Good fat, bad fat

Dr. Abigail Vermeesch, BCDHH, CNHP, CHS, BS, MS Clinical Nutrition Nutrition & Lifestyle 8 min read Medically reviewed July 2026

Fat is essential for the body — but not all fats are created equal. After decades of low-fat messaging, it’s time to end the fear of fat, understand which fats truly help or harm, and learn how to use them well.

Key takeaways

Fat is essential — for the brain and nerves, cell membranes, hormones, and absorbing vitamins A, D, E, and K.

Artificial trans and partially hydrogenated fats are the clearest harm — avoid them entirely.

Modern diets skew heavily toward omega-6 over omega-3, which can drive chronic inflammation — balance matters.

Choose minimally processed fats — and match the fat to the heat, since a good fat can turn bad when overheated.

In this article

— Why fat is so important

— Types of fats

— How oils are extracted & refined

— Good fats vs. bad fats

— The omega-6 factor

— Choosing fats for cooking

Fat is essential for many functions in the body — but not all fats are created equal. For over 50 years we were fed a lot of misinformation about fat, and many people followed low-fat diets while a great deal of money was made on products labeled “fat-free.” The tide has turned, and dietary fat is being welcomed back. (One honest caveat: the science on saturated fat specifically is still debated — the clearest consensus is that whole-food fats belong in the diet and that artificial trans fats are the ones to avoid.) It’s time to end the fear of fat.

Common myths about fat: “Fat will make you fat.” · “Fat will clog your arteries.” · “Eating fat will raise your cholesterol.” The reality is more nuanced — and more hopeful.

Why fat is so important

Brain and nerve tissue. At about 60% fat, the brain is the fattiest organ in the body. Fat is the main insulation of nerves and a large part of the myelin sheath — essential for a properly functioning nervous system.

Cell membranes. Cell and sub-cellular membranes are largely a phospholipid bilayer — fat combined with phosphorus — that lets nutrients, hormones, and neurotransmitters be used properly and lets cell waste leave. Poor membrane function means the whole body functions poorly.

Hormones. After the brain, the organs most hungry for fat are the endocrine glands. All steroid hormones are built from cholesterol — a fat.

Vitamin absorption. Dietary fat is needed to absorb and use the fat-soluble vitamins A, D, E, and K — and it’s needed for calcium absorption too.

Fuel. Fat holds more energy per gram than carbohydrate or protein and provides long-burning, stable energy that low-fat diets lack.

Essential fatty acids. Fat supplies the EFAs your body can’t make on its own — essential for healthy cells, tissues, nerves, and hormones.⁴

Types of fats

Saturated fats have fatty-acid chains made of mostly or all single bonds. Most animal fats are saturated; the best sources are full-fat dairy, fatty meats, coconut oil, and palm oil. Because they have a higher melting and smoke point, they’re more stable for higher-temperature cooking without oxidizing (which creates damaging free radicals), and they give cells some of the rigidity they need. Their role in heart disease is genuinely debated, so quantity and your overall diet matter.

Unsaturated fats are liquid at room temperature and give cell membranes the fluidity they need. They come in two kinds:

Monounsaturated (one double bond)

Found in olive, safflower, peanut, and sesame oils, plus avocados, nuts, and seeds. Benefits include improved cardiovascular health, lower BMI, better membrane function, and reduced inflammation.

Polyunsaturated (two or more double bonds)

Found in fatty fish (salmon, mackerel, herring, tuna, trout) and in walnuts, sunflower and flax seeds, and several seed oils. Benefits include supporting membrane fluidity, modulating insulin receptors and glucose transporters, and reducing inflammation. They’re the least heat-stable, so they’re best used cold.

Studies of the Mediterranean diet — which emphasizes mono- and polyunsaturated fats — show lower fasting glucose, triglycerides, and other markers of metabolic syndrome.¹

How oils are extracted & refined

How an oil is extracted and refined largely determines its quality:

Cold-pressed / mechanically extracted. Nuts or seeds are ground and pressed with little or no heat. Higher quality, though it yields less oil.

Heat-extracted. Outside heat is applied to release more oil — higher yield, but some argue lower quality.

Chemically / solvent extracted. Ground seeds are washed with a petroleum distillate (usually hexane), then heated to distill off the solvent. Highest yield, lowest quality — most industrial vegetable oils are made this way, mainly for cost.

Naturally refined vs. unrefined. Naturally refined oils are filtered without chemicals and tolerate higher heat; unrefined oils keep more delicate nutrients and antioxidants and are best at lower temperatures, since overheating creates free radicals.

Good fats vs. bad fats

In general, good fats come to us naturally and minimally processed; bad fats are refined and chemically extracted. Two things deserve special attention: trans fats, and the omega-6 balance.

Hydrogenated & trans fats = always avoid. This is the one area of fat research that’s crystal clear. Made by “partial hydrogenation” into an unnatural fat that’s solid at room temperature, trans fats are cheap and common in fried foods and baked goods — look for “partially hydrogenated vegetable oil,” “shortening,” and margarine. They cause cellular inflammation and dysfunction, and have been linked to coronary heart disease, sudden cardiac death, and diabetes — even at low intakes.² Read labels and skip them entirely.

Refined, chemically extracted oils to limit or avoid include canola, cottonseed, corn, margarine, and vegetable shortening — whether or not they’re labeled organic.

The omega-6 factor

We need both omega-3 and omega-6 essential fatty acids, since the body can’t make them. But over time our omega-6 intake has risen dramatically relative to omega-3, which can promote chronic inflammation.³ Depending on how many omega-3s you eat, you may want to limit plant oils high in omega-6:

Soybean oil

Canola oil

Corn oil

Cottonseed oil

Sunflower oil

Peanut oil

Sesame oil

Rice bran oil

Balance the scale from the other side, too, by eating more omega-3s — fatty fish, walnuts, and ground flax. (For the bigger picture, see chronic inflammation and anti-inflammatories.)

Choosing fats for cooking

We love animal and plant fats that come to us naturally and minimally processed — high-quality cold-pressed olive oil and avocado oil, plus lard, ghee, tallow, and coconut oil. But a good fat can turn into a bad fat if it’s overheated. Two things decide how a fat handles heat: its percentage of polyunsaturated fat (the least stable kind) and its smoke point. As a general guide:

Best for higher-heat cooking (stable, low PUFA)

Avocado oil, ghee, tallow, coconut oil, and naturally refined olive oil.

Best for low heat & finishing

Extra-virgin olive oil and butter — great for light sautéing, dressings, and drizzling.

Keep off the heat (delicate, high PUFA)

Flaxseed oil, walnut oil, and other unrefined high-polyunsaturated oils — use cold only.

Avoid. Margarine, shortening, and refined industrial seed oils (canola, corn, cottonseed, soybean).

A general guide based on smoke point and the balance of saturated, monounsaturated, and polyunsaturated fats; exact smoke points vary by refinement and brand.

Do your research and choose fats that are organic, minimally processed, and that encourage a good balance of omega-3s and omega-6s — and be smart about which fats you cook with and which stay out of the sauté pan. In doing so, you’ll support better brain and cellular health, better vitamin absorption, more balanced hormones, less inflammation, and a healthier weight. Welcome fat back into your diet — the right ones, used the right way.

Common questions

Is saturated fat bad for you?

The old “artery-clogging” view has been challenged, and the evidence on saturated fat and heart disease is genuinely debated. What’s clear is that whole-food saturated fats (full-fat dairy, quality meats, coconut) are stable for cooking, while artificial trans fats are harmful. Your ideal intake depends on your overall diet and health picture.

What are the worst fats to eat?

Artificial trans fats and partially hydrogenated oils — linked to coronary heart disease, sudden cardiac death, and diabetes even at low intakes. Avoid “partially hydrogenated oil,” shortening, and margarine, along with heavily refined, solvent-extracted vegetable oils.

What is the omega-6 problem?

We need both omega-3 and omega-6, but modern diets skew heavily toward omega-6, which can promote chronic inflammation. Limiting high-omega-6 industrial oils (soybean, corn, cottonseed, sunflower) and eating more omega-3s (fatty fish, walnuts, flax) helps restore balance.

Which fats are best for cooking?

For higher heat, choose stable, lower-polyunsaturated fats with higher smoke points — avocado oil, ghee, tallow, coconut oil. Use extra-virgin olive oil for lower heat and finishing. Keep delicate oils like flaxseed and walnut off the heat, and avoid refined industrial seed oils.

References (4) ▾

Kastorini CM, Milionis HJ, Esposito K, Giugliano D, Goudevenos JA, Panagiotakos DB. The effect of Mediterranean diet on metabolic syndrome and its components: a meta-analysis of 50 studies and 534,906 individuals. J Am Coll Cardiol. 2011;57(11):1299-1313. https://pubmed.ncbi.nlm.nih.gov/21392646/
Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. N Engl J Med. 2006;354(15):1601-1613. https://pubmed.ncbi.nlm.nih.gov/16611951/
Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed Pharmacother. 2002;56(8):365-379. https://pubmed.ncbi.nlm.nih.gov/12442909/
Jones DS, ed. (Bennett P, Bland JS, Galland L, et al.). Textbook of Functional Medicine. Gig Harbor, WA: Institute for Functional Medicine; 2010.

This article is educational and is not medical advice, diagnosis, or treatment. Dietary fat needs vary with individual health conditions — discuss significant changes with a qualified practitioner.

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