Dietary Fats: The Good, the Bad, and the Myths (2025)

▲By Dr. Hannah Cole, Nutrition Science Reviewer · Published 2026-07-19 · Updated 2026-07-31

✍️ Written by Dr. Hannah Cole, PhD, RD — Nutrition Science Reviewer.
✅ Medically reviewed by Peter Vance, MS Nutrition — Sports & Performance Writer, for accuracy against current nutrition guidance.

Educational information, not medical advice. This article is for general information only and is not a substitute for professional medical or dietary advice. Talk to your doctor or a registered dietitian before changing your diet, starting supplements, or fasting — especially if you are pregnant or nursing, take medication, or have a health condition.

Olive oil, avocado, salmon and nuts representing healthy unsaturated fats

Fat is essential, not optional

The low-fat era of the 1990s got it wrong. Fat is vital — it builds cell membranes, makes hormones, and helps absorb vitamins A, D, E, and K. The Harvard T.H. Chan — Fats and Cholesterol reframes the question: it's not how much fat but which kind.

A simple hierarchy of fats

Best — unsaturated (mono & poly): olive oil, avocado, nuts, seeds, fatty fish. Protective for the heart.
Okay in moderation — saturated: butter, red meat, coconut oil. Not the poison once claimed, but best limited.
Worst — trans fats: partially hydrogenated oils in some processed foods. Avoid entirely; they raise bad cholesterol and lower good.

Why omega-3s get special attention

The NIH ODS — Omega-3 Fatty Acids Fact Sheet for Consumers summarizes evidence that omega-3 fats (EPA and DHA from fatty fish, ALA from flax and walnuts) support heart and brain health. Two servings of fatty fish a week is a common, food-first target.

The 'low-fat' trap

Low-fat processed foods often replace fat with sugar and refined starch, making them no healthier. Whole foods with natural fats — nuts, olive oil, fish — beat engineered low-fat snacks, as the Harvard T.H. Chan — Nuts for the Heart illustrates.

Putting it on your plate

Cook with olive oil, snack on a handful of nuts, add avocado, eat fish twice a week, and check ingredient lists for 'partially hydrogenated' anything. That covers 90% of good fat strategy.

The fats that help and the fats that harm

Not all fat is equal. Unsaturated fats — from olive oil, nuts, seeds, avocado, and fish — support heart health and should make up most of your fat intake. Saturated fat, found in fatty meat and full-fat dairy, is fine in moderation. Artificial trans fats, still lurking in some fried and packaged foods, raise bad cholesterol and should be avoided entirely. The Harvard T.H. Chan — Fats and Cholesterol lays out the evidence clearly.

Why omega-3s deserve special attention

Omega-3 fatty acids — abundant in salmon, sardines, walnuts, and flaxseed — are linked to heart and brain health and reduced inflammation. Many people fall short. The NIH ODS — Omega-3 Fatty Acids Fact Sheet for Consumers outlines sources and sensible intakes; two servings of oily fish per week is a common, food-first recommendation before considering a supplement.

The essentials

Prioritize unsaturated fats from olive oil, nuts, seeds, avocado, and fish.
Keep saturated fat moderate and avoid artificial trans fats entirely.
Omega-3s support heart and brain health; many people fall short.
Two servings of oily fish weekly is a solid food-first target.
Fat is calorie-dense — quality and portion both matter.

Nutrition questions

Is saturated fat bad for you?

It's best limited but not the sole villain once believed. Replacing saturated fat with unsaturated fat (not refined carbs) is linked to better heart outcomes. Trans fats are the ones to avoid entirely.

What are the healthiest fats?

Unsaturated fats from olive oil, avocado, nuts, seeds, and fatty fish. Omega-3 fats from fish, flax, and walnuts get special attention for heart and brain health.

Are low-fat foods healthier?

Not necessarily. Many processed low-fat products replace fat with sugar and refined starch. Whole foods with natural fats are usually the better choice.

Is dietary fat what makes you fat?

Not directly. Fat is calorie-dense, so portions matter, but eating healthy fats within your calorie needs supports health and satiety. Overall calorie balance and food quality drive weight, not fat alone.

References

This guide is reviewed against current guidance from the sources above. Nutrition science evolves; always confirm with a qualified healthcare professional for your individual needs.

Medical disclaimer. The content above reflects general nutrition science and may not apply to your personal circumstances. It does not diagnose, treat, or cure any condition. Individual needs vary with age, health status, medications, and activity. Always seek the advice of your physician or a registered dietitian with any questions about a medical condition or before making dietary changes.