monounsaturated oils like olive and canola.
• Interesterified fats, where fully hydrogenated oils (which don’t contain trans bonds) are blended with liquid oils and chemically rearranged to create the right texture without producing trans fats.

Hydrogenated oils were an industrial solution to food stability, but inside the human body, they behave like a problem waiting to happen. The chemistry of hydrogenation and heat turns natural, flexible fats into rigid, disruptive molecules.

Yes, they make pie crusts flaky and fries crispy. But they also clog arteries, stiffen membranes, and raise the risk of heart disease.

So, when you see “partially hydrogenated oil” on an ingredient label, remember: that’s not just oil. That’s a chemical transformation your body was never designed to handle.

Unlike many commercial cookies that rely on hydrogenated oils and refined ingredients, No Spike cookies by B’spoke are made differently on purpose. Hydrogenated oils are commonly used in packaged snacks to extend shelf life, but they introduce trans fats, compounds linked to inflammation, oxidative stress, and a higher risk of cardiovascular disease. On top of that, when hydrogenated or unstable oils are baked or fried, they undergo reactions like oxidation, hydrolysis, polymerization, and fission, producing rancid flavors and sometimes harmful byproducts

No Spike avoids all of that.

• We use blanched almond flour, not processed wheat plus shortening, which means no hidden trans fats.
• Instead of cheap fillers, you get protein and 21 g of prebiotic fiber, nutrients that stabilize blood sugar rather than trigger a crash.
• Each cookie contains 128 mg of magnesium, a mineral that supports energy metabolism and muscle function.
• Most importantly: No hydrogenated oils, no empty calories, no sugar spike.

That’s why No Spike cookies aren’t just a snack, they’re functional food designed to fuel your body, care for your metabolism, and still satisfy your cravings.