Dietary fat has been feared, defended, then feared again, and the confusion comes from reading one study at a time. Here is where the evidence sits. Saturated fat on its own is closer to neutral for heart disease than its reputation, and cutting fat did not make people leaner. What takes the fat's place matters more than the amount: swap saturated fat for the polyunsaturated fat in vegetable oils, nuts and seafood and heart attacks fall about a fifth; swap it for refined starch and sugar and they do not.
Two points hold firm. Industrial trans fat clearly raises heart disease risk, and saturated fat raises LDL cholesterol more than any other fat. Whole-food fats like butter and eggs land near ordinary, and the strongest signal across all of it is toward less processed food, whatever the number on the label.
Findings & Outcomes
What This Is
For fifty years the advice on dietary fat has swung between two slogans, and both are too simple. The first held that fat, and saturated fat above all, makes people sick and fat; supermarkets, menus and dietary guidelines were rebuilt around it. The second holds that fat is fine and sugar is the only enemy. The advice keeps flipping because each cohort, trial and headline gets read on its own, true inside its own frame and misleading as a full account.
Four questions run through the arguments about fat, and the evidence answers them separately: does saturated fat on its own cause heart disease, does eating fat make you fat, which fat clearly harms, and what should take the place of the fat you cut. The rest of this page works through them one at a time, and each finding is graded below at its true strength.
How Fat Became The Villain
The low-fat era grew from a plausible chain of reasoning promoted with more certainty than the trials could carry: saturated fat raises cholesterol, and cholesterol relates to heart disease. As that advice became policy in the 1970s and 1980s, food changed to match it. Fat came out of packaged products and sugar and refined starch went in to keep them palatable. Fat intake fell across those decades while sugar consumption and obesity rose. Coincidence in time does not establish cause, but it is a poor result for the theory.
The record also shows industry money shaping the question. A historical analysis of internal industry documents found that in the 1960s a sugar trade group paid Harvard researchers to publish a review that played down sugar's role in heart disease and pointed attention toward fat and cholesterol, without disclosing the funding (Kearns et al., 2016, JAMA Intern Med). That one episode did not create the low-fat consensus, but it shows the sugar industry helping decide which nutrient took the blame while the blame was still open. Some of the older literature was not neutral. The how industry shapes science page follows how funding has bent research questions before.
What The Saturated-Fat Trials Actually Show
Pooling the large prospective studies weakened the simple story. A meta-analysis of 21 cohorts covering almost 350,000 people found no significant association between saturated fat intake and coronary heart disease, stroke, or cardiovascular disease overall (Siri-Tarino et al., 2010). That meta-analysis was funded by the National Dairy Council, an industry tie that earns the same skepticism as the sugar-industry funding behind the low-fat literature, and the finding held up in independent work.
Two later studies pointed the same way. A systematic review in the BMJ reached the same conclusion for saturated fat and death, heart disease and type 2 diabetes, while flagging trans fat as harmful (de Souza et al., 2015). The PURE study, following 135,335 people across 18 countries, found higher total fat intake tracked with lower mortality and higher carbohydrate intake with higher mortality (Dehghan et al., 2017).
None of this means saturated fat is inert. It raises LDL cholesterol, more than any other fat does, established across 60 controlled feeding trials (Mensink et al., 2003). LDL is a biomarker standing in for the outcome, and the same food that raises LDL also raises HDL, so its effect on heart attacks depends on what replaces it. That is why the cohort outcomes and the cholesterol number can point in different directions.
What Replaces The Fat Matters
The strongest finding in this literature is about substitution. In randomized trials where polyunsaturated fat from vegetable oils, nuts and seafood took the place of saturated fat, coronary events fell about 19% in the pooled trials, and cardiovascular events fell 21% in the Cochrane review, with the benefit concentrated where polyunsaturated fat did the replacing (Mozaffarian et al., 2010; Hooper et al., 2020).
Swap the same saturated fat for carbohydrate and the benefit disappears. A pooled analysis of 11 cohorts found that replacing saturated fat with polyunsaturated fat lowered coronary risk, while replacing it with carbohydrate nudged risk slightly upward (Jakobsen et al., 2009). This is the swap the low-fat era encouraged, fat out and refined starch and sugar in, and it was the wrong one. Trading saturated fat for whole-food unsaturated fat lowers heart disease; trading it for refined carbohydrate does not. The Mediterranean diet, built on olive oil, nuts, fish and vegetables, is that same swap turned into a whole way of eating, and it has the longest track record of any.
Very low carbohydrate intake is not the answer either. When carbohydrate intake was tracked against mortality, the relationship was U-shaped: both very low and very high intakes carried higher risk, with the lowest risk around a moderate intake. At the low-carbohydrate end it mattered a great deal whether the fat and protein replacing carbohydrate came from animals or plants (Seidelmann et al., 2018). Neither extreme is the goal, and the source of the replacement food matters more than the amount cut.
Does Eating Fat Make You Fat?
Fat carries nine calories a gram against four for carbohydrate and protein, so gram for gram it is energy-dense. That did not translate into weight loss when the low-fat diet was tested directly. The Women's Health Initiative randomized nearly 49,000 postmenopausal women to a low-fat pattern for years, and their weight ended up only about 0.9 lb (0.4 kg) below the comparison group, too small a difference to matter (Howard et al., 2006).
Head-to-head trials point the same way. In DIETFITS, 609 adults ate either a healthy low-fat or a healthy low-carbohydrate diet for a year and lost almost the same amount, about 11.7 lb (5.3 kg) against 13.2 lb (6.0 kg), with neither genes nor insulin levels predicting who did better on which (Gardner et al., 2018). Both groups cut refined starch and sugar and leaned on whole foods, which the researchers named as the shared ingredient. Total calories and the quality of what you eat drive body weight, and the fat fraction does far less than the low-fat message claimed.
Butter, Tallow And Whole-Food Fats
That leaves butter, tallow, ghee and other animal fats close to ordinary. A systematic review of butter across more than 630,000 people found it essentially neutral for cardiovascular disease and stroke, with a small rise in overall mortality and a slightly lower risk of type 2 diabetes (Pimpin et al., 2016). Neutral is not beneficial. These are observational comparisons against whatever else people ate, often bread and refined starch, so a flat result reflects a low comparison bar as much as anything in the butter itself.
Whole-food fats eaten as part of an ordinary diet are fine, and what the fat comes with matters more than the fat itself. Butter on vegetables is different from butter in a pastry. Eggs are a fair example: for most people dietary cholesterol has only a small effect on blood cholesterol and is not clearly tied to heart disease, though a minority respond more strongly (Berger et al., 2015). The consistent benefit is from eating less processed food, whatever the fat content on the label.
Where Fat Clearly Harms
Industrial trans fat is the one fat that earned its bad name. Made by partially hydrogenating vegetable oil to keep it solid and shelf-stable, it is firmly linked to heart disease. The BMJ review found trans fat associated with higher coronary heart disease and death from it, and the long-standing estimate is that each 2% of calories from trans fat raises coronary risk about 23% (de Souza et al., 2015; Mozaffarian et al., 2006). It raises LDL, lowers HDL and promotes inflammation.
Industrial trans fat is the one dietary fat clearly shown to raise heart disease risk. Regulation, not food labels, is what removed it, so it can still appear wherever no legal cap is in force.
Countries have since removed industrial trans fat from the food supply, and the lead case is Scandinavian. Denmark became the first country in the world to cap it, limiting industrial trans fat to 2% of fats in 2003, the model the European Union and the WHO's global elimination push later followed. Danish researchers sampling supermarket foods across several European countries found industrial trans fat still present years later wherever no Danish-style limit was in force (Stender et al., 2016).
Naturally occurring trans fats, present in small amounts in dairy and meat, do not carry the same signal at ordinary intakes. The concern is the industrial kind, which reached people mostly through fried fast food, packaged baked goods and older margarines.
The findings behind this page, graded by strength and grouped by what they affect, are below.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Cholesterol And Lipids
Replacing saturated fat with polyunsaturated fat cut coronary events about 19%
In randomized trials, swapping saturated fat for polyunsaturated fat (from vegetable oils, nuts and seafood) lowered heart attacks and cardiovascular events by roughly a fifth.
Mozaffarian and colleagues pooled 8 randomized controlled trials (about 13,614 participants, 1,042 coronary events) in which polyunsaturated fat was increased in place of saturated fat, finding a 19% reduction in coronary heart disease events (RR 0.81, 95% CI 0.70 to 0.95), equivalent to about a 10% lower risk per 5% of energy substituted. Hooper and colleagues' 2020 Cochrane review of trials that reduced saturated fat found a 21% reduction in cardiovascular events (RR 0.79, 95% CI 0.66 to 0.93); its subgroup analysis did not find a significant difference between replacing saturated fat with polyunsaturated fat or with carbohydrate, attributing the benefit to the degree of saturated-fat and serum-cholesterol reduction.
The studies · 2
Mozaffarian et al., effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials · PLoS Med 2010;7(3):e1000252
Hooper et al., reduction in saturated fat intake for cardiovascular disease (Cochrane review) · Cochrane Database Syst Rev 2020;(5):CD011737
Dietary cholesterol raised LDL only about 7 mg/dL and was not clearly tied to heart disease
For most people, the cholesterol in food such as eggs has only a small effect on blood cholesterol and is not clearly tied to heart disease.
Berger and colleagues systematically reviewed 40 studies (17 cohort studies, reported across 19 publications) on dietary cholesterol. Dietary cholesterol was not statistically significantly associated with coronary heart disease or with ischemic or hemorrhagic stroke, and it produced a small but statistically significant average rise in serum total (about 11 mg/dL) and LDL (about 7 mg/dL) cholesterol, with the LDL rise attenuating at very high intakes. The authors rated the overall evidence as low quality, meaning the true effect could still differ from the summary. This is why blanket egg limits were relaxed in later dietary guidance.
The study · 1
Berger et al., dietary cholesterol and cardiovascular disease: a systematic review and meta-analysis · Am J Clin Nutr 2015;102(2):276-94
How it works
Saturated fat raised LDL more than any other fat, across 60 feeding trials
Saturated fat does raise LDL cholesterol, more than other fats do, though it also raises HDL, so the full blood-lipid picture is mixed.
Mensink and colleagues meta-analyzed 60 controlled feeding trials of the effect of dietary fats and carbohydrates on blood lipids. Isocaloric replacement of carbohydrate with saturated fat raised LDL cholesterol, and saturated fat raised LDL more than monounsaturated or polyunsaturated fat did. The same replacement raised HDL cholesterol and lowered fasting triglycerides, while leaving the total-to-HDL ratio essentially unchanged; only cis-unsaturated fats lower that ratio. LDL is a biomarker and an established risk factor, but it is a surrogate: the same food can nudge LDL up while its effect on heart attacks depends on what it replaces, which is why the biomarker and hard-outcome literatures can point different ways.
The study · 1
Mensink et al., effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids: a meta-analysis of 60 controlled trials · Am J Clin Nutr 2003;77(5):1146-55
Heart And Vascular
Each 2% of calories from industrial trans fat raised coronary risk about 23%
Industrial trans fat clearly raises the risk of heart disease, more strongly than any other fat.
De Souza and colleagues' 2015 systematic review of observational studies found trans fat intake associated with higher all-cause mortality (relative risk 1.34), coronary heart disease mortality (1.28) and coronary heart disease (1.21). Mozaffarian and colleagues' earlier synthesis estimated that each 2% of energy from trans fat raises coronary heart disease risk by about 23%, driven by trans fat raising LDL, lowering HDL, and promoting inflammation and endothelial dysfunction. This is the one dietary fat where the case for harm is strong and consistent, and it is why industrial trans fat has been removed from the food supply in many countries.
The studies · 2
de Souza et al., intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes · BMJ 2015;351:h3978
Mozaffarian et al., trans fatty acids and cardiovascular disease · N Engl J Med 2006;354(15):1601-13
Saturated fat by itself was not linked to more heart disease across 347,747 people
Pooling 21 long-term studies of almost 350,000 people, eating more saturated fat by itself was not linked to more heart disease or stroke.
Siri-Tarino and colleagues pooled 21 prospective cohort studies covering 347,747 subjects with 5 to 23 years of follow-up. The relative risk of coronary heart disease for the highest versus lowest saturated fat intake was 1.07 (95% CI 0.96 to 1.19), for stroke 0.81 (0.62 to 1.05), and for cardiovascular disease overall 1.00 (0.89 to 1.11), none statistically significant. The result says nothing about what people ate instead of saturated fat, which is the question the substitution analyzes answer.
The study · 1
Siri-Tarino et al., meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease · Am J Clin Nutr 2010;91(3):535-46
Replacing saturated fat with carbohydrate slightly raised coronary risk (hazard ratio 1.07)
Trading saturated fat for polyunsaturated fat lowered heart disease, but trading it for carbohydrate did not help and nudged risk slightly upward.
Jakobsen and colleagues pooled 11 prospective cohorts (344,696 people, 5,249 coronary events over 4 to 10 years). Replacing 5% of energy from saturated fat with polyunsaturated fat was associated with a hazard ratio of 0.87 for coronary events and 0.74 for coronary death. Replacing the same 5% with carbohydrate was associated with a hazard ratio of 1.07 (95% CI 1.01 to 1.14) for events, and monounsaturated-fat replacement showed no clear benefit. This is the substitution the low-fat era encouraged, and it was the wrong swap.
The study · 1
Jakobsen et al., major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies · Am J Clin Nutr 2009;89(5):1425-32
Butter looked roughly neutral for heart disease across 636,151 people
Butter came out roughly neutral for heart disease and stroke, with a tiny bump in overall mortality and a slightly lower diabetes risk.
Pimpin and colleagues systematically reviewed 9 cohort studies covering 636,151 participants and 6.5 million person-years. Per 14 g/day of butter, the relative risk was 1.01 for total mortality, 1.00 for cardiovascular disease, 1.00 for stroke and 0.96 for type 2 diabetes. The authors concluded butter is relatively neutral for cardiovascular and mortality outcomes and possibly slightly protective against diabetes, and cautioned that the comparison foods matter: butter against refined carbohydrate looks different from butter against olive oil.
The study · 1
Pimpin et al., is butter back? A systematic review and meta-analysis of butter consumption and risk of cardiovascular disease, diabetes, and total mortality · PLoS One 2016;11(6):e0158118
Longevity And Mortality
Highest total-fat intake tracked with 23% lower death risk across 18 countries (PURE)
In a large 18-country study, people eating the most total fat had a lower risk of dying over the follow-up, and people eating the most carbohydrate had a higher risk.
The PURE study (Dehghan et al.) followed 135,335 people aged 35 to 70 across 18 countries for a median 7.4 years. Comparing the highest with the lowest quintile, total fat carried a hazard ratio of 0.77 for total mortality, saturated fat 0.86, monounsaturated 0.81 and polyunsaturated 0.80; higher carbohydrate intake carried a hazard ratio of 1.28. Total fat and each fat type were not associated with myocardial infarction or cardiovascular death, and saturated fat was associated with lower stroke risk. The signal is strongest at the extremes of carbohydrate intake seen in low-income countries.
The study · 1
Dehghan et al., associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries (PURE) · Lancet 2017;390(10107):2050-2062
Death risk was lowest at 50 to 55% of calories from carbohydrate, higher at both extremes
Both very low-carb and very high-carb diets tracked with a shorter life; what mattered at the low-carb end was whether the fat and protein came from animals or plants.
Seidelmann and colleagues followed 15,428 adults in the ARIC cohort for a median 25 years and pooled the finding with studies totalling 432,179 people. The relationship between carbohydrate intake and mortality was U-shaped, with the lowest risk at 50 to 55% of energy from carbohydrate. Below 40% and above 70% both carried higher mortality. Among low-carbohydrate eaters, replacing carbohydrate with animal-derived fat and protein carried a hazard ratio of 1.18, while replacing it with plant-derived fat and protein carried 0.82. This is the nuance that keeps the page from tipping into fat-is-free.
The study · 1
Seidelmann et al., dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis · Lancet Public Health 2018;3(9):e419-e428
Weight And Fat Loss
A low-fat diet left nearly 49,000 women about 0.9 lb (0.4 kg) lighter after 7.5 years
Almost 49,000 women were asked to eat low-fat for years; their weight ended up essentially the same as the group who were not.
The Women's Health Initiative Dietary Modification Trial (Howard et al.) randomized 48,835 postmenopausal women to a low-fat eating pattern (target 20% of energy from fat, more fruit, vegetables and grains) or usual diet. The intervention group lost about 4.9 lb (2.2 kg) in the first year, but the difference from the comparison group narrowed to roughly 0.9 lb (0.4 kg) by year 7.5. There was a modest tendency for weight change to track the actual reduction in fat achieved, but cutting dietary fat did not produce meaningful lasting weight loss.
Who this may not transfer to:Measured entirely in postmenopausal women. Whether a low-fat pattern does more or less for weight in men or younger women was not tested here, though the head-to-head diet trials that did enrol both sexes point the same way.
The study · 1
Howard et al., low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial · JAMA 2006;295(1):39-49
Healthy low-fat and low-carb diets lost about the same, 11.7 lb (5.3 kg) versus 13.2 lb (6.0 kg) in a year
When people ate either a healthy low-fat or a healthy low-carb diet for a year, both groups lost about the same amount of weight.
The DIETFITS trial (Gardner et al.) randomized 609 overweight adults to a healthy low-fat or healthy low-carbohydrate diet, both emphasizing vegetables and minimally processed whole foods with no calorie target, for 12 months. Mean weight loss was 11.7 lb (5.3 kg) on low-fat and 13.2 lb (6.0 kg) on low-carbohydrate, a non-significant difference. Pre-specified analyzes found that neither a genotype pattern nor baseline insulin secretion identified who would succeed on which diet. Both groups were coached toward whole foods, which the authors highlighted as the shared ingredient.
The study · 1
Gardner et al., effect of low-fat vs low-carbohydrate diet on 12-month weight loss: the DIETFITS randomized clinical trial · JAMA 2018;319(7):667-679
Go Deeper
The threads on this page connect out to the rest of the library:
- Cholesterol and lipids, for the fuller picture of LDL, HDL and what actually moves cardiovascular risk, including the dietary-cholesterol and egg question in more depth.
- The Mediterranean diet, for the fat-swap on this page turned into a whole way of eating, with the trial and cohort record behind it.
- Seed oils, for the claim that vegetable and seed oils are toxic, weighed against what the replacement trials actually found.
- Whole foods, because the strongest signal in all of this is toward less processed eating, where fat content matters less than the food it comes in.
- How industry shapes science, for the wider story the sugar-and-fat episode belongs to, and how funding has bent research questions before.
- Type 2 diabetes, where the fat-versus-carbohydrate question and refined-carbohydrate intake sit at the center of the metabolic picture.
Common Questions
Is saturated fat bad for you?
On its own, the evidence is weaker than most people were taught. Pooled cohort studies of hundreds of thousands of people found saturated fat intake not significantly linked to heart disease or stroke. What the evidence does support is that saturated fat raises LDL cholesterol, and that replacing it with polyunsaturated fat lowers heart disease risk while replacing it with refined carbohydrate does not. So the question that matters is what you put in its place.
Does eating fat make you fat?
Not by itself. Fat is calorie-dense, but the low-fat diet failed the test when it was run: nearly 49,000 women assigned to eat low-fat for years weighed essentially the same as the comparison group, and head-to-head trials find low-fat and low-carbohydrate diets produce similar weight loss. Total calories and overall food quality drive body weight, not the fat fraction of the diet.
Is butter or tallow healthy?
Closer to neutral than to either extreme. A large review found butter roughly neutral for heart disease and mortality, with a slightly lower diabetes risk. That makes it ordinary food, not something to fear and not something to pile on, and what it is eaten with matters more than the butter itself. Whole-food fats as part of a real diet are fine; the case against processed and fractionated products is stronger than any case against butter itself.
Are seed oils toxic?
The trials point the other way. Vegetable and seed oils are the main source of the polyunsaturated fat that, when it replaced saturated fat in randomized trials, lowered coronary events about 19% and cardiovascular events 21%. There is no trial evidence of harm from these oils at ordinary dietary amounts. The reasonable caution is about what they are usually eaten in: much of it is fried fast food and packaged snacks, so the food matters more than the oil. The seed oils page weighs the toxicity claim in full.
What about trans fat?
This is the fat where the alarm is earned. Industrial trans fat, from partially hydrogenated oil, is firmly linked to higher heart disease risk, with each 2% of calories from it raising coronary risk about 23%. It raises LDL, lowers HDL and drives inflammation. Many countries have removed it from the food supply. Naturally occurring trans fats in dairy and meat, at the small amounts people actually eat, do not carry the same signal.
Do eggs raise my cholesterol?
For most people, only a little. A systematic review found dietary cholesterol not clearly associated with heart disease, and its effect on blood cholesterol small and inconsistent on average, a rise of about 7 mg/dL in LDL. A minority of people respond more strongly, sometimes called hyper-responders, so checking your own numbers tells you where you fall, but blanket egg limits were relaxed for good reason. The cholesterol-and-lipids page goes into this in more detail.
The Chinese Medicine View
Explore Related
Other pages this one connects to, by the evidence they share, the outcomes they touch, and the ground they cover.
All 13 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 10, 2026.
Evidence strength
How confidently the research supports a claim. Strength describes the evidence, not our endorsement.