Partially vs. Fully Hydrogenated Oils [for Dummies]

We all know trans-fats are bad, and if you’ve been following this blog, you also know that if partially hydrogenated oil appears in a product ingredient list, that means it contains trans-fats.

But what about FULLY hydrogenated oils?

What you need to know:

To understand this hydrogenation stuff, let’s familiarize ourselves with oils and fat. We promise to make this as simple as possible.

Fat is solid at room temperature; Oil is liquid, but some oils are semisolid at room temperature. All oils and fats are composed of fatty acids. Fatty acids are molecules with lots of carbon, oxygen, and hydrogen atoms. They are classified into 2 main types -

  • saturated fatty acids
  • unsaturated fatty acids

The two types of fatty acids are quite similar, with the main difference being the amount of hydrogen atoms they contain. Saturated fatty acids have much more hydrogen atoms in them. It “stiffens them up” into a more solid substance.

Each kind of oil is a combination of various fatty acids, some saturated and some unsaturated. The more saturated fatty acids an oil has, the higher its melting point. In other words, the more solid it tends to be at room temperature. For example, palm oil, which has mostly saturated fatty acids, is semi-solid at room temperature.

Food companies like oils with saturated fatty acids because they have longer shelf lives and in baked goods provide a better texture and mouthfeel. Lard, by the way is also highly saturated.

Unfortunately, cheap oils like soybean and cottonseed are not solid at room temperature. That’s where the brilliant invention of hydrogenation comes in – bombard the oil with hydrogen atoms until it changes its molecular structure.

If you do it just right, you’ll have created an oil that is solid enough at room temperature, yet still spreadable (margarine anyone?) This is called partial hydrogenation. Do it too much and you’ll get a fully hydrogenated oil, a solid slab at room temperature.

The chemical structure of the unsaturated fatty acids after the partial hydrogenation turns them into trans-fatty acids. But if you go all the way, they turn into the more familiar saturated fatty acids.

Welcome to the wonderful world of organic chemistry.

From a health perspective, it turns out that trans-fatty acids (trans-fat) cause serious health issues, much worse than saturated fatty acids (saturated fat). That’s why despite their culinary and economical allure, in the past few years oils with trans-fats are being used in less products. (Unfortunately, plenty of foods still contain partially hydrogenated oils.)

What to do at the supermarket:

Avoid products with partially hydrogenated oils,because of the trans fat. Limit products with high saturated fat values, whether naturally occurring, or through full hydrogenation.


  1. Lefevre M, Mensink RP, Kris-Etherton PM, Petersen B, Smith K, Flickinger BD.
    Predicted changes in fatty acid intakes, plasma lipids, and cardiovascular disease risk following replacement of trans fatty acid-containing soybean oil with application-appropriate alternatives. Lipids. 2012;47(10):951-62.
  2. FAQs about Fats – American Heart Association
  • Lauren Slayton

    I would take butter or coconut oil over that trans stuff anytime though.

  • Dr. Susan Rubin

    This post will bring all the Weston A Price folks out of the woodwork and with good reason. Saturated fat is not the bad boy that mainstream nutritionists make it out to be.

    Oils such as soy, corn and cottonseed are far more hazardous to human health and planetary health.
    I stongly suggest reading The Queen of Fats by Susan Allport and also read The Oiling of America by Sally Fallon/ Mary Enig.

    Why doesn’t the American Dietetic Association know this stuff? It could easily be a question of follow the money. Look how funds them and you’ll have your answer!

  • Ruth

    @Lauren Slayton


    People think Virgin coconut oil is bad because hydrogenated CO is bad (I used to think that). You might want to inform people that it is a real, traditional, food with many health benefits.

  • Dr. Susan Rubin

    As Joan Gussow is fond of saying, “I trust the cows more than the chemists”

  • Tuck

    Dr. Rubin is spot-on. There’s clear evidence that any fatty acid based on the omega-6 linoleic acid is a disaster waiting to happen, whether fully, partially, or non-hydrogenated.

    Dr. Stephan Guyenet at the Whole Health Source blog has done lots of work collecting the literature on the health implications of excessive linoleic acid intake. Trans fats are only the tip of the iceberg.

  • jml

    As a rule of thumb, the more fluid the fat, the healthier.

  • Gene

    I’m surprised there is no mention of “interesterified fat”. Many companies are using it as a substitute for trans-fat (since it does not have to be labeled), and early studies show it is as bad or worse than trans-fat.

  • clc

    All nutritional implications aside; this post was short, sweet, to the point, and very informative. Nicely done.

  • The Table of Promise

    Thanks Dr Rubin–You are totally right. I love The Oiling of America, it is a great article. You can find a link to it at

    I am saddened to hear you say that one should avoid saturated fats even in their natural state. The low-fat diet is a myth. And if you need to eat fat for good health (ie-proper brain function, cell division and other inportant things you can’t see in your body everday) then what are you supposed to eat? Polyunsaturated oils? These oils can be rancid and full of free radicals which actually CAUSE cancer rather than prevent it. I keep them out of my kitchen, and out of the products that I eat and my children eat. We eat natural fats like olive oil, butter, lard, beef tallow and coconut oil.Check out this website, he writes pretty clearly about it:

    Also–Lard is primarily monounsaturated fat just like olive oil, though it has enough saturated fat to remain semi sold at room temperature. Check out this link at Scroll down you can clearly see it has more monounsaturated fat than anything else.

  • Corey

    You all do know that there are amounts of trans-fat naturally occurring in animal (except fish I think) products anyway right? That includes any dairy products, meat products, etc. So technically if you want to avoid all trans-fat you’re gonna have to go vegan… which, as the splinter cell of vegetarianism (the group of people often taking dinner tables hostage across the world), I do not support. Just thought you all should know!

  • Corey

    Edit: Ruminant animal products and also:

    “the NAS dietary recommendations have not recommended the elimination of trans fat from the diet. This is because trans fat is naturally present in many animal foods in trace quantities, and therefore its removal from ordinary diets might introduce undesirable side effects and nutritional imbalances if proper nutritional planning is not undertaken. The NAS has, therefore, “recommended that trans fatty acid consumption be as low as possible while consuming a nutritionally adequate diet”.”

    citation: Food and nutrition board, institute of medicine of the national academies (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). National Academies Press. p. 424.

  • Ofellia Holler

    Both unsaturated fat and saturated fat are in a variety of foods, studies have found that these fats are not created equally. Unsaturated fats can be beneficial to your heart, whereas saturated fats could be detrimental to your cholesterol and your heart. Question is coconut oil do have the same effect? You can check out at

    • Dillon Parker

      While I agree they are not created equally, I have to disagree with your claim that saturated fat contributes to heart disease. Check out this study:; published by The American Journal of Nutrition.

      You have to realize how heart disease occurs. It occurs when plaque is built up in your veins and arteries.

      How does this occur?
      Plaque buildup is caused by cholesterol when it is healing inflammation in your veins and arteries.

      Thing is…
      There are three types of cholesterol.

      The good :)
      HDL-these are normal sized ones. They remove the small cholesterol. A higher number of these decreases your chance for a heart attack.

      THE BAD
      LDL- small and dense, bb-pellet like cholesterol. These are the bad ones. The collect in your veins and arteries, causing plaque.
      Lpa- these are big, fluffy cholesterol. Because of their size, they’re relatively harmless. They tend not to build up.

      I found this on the Atkins website(—Library/Fats/Atkins-Position-on-Saturated-Fat-.aspx):
      “Recent research has focused on the changes in particle size in LDL cholesterol as a response to different diets- this measure is much more sensitive and telling than just the absolute number LDL cholesterol. In the Hays study, all subjects had atherosclerotic Cardiovascular Disease, and all were obese. They were told to consume one half of all calories as saturated fat (primarily red meat and cheese). Fruit and non-starchy vegetables were prescribed in restricted amounts at each meal, but starch was completely forbidden. Both body weight and body fat percentage decreased in the study group, as did triglycerides. But here’s the really key part: though total HDL and LDL did not change, the size of the particles did! With a diet of fully 50% of calories from saturated fat, the patients saw their risk profile change significantly for the better. In fact, 10 of the 23 patients had a profile that indicated metabolic syndrome at the beginning of the study, even though they had been treated with statins. But by the end of the study, and after consuming a diet that averaged 1- 1 ½ pounds of red meat and 2-4 eggs per day, 8 of the 10 metabolic syndrome patients had changed to a low-risk profile!”

      TL;DR: Basically, saturated fats don’t increase your HDL, but they produce more Lpa (neutral cholesterol) rather than LDL (bad cholesterol), decreasing your risk of plaque build up and heart disease.

  • Martin MacDonald

    I’m sure people have already told you but naturally occurring saturated fats pose no health risks. Avoid man made trans fats.

  • laura

    Look at the peanut butter labels for JIF and Skippy….scary what choosy moms choose for the kids….

    • maria

      haha thats exactly why I’m here- peanut butter label!

    • JACK

      Actually, Jif is FULLY hydrogenated which makes it much safer to eat than any other brand.

      • Fooducate

        Not really. There are many PBs out there without any added oils. They are the better choice

        • Joe

          How can you have peanut butter without adding oil? It naturally seperates and without oil you cant have a constant consistency.

          • Dina Garcia RD LDN

            I buy peanut butter w/ the ingredients peanuts and salt. You are right it does separate. I leave it upside down on the counter for about a day and all the oil will float to the bottom (since it’s upside down). I turn it right side up, give it a stir then keep it in the fridge which prevents it from separating again. It is delicious

          • LB

            Some stores now offer fresh peanut butter you can blend yourself. It doesn’t separate if you keep it in the refrigerator and it stays soft enough to spread. Once you get used to it, you’ll never go back.

  • JustJay

    I just want to make a point that its not the trans-fat part of the equation that is bad its the fact that partially hydrogenated oil is made by chemist. When they bombard the fatty acid with more hydrogens it creates what we can transfatty acids. This new chemistry is recognized by the baody as a fat and goes into storage for later use. The problem, the body doesn’t know how to use it when needed. So once you ingest partially hydrogenated (any type of oil) its there in your fat cells for life!!! Your body will never be able to get rid of it, EVER! Got to love the FDA.

  • Soren

    why is it that Ghirardelli’s white chocolate frappe powder mix contains partially hydrogenated coconut oil yet claims on the nutrition facts to have no trans fat if partial hydrogenation leads to trans fat?

    • cheeeseburgers

      Food companies are allowed to “round down” if their product contains less than .5 g of trans fats. That’s why it’s so important to look at the ingredient list in addition to the nutrition facts.

      • L S

        It’s also a matter of serving size listed on the label. Tricky. The product can have lots of trans fat if they choose a tiny serving size/portion of the product that has less than one half gram in it to list on the package. (Vote to standardize portions on labels!)

        I’m here trying to figure out why 12 grams of Crisco (serving size) is supposed to have that magic zero trans fat if it’s full of hydrogenated and partially hydrogenated palm oil and soybean oil. (Cool history of Crisco on Wikipedia.)

  • sunny

    Thanks from South Korea.
    it was so difficult to understand that I was discouraged to my assignment, which is about trans fat, partially hydrogenatioed oil and.. those things.
    Your explanations are helpful.

  • Stacey Perry

    I just found it In my doughnut house green mountain coffee
    Sweet and creamy iced coffee. Arrrrhhhhhh hopefully I can return it.

  • Korios

    I recently e-mailed EFFET (the Greek FDA, sort off) on this, asking if or when they plan to come up with any proposals about trans fat usage, much like the FDA is planning to remove trans fats from their GRAS (Generally Regarded as Safe) list. I had no response and I do not think I’ll have one. Trans fats / partially hydrogenated fats are still very widespread in Greece, especially in the cheaper products..

  • Robert Hutchinson

    Coconut oil is very good for you and is pretty much a pure saturated fat

  • Elliot Dole

    For items that list an ingredient as hydrogenated oil – is it fair to assume they are using fully hydrogenated oil or is it a way to ambiguously incorporate trans fats (partially hydrogenated oil) into an ingredients list? Thanks.

  • Anthony

    What about non-hydrogenated oils, are they bad? If so, what are the risks?

  • Kevin

    If the label say “Hydrogenated soybean/cottonseed oil” without the word partially does that mean its fully hydrogenated?

  • Bala

    How I can reduce trans fat formation during hydrogenation reaction? I want to know the condition of reaction. tnx

  • Bala

    How I can reduce trans fat formation during hydrogenation reaction? I want to know the condition of reaction like temperature, pressure, catalyst dosing etc… advance thanks for suggestion..

  • PluviAL

    Great info, thanks for all the well informed comments too.