Is Dietary Fat Really Bad for You?
Written by Michelle Oliveira — Founder of Fit by Mi and co-owner of Proven Science Nutrition. Ph.D., NASM-certified nutrition coach and personal trainer, and two-time Ms. Indiana Bikini champion. Science First. Results Always.
I can't tell you how many times a new client has sat down with me, looked at her meal plan, seen avocado, whole eggs, or a spoonful of olive oil on it, and asked — half nervous, half guilty — "Wait… am I allowed to eat that? Aren't fats bad for you?"
I get it. If you grew up in the '90s or 2000s, you were raised to believe fat was the enemy. Fat-free cookies, skim everything, "low-fat" labels slapped on boxes of pure sugar. Then, almost overnight, keto flipped the script and suddenly fat was a superfood and carbs were the villain. No wonder everyone's confused.
So let's clear this up, coach to athlete. Dietary fat is not the enemy. It never was. Like carbohydrates, fat has spent decades on trial for a crime it didn't commit — and as a nutrition coach, watching women under-eat this essential nutrient out of fear is one of the most common (and most fixable) mistakes I see. Let's talk about what fat actually does, where the fear came from, and how to use it to support your goals instead of sabotaging them.
Where the fear of fat came from
The anti-fat panic wasn't random. Decades ago, public health messaging zeroed in on dietary fat as the main driver of heart disease and obesity, and the food industry ran with it. "Low-fat" and "fat-free" became health halos — even when the product was loaded with sugar to make up for the missing flavor.
Two things made the fear stick. First, the name. "Fat" is the same word we use for body fat, so it feels logical that eating fat makes you fat. Second, the math: fat contains 9 calories per gram, more than double the 4 calories per gram in carbs and protein. More calories per bite got wrongly translated into "fat is uniquely fattening."
Both of those are traps. Let me walk you through why.
What dietary fat actually does for your body
Fat isn't just a calorie source you tolerate — it's a nutrient your body genuinely needs. Here's what it's doing behind the scenes every day:
It runs your hormones. Fat is the raw material your body uses to produce steroid hormones, including your sex hormones. This matters enormously for women, for energy, mood, recovery, and menstrual health. Skimp too hard and your body notices.
It unlocks key vitamins. Vitamins A, D, E, and K are fat-soluble, which means your body literally cannot absorb them without dietary fat present.[1] That "healthy" fat-free salad with no dressing? You're absorbing far fewer of the nutrients in it than you would with a drizzle of olive oil.
It keeps you full and satisfied. Fat slows digestion and helps you feel satiated, which — ironically — can make it easier, not harder, to stay on track with your nutrition.
It builds and protects. Every cell membrane in your body contains fat. Your brain is roughly 60% fat. Fat cushions your organs and provides steady, long-lasting energy.
This is why the official Acceptable Macronutrient Distribution Range recommends that adults get 20–35% of daily calories from fat — not zero.[1] Fat isn't optional. It's foundational.
The "fat makes you fat" myth
Let's tackle the big one head-on, because this is the belief that keeps women scared of their own food.
Eating fat does not automatically make you gain body fat. Body fat is gained when you consistently eat more calories than you burn — full stop. That's true whether the surplus comes from fat, carbs, or protein. Dietary fat has no magical power to add to your waistline that the other macros don't.
Now, here's the honest nuance I give my clients: because fat is calorie-dense at 9 calories per gram, it's easy to overeat if you're not paying attention. A handful of nuts here, extra oil there, and the calories add up fast. But that's a portion-awareness issue, not a reason to fear the nutrient itself. The fat isn't the problem — the total is. Whole-food fats, eaten with intention, are one of the most nourishing things on your plate.
Not all fats are created equal
Here's where it gets genuinely important, because "fat" isn't one thing. The type of fat matters far more than the total amount for your long-term health.
Unsaturated fats (your everyday heroes). These are the monounsaturated and polyunsaturated fats found in olive oil, avocados, nuts, seeds, and fatty fish. The evidence here is strong and reassuring. A major American Heart Association advisory found that replacing saturated fat with polyunsaturated fat reduced cardiovascular disease by about 30% — a benefit comparable to statin medication.[2] Notably, that same review found that replacing saturated fat with refined carbohydrates (hello, fat-free snacks) did not reduce heart disease at all.[2] Swapping fat for sugar was never the answer.
Omega-3s (worth prioritizing). A specific type of polyunsaturated fat found in fatty fish like salmon and sardines, omega-3s support heart health and help manage inflammation. Most people don't get enough.
Saturated fats (fine in moderation). Found in red meat, butter, and coconut oil, these don't need to be eliminated, but most health authorities suggest keeping them moderate and favoring unsaturated sources where you can.[2]
Trans fats (the actual villain). If any fat has earned its bad reputation, it's industrially produced trans fats from partially hydrogenated oils. These raise your "bad" LDL cholesterol, lower your "good" HDL, increase inflammation, and are linked to coronary heart disease and diabetes.[3] This is the one category worth genuinely avoiding — check labels for "partially hydrogenated oil."
See the pattern? The problem was never "fat." It was lumping heart-protective olive oil and avocado into the same category as trans-fat-laden processed junk.
Why eating too little fat backfires
This is the part I most want the women I coach to hear, because the low-fat instinct runs deep — especially during a fat-loss phase or competition prep, when the temptation is to strip fat down to almost nothing.
Please don't. Cutting fat too low can work directly against you, and the hormone connection is real. A 2021 systematic review and meta-analysis found that low-fat diets significantly decreased testosterone levels in men.[4] Testosterone matters for women too — in smaller amounts, it contributes to libido, muscle, and drive — and more broadly, your entire sex-hormone system depends on adequate dietary fat to function.[4]
In practice, when a client comes to me exhausted, moody, not recovering, sleeping poorly, or with a menstrual cycle that's gone haywire, chronically under-eating fat is one of the first things I look at. You cannot starve your hormones and expect your body to perform, recover, and look its best. Fat is not the thing standing between you and your goals. Very often, too little of it is.
How much fat, and what kind?
Let me make this practical, the way I would with a client:
Aim for the range. Roughly 20–35% of your daily calories from fat is a well-supported target for most people.[1] If you're active, don't be afraid of the middle of that range.
Build from whole foods. Make your fats work double duty by getting them from nutrient-dense sources: avocado, nuts, seeds, extra-virgin olive oil, fatty fish, whole eggs. These bring vitamins, minerals, and fiber along for the ride.
Prioritize unsaturated and omega-3s. Favor olive oil and fish over heavily processed options, and aim to include fatty fish a couple of times a week.
Actually avoid trans fats. Scan ingredient lists for "partially hydrogenated oil" and leave those on the shelf.[3]
Mind portions, not existence. Because fat is calorie-dense, measure it while you're learning — a tablespoon of oil and a "glug" of oil are very different. But measure it so you can include it confidently, not eliminate it.
The coach's bottom line
Fat is not the enemy. Carbs aren't either. When you zoom out, the same truth applies to both: there are no villain macronutrients, only quality, quantity, and context. Dietary fat fuels your hormones, feeds your brain, unlocks your vitamins, keeps you satisfied, and protects your heart when you choose the right kinds. Fearing it — or slashing it to nothing — is one of the fastest ways to feel worse and stall your progress.
So yes: eat the avocado. Drizzle the olive oil. Enjoy the whole eggs and the salmon. Your body has been asking for them all along.
Want a plan built around you?
Everything here is the general science — but macros, portions, and the right fat targets for your body, your training, and your goals are deeply individual. That's exactly what I do. At Fit by Mi, I build personalized, evidence-based nutrition and training plans (no fads, no fear-mongering, no food guilt) for women who are done guessing and ready for real results. If this article gave you permission to stop fearing your food, imagine what a plan made just for you could do.
Fuel smart. Trust the science. And be kind to your body.
Science first. Results always.
Written by Michelle Oliveira, founder of Fit by Mi (fitbymi.net) and co-owner of Proven Science Nutrition. Michelle holds a Ph.D. and NASM certifications in nutrition coaching and personal training, is a two-time Ms. Indiana Bikini champion, and coaches women in English, Spanish, and Portuguese.
*This article is for educational purposes and is not a substitute for individualized medical or nutritional advice. Consult a qualified healthcare professional before making significant changes to your diet, especially if you have a pre-existing medical condition.
References
U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025. 9th Edition. (Acceptable Macronutrient Distribution Range for fat: 20–35% of total calories; dietary fat is required for absorption of the fat-soluble vitamins A, D, E, and K.)
Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association. Circulation. 2017;136(3):e1–e23. doi:10.1161/CIR.0000000000000510
Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC. Trans fatty acids and cardiovascular disease. New England Journal of Medicine. 2006;354(15):1601–1613. doi:10.1056/NEJMra054035
Whittaker J, Wu K. Low-fat diets and testosterone in men: systematic review and meta-analysis of intervention studies. Journal of Steroid Biochemistry and Molecular Biology. 2021;210:105878. doi:10.1016/j.jsbmb.2021.105878
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