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Despite half a century of research, there is still no high-quality evidence that natural saturated fat (from foods like butter and eggs) is anything but neutral from a health perspective.


In a recent analysis, 19 leading researchers concluded that it’s wrong to maintain the general advice to reduce saturated fat intake, as evidence does not support it.

A similar article was published in the Journal of the American College of Cardiology.


Another recent analysis of the field published in BMJ Evidence-Based Medicine concluded that: “The preponderance of evidence indicates that low-fat diets that reduce serum cholesterol do not reduce cardiovascular events or mortality. Specifically, diets that replace saturated fat with polyunsaturated fat do not convincingly reduce cardiovascular events or mortality. These conclusions stand in contrast to current opinion.”


Finally, a recent overview of the evidence linking saturated fat to heart disease, written by four prominent experts in the area, noted that when any fat, including saturated fat, replaces carbohydrate in the diet, there is improvement in important lipid markers related to risk of heart disease.


A 2009 systematic review of cohort studies and RCTs looking at potential relationships between dietary factors and heart disease concluded that “Insufficient evidence of association is present for intake of … saturated or polyunsaturated fatty acids; total fat … meat, eggs and milk”:

Archives of Internal Medicine 2009: A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease [moderate evidence]
Similarly, a 2010 review of cohort studies found “…no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD”:

The American Journal of Clinical Nutrition 2010: Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease [moderate evidence]
Meta-analyses of observational studies in 2015 and 2017 reached the same conclusions about the lack of association between saturated fat and heart disease:

British Medical Journal 2015: Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies [moderate evidence]

British Journal of Sports Medicine 2017: Evidence from prospective cohort studies does not support current dietary fat guidelines: a systematic review and meta-analysis [moderate evidence]
The most recent systemic review of RCTs published in 2020 found eating less saturated fat was associated with a small reduction in cardiovascular events, but with no difference in risk of death. However, when analyzed based on cholesterol and study quality, any deleterious effect vanished.


Cochrane Database of Systemic Reviews 2020: Reduction in saturated fat intake for cardiovascular disease [systematic review of randomized trials; strong evidence]

Two other systematic reviews of RCTs, also showed no convincing evidence that saturated fat is harmful.

In these reviews, researchers concluded that replacing saturated fats with unsaturated fats might slightly reduce the risk of heart attack and other cardiovascular events by about 14 to 19 percent.

However, in the first of these review, the reduction in risk was seen only in studies of at least two years duration and in studies of men, but not of women; furthermore, these changes appeared to have no effect on total or heart disease mortality:

Cochrane Database of Systematic Reviews 2011: Reduced or modified dietary fat for preventing cardiovascular disease [strong evidence]

In the second systematic review, for five of the eight studies analyzed there was insufficient evidence to conclude that the group outcomes were statistically significantly different from each other:

PloS Med 2010: Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials [strong evidence]
In addition, other more recent systematic reviews of RCTs haven’t shown any reduction in heart diease risk as a result of substituting saturated fats with unsaturated fats:

Nutrition Journal 2017: The effect of replacing saturated fat with mostly n-6 polyunsaturated fat on coronary heart disease: a meta-anlysis of randomised controlled trials [strong evidence]

Open Heart 2016: Evidence from randomised controlled trials does not support current dietary fat guidelines: a systematic review and meta-analysis [strong evidence]

Annals of Internal Medicine 2014: Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis [strong evidence]

British Medical Journal 2013: Dietary fatty acids in the secondary prevention of coronary heart disease: a systematic review, meta-analysis and meta-regression [strong evidence]
When it comes to butter and other high-fat dairy specifically, there is some observational evidence that people consuming it might be, if anything, thinner and healthier than others.

In 2012, researchers exploring the relationship between full-fat dairy, heart health, and weight concluded that “the observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk”:

European Journal of Nutrition 2012: The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease [weak evidence]

In fact, follow-up on the PURE study with over 177,000 subjects revealed no association between saturated fat intake and heart disease but did show saturated fat was linked to decreased risk for all-cause mortality and stroke. While this is weak observational data, it does make it much less likely that saturated fat in dairy is intrinsically harmful harmful

The Lancet 2017: Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study [very weak evidence]

The evidence above indicates that dietary advice to avoid fat in general and saturated fat in particular is based on a very weak scientific foundation.
Learn more: A user guide to saturated fat

Polyunsaturated fats and the Sydney Diet Heart Study
Advice to replace saturated fats with polyunsaturated fats – to reduce heart disease risk – is controversial, and the evidence supporting this guidance comes mostly from older studies with many weaknesses.

A re-evaluation of one of these, the Sydney Diet Heart Study, uncovered previously unpublished data showing a trend toward increased risk of death and heart disease in the group who got polyunsaturated omega-6 fats as a replacement for saturated fat in their diets.

When this data is included in a meta-analysis of other studies where saturated fats are replaced with polyunsaturated omega-6 fats, the almost-significant trend towards increased heart disease and death from heart disease shows that this replacement does not appear to have health benefits.

British Medical Journal 2013: Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis [strong evidence]

Similar results were seen in the Minnesota Coronary Experiment, showing no health benefits to replacing saturated fats with polyunsaturated fats.

BMJ 2016: Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73) [strong evidence]

However, there is much conflicting data ranging from mechanistic studies to RCTs. Read more in our evidence-based guide to vegetable oils.
The PURE study
A recent large observational study published in The Lancet shows that when diverse global populations are surveyed, diets with lower fat and higher carbohydrate content do not confer any health advantage.

The PURE study followed over 135,000 people in 18 countries from five continents for over seven years.
The researchers found that people who ate the most carbohydrate died earlier. A higher intake of fat, on the other hand, was linked to longer life, regardless of whether the fat was unsaturated or saturated.

This is an observational study and therefore cannot prove that eating fewer carbs and more fat extends life. However, it does call our current dietary advice into question, as the authors note: “Global dietary guidelines should be reconsidered in light of these findings.” Learn more

The Lancet 2017: Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study [weak evidence]

DD Podcast interview with Prof. Andrew Mente, one of the co-authors of the PURE study

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