If you grew up in the 1980s or 90s, you were taught a simple equation: Fat = Bad. Carbs = Good.
Fat-free cookies. Low-fat yogurt. Skim milk. Margarine instead of butter. Egg white omelets.
That horrific fat free cheese.
SNACKWELLS.
We were told that if we just removed fat from our diets—especially saturated fat—we’d protect our hearts, stay skinny and live longer.
There was just one problem: It didn’t work.
Not only did the low-fat era fail to reduce heart disease rates, it coincided with an explosion of obesity, type 2 diabetes, and metabolic syndrome. The very conditions that increase cardiovascular risk.
So what went wrong? And more importantly, why are so many people still following advice from a failed nutritional experiment?
The Origins of Fat Phobia
The demonization of dietary fat didn’t come from robust scientific evidence. It came from a combination of questionable research, corporate influence, and well-meaning but ultimately misguided public health policy.
The diet-heart hypothesis, popularized by Ancel Keys in the 1950s-60s, suggested that dietary saturated fat raised cholesterol, which caused heart disease. There’s rumors – disputed – that Keys cherry-picked his data and ruthlessly pursued his agenda. Regardless of whether or not this is true, when it was published, there was some pushback.
Despite significant controversy and conflicting evidence, this hypothesis became nutritional gospel. Keys had connections to the White House, and during the time his research was published, US Congressmen were grappling with their own meteoric rise in heart attacks. The idea that the cholesterol we eat becomes the cholesterol in our arteries made sense at face value, and became ‘common knowledge’. By 1980, the U.S. government issued the first Dietary Goals for Americans, recommending that Americans reduce total fat intake and replace saturated fats with carbohydrates.
The food industry responded enthusiastically. As word got out and Americans began looking to avoid fats, fat was removed from thousands of products and replaced with sugar, refined carbohydrates, and in some cases, trans fats—which we now know are genuinely dangerous.
And, as a population, Americans complied. Between 1971 and 2000, the percentage of calories from fat in the American diet decreased, while carbohydrate intake increased significantly(2).
So if we followed the guidelines, why didn’t heart disease rates plummet?
What Actually Happened As We Cut Dietary Fat
Here’s the tragic outcome of the low fat era: Rates of obesity, type 2 diabetes, and metabolic syndrome increased dramatically in the United States and nations which followed suit.
When you remove fat from food, you have to replace it with something to maintain palatability and texture. That “something” was almost always sugar, refined flour, and other high-glycemic carbohydrates.
The consequences were metabolically catastrophic:
Increased insulin resistance: High-carbohydrate, low-fat diets increase postprandial insulin secretion and can contribute to insulin resistance over time. Insulin resistance is a primary driver of metabolic syndrome, which significantly increases cardiovascular risk. (3,4)
Elevated triglycerides: Low-fat, high-carbohydrate diets consistently raise triglyceride levels, particularly in individuals with insulin resistance or metabolic syndrome and when those carbohyrates come from refined sources such as flours and sugars. High triglycerides combined with low HDL is a powerful predictor of cardiovascular risk. (5)
Smaller, denser LDL particles: High refined-carbohydrate diets promote a shift toward smaller, denser LDL particles, which are more atherogenic than larger LDL particles. These are exactly the type of LDL particles that increase heart disease risk. (6)
Reduced HDL cholesterol: Low-fat diets tend to lower HDL (“good”) cholesterol levels. Since HDL helps remove cholesterol from arteries, lowering it is counterproductive for cardiovascular health. Additionally, a large meta‑analysis of 32 long‑term randomized controlled trials reported that HDL rose more on higher‑fat diets; low‑fat diets did not improve HDL to the same extent. (7) Another meta‑analysis of 20 RCTs in overweight/obese but metabolically healthy adults found significantly lower HDL on low‑fat versus high‑fat diets (−2.57 mg/dL; P<0.001), along with higher triglycerides. (8). That’s a double whammy if ever I saw one.
Increased inflammation: Diets high in refined carbohydrates and sugar increase systemic inflammation, a key driver of atherosclerosis.
In other words, the low-fat approach created the exact metabolic conditions that promote heart disease.
THE WEIGHT LOSS PARADOX
Here’s perhaps the most damning indictment of the low-fat approach: It didn’t even deliver on its promise of weight loss. Do you remember the adage “The Fat You Eat is the Fat You Wear”? It’s utter BS!
Despite Americans reducing their percentage of calories from fat and increasing low-fat food consumption between 1970-2000, obesity rates more than doubled during this same period. We were told that eating fat makes you fat—a simplistic, calorie-focused logic that ignored nuanced metabolic reality.
The truth is that fat is more satiating than carbohydrates. It triggers hormones that signal fullness, slows gastric emptying, and helps stabilize blood sugar. When you remove fat and replace it with rapidly digesting carbohydrates, you create a cycle of blood sugar spikes, insulin surges, and inevitable crashes that leave you hungry again within hours.
The low-fat era didn’t just fail to prevent heart disease—it failed to keep us thin, despite that being the primary selling point. Instead, the dietary recommendations of the low fat era created a population that was simultaneously overfed and undernourished, caught in a cycle of restriction, hunger, and weight regain.
The Fats We Actually Need
Not all fats are created equal—but that doesn’t mean we should avoid fat entirely. In fact, certain fats are essential for cardiovascular health.
Omega-3 Fatty Acids (EPA and DHA)
I’ve already covered the robust evidence for omega-3s here, here and here. Wild-caught fatty fish like salmon, sardines, mackerel, and anchovies provide anti-inflammatory omega-3s that:
- Reduce triglycerides
- Lower inflammation (as measured by hs-CRP)
- Improve endothelial function
- Stabilize heart rhythm
- Reduce cardiovascular mortality
- Support mental health
- Reduce the risk of brain disease
The American Heart Association recommends eating fatty fish at least twice per week for cardiovascular health. I recommend 3-4 times per week if you’re serious about it, or if you are also concerned about brain health.
Monounsaturated Fats
Found in olive oil, avocados, nuts, and certain seeds, monounsaturated fats have consistently demonstrated cardiovascular benefits.
The Mediterranean diet, which is rich in monounsaturated fats from olive oil, is the most robustly researched dietary pattern. It has been shown to reduce cardiovascular events and mortality despite being moderate in fat, mostly from olive oil. Extra virgin olive oil contains polyphenols and other bioactive compounds that reduce inflammation and improve endothelial function. It is believed that diets rich in olive oil are cardioprotective for this reason.
Saturated Fat: More Nuanced Than You Think
This is where the conversation gets interesting, and controversial.
For decades, saturated fat has been vilified as the primary dietary demon in heart disease. But more recent research has complicated this narrative significantly.
Meta-analyses examining the relationship between saturated fat intake and cardiovascular disease have found no significant association (9,10). Some studies suggest that the source and context of saturated fat matters more than total intake—saturated fat from whole food sources like dairy may have neutral or even protective effects (11, 12).
This doesn’t mean you should start eating pounds of bacon daily. (Sorry!) It means the blanket demonization of all saturated fat was overly simplistic.
What matters more:
- What you’re eating it with: Saturated fat consumed alongside high amounts of refined carbohydrates and sugar creates a different metabolic response than saturated fat consumed in the context of whole foods and vegetables
- Your individual metabolic health: People with insulin resistance or metabolic syndrome may respond differently to saturated fat than metabolically healthy individuals
The point isn’t that all saturated fat is healthy. The point is that context matters, and treating all saturated fat as equally harmful was scientifically unsound.
The Fats to Actually Avoid
While we’re rehabilitating the reputation of dietary fat, let’s be clear about which fats genuinely harm cardiovascular health:
Trans fats: Industrial trans fats (partially hydrogenated oils) significantly increase cardiovascular disease risk and have been banned in many countries. These were ironically promoted as heart-healthy alternatives to butter during the low-fat era.
Oxidized fats: Fats that have been damaged through excessive heat, light, or processing can form harmful compounds that contribute to oxidative stress and inflammation. Repeatedly using the same oil for frying is a problem, and for this reason it’s best to avoid fried foods from restaurants, as they may not change the oil in the fryer as often as is needed.
What Your Heart Actually Needs
Your cardiovascular system doesn’t need you to avoid fat. It needs you to:
1. Prioritize anti-inflammatory fats
- Wild-caught fatty fish at least 3 times per week
- Extra virgin olive oil as your primary cooking and finishing oil
- Avocados, nuts, and seeds in moderation
- Quality sources of saturated fat (grass-fed dairy, pasture-raised eggs) in the context of a nutrient-dense diet
2. Eliminate genuinely harmful fats
- All trans fats (check labels for “partially hydrogenated oils”)
- Avoid repeatedly heated oils
3. Address the real drivers of cardiovascular disease
- Chronic inflammation (diet, stress, sleep, movement)
- Insulin resistance and blood sugar dysregulation
- Oxidative stress (smoking, pollution, alcohol use)
- Metabolic syndrome
- Nutrient deficiencies (especially magnesium, omega-3 fats, and folate)
4. Focus on food quality, not just macronutrient ratios A piece of wild-caught salmon cooked in olive oil with vegetables is metabolically different from a low-fat muffin, even if they contain similar calories. Quality matters.
The Cultural Damage of Fat Phobia
Beyond the metabolic consequences, the low-fat era created lasting psychological and cultural damage around food.
It taught us to:
- Fear satisfying, nutrient-dense whole foods
- Prioritize “fat-free” processed products over whole foods
- Believe that hunger and deprivation are necessary for health
- Disconnect from our body’s natural satiety signals (fat is satiating; sugar is not)
- View food through a reductive lens of “good” and “bad” rather than understanding nutritional complexity
Many people are still operating under these beliefs, choosing low-fat yogurt loaded with sugar over full-fat Greek yogurt, or avoiding egg yolks in favor of refined carbohydrate-heavy breakfasts.
The irony? Some people find that higher-fat, lower-carbohydrate dietary patterns often result in better adherence, greater satiety, and improved metabolic markers compared to low-fat approaches. Clinically, I see a strong trend toward satiety when protein is increased, with some being quite satisfied on lower carbs and others needing a more moderate carbohydrate approach. The point here is that going low fat can sometimes exacerbate hunger and cravings, counter to what we were told we needed to do to manage weight and health.
Do I Need to Go Keto or Very Low Carb?
Absolutely not. In the low-fat 80s and 90s, it was recommended we get 60-70% of our calories from carbohydrates. The answer is not to swing in the other direction. “Low carb” research comprises diets that are as low as 10% carbs and as high as 40% carbs, so you see the range of what ‘low carb’ means is quite vast! Finding out how many carbohydrates are best for you body can take some time, and using a nutritional professional to help you out can be an efficient and effective way to do so. A competent nutrition professional will take your age, health history, activity level, and personal response to hunger and cravings into consideration when making recommendations. Be wary of anyone who aims for a singular, narrow dietary answer to your health problems!
Moving Forward: A More Intelligent Approach
We can’t change the dogma from our past, but we can choose a smarter path forward.
Instead of asking: “Is this food high in fat?”
Ask Yourself:
- What kind of fat does this contain?
- Is this a whole food or highly processed?
- What will this do to my blood sugar and insulin?
- Does this reduce or promote inflammation?
- Will this satisfy me or leave me hungry in an hour?
Practical shifts:
- Replace fat-free dairy with full-fat versions (no added sugar)
- Cook with olive oil, avocado oil, or grass-fed butter.
- Choose fatty fish over lean protein several times per week
- Add avocado, nuts, or seeds to meals for satiety and nutrient absorption
- Stop fearing egg yolks—they’re among the most nutrient-dense foods available and contain Vitamin E and choline – which is cardioprotective!!
- Read labels: “low-fat” often means “high-sugar”
The Bottom Line
The low-fat diet experiment failed because the hypothesis was wrong from the start.
Cardiovascular health is complex, metabolically driven, and deeply connected to inflammation, insulin sensitivity, and overall metabolic function. While it seemed logical at the time, it’s beyond evident that fats are not the enemy.
They’re essential—for hormone production, cellular function, nutrient absorption, satiety, and yes, cardiovascular health.
The real threat to heart health is the chronic inflammation, insulin resistance, and metabolic dysfunction that the low-fat era helped create.
Now who wants to tuck into an avocado with me?
Resources:
- Newport MT, Dayrit FM. The Lipid-Heart Hypothesis and the Keys Equation Defined the Dietary Guidelines but Ignored the Impact of Trans-Fat and High Linoleic Acid Consumption. Nutrients. 2024 May 11;16(10):1447. doi: 10.3390/nu16101447. PMID: 38794685; PMCID: PMC11123895.
- (2004). Trends in intake of energy and macronutrients–United States, 1971-2000.. MMWR. Morbidity and mortality weekly report, 53 4, 80-2 . https://doi.org/10.1001/jama.291.10.1193.
- Papakonstantinou, E., Oikonomou, C., Nychas, G., & Dimitriadis, G. (2022). Effects of Diet, Lifestyle, Chrononutrition and Alternative Dietary Interventions on Postprandial Glycemia and Insulin Resistance. Nutrients, 14. https://doi.org/10.3390/nu14040823.
- Chang, L., Vethakkan, S., Nesaretnam, K., Sanders, T., & Teng, K. (2016). Adverse effects on insulin secretion of replacing saturated fat with refined carbohydrate but not with monounsaturated fat: A randomized controlled trial in centrally obese subjects.. Journal of clinical lipidology, 10 6, 1431-1441.e1 . https://doi.org/10.1016/j.jacl.2016.09.006.
- Willems, A., Jong, M., Van Beek, A., Nederhof, E., & Van Dijk, G. (2020). Effects of macronutrient intake in obesity: a meta-analysis of low-carbohydrate and low-fat diets on markers of the metabolic syndrome. Nutrition Reviews, 79, 429 – 444. https://doi.org/10.1093/nutrit/nuaa044.
- Gerber, P., & Berneis, K. (2012). Regulation of low-density lipoprotein subfractions by carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care, 15, 381–385. https://doi.org/10.1097/mco.0b013e3283545a6d.
- Schwingshackl, L., & Hoffmann, G. (2013). Comparison of effects of long-term low-fat vs high-fat diets on blood lipid levels in overweight or obese patients: a systematic review and meta-analysis.. Journal of the Academy of Nutrition and Dietetics, 113 12, 1640-61 . https://doi.org/10.1016/j.jand.2013.07.010.
- Lu, M., Wan, Y., Yang, B., Huggins, C., & Li, D. (2017). Effects of low-fat compared with high-fat diet on cardiometabolic indicators in people with overweight and obesity without overt metabolic disturbance: a systematic review and meta-analysis of randomised controlled trials.. The British journal of nutrition, 119 1, 96-108 . https://doi.org/10.1017/s0007114517002902.
- Siri-Tarino, P., Sun, Q., Hu, F., & Krauss, R. (2010). Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease.. The American journal of clinical nutrition, 91 3, 535-46 . https://doi.org/10.3945/ajcn.2009.27725.
- Zhu, Y., Bo, Y., & Liu, Y. (2019). Dietary total fat, fatty acids intake, and risk of cardiovascular disease: a dose-response meta-analysis of cohort studies. Lipids in Health and Disease, 18. https://doi.org/10.1186/s12944-019-1035-2.
- De Oliveira Otto, M., Mozaffarian, D., Kromhout, D., Bertoni, A., Sibley, C., Jacobs, D., & Nettleton, J. (2012). Dietary intake of saturated fat by food source and incident cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis.. The American journal of clinical nutrition, 96 2, 397-404 . https://doi.org/10.3945/ajcn.112.037770.
- Astrup, A., Magkos, F., Bier, D., Brenna, J., De Oliveira Otto, M., Hill, J., King, J., Mente, A., Ordovás, J., Volek, J., Yusuf, S., & Krauss, R. (2020). Saturated Fats and Health: A Reassessment and Proposal for Food-based Recommendations: JACC State-of -the-Art Review.. Journal of the American College of Cardiology. https://doi.org/10.1016/j.jacc.2020.05.077.
