A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion
Liu et al. Nutrition Journal
A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion
Ann G. Liu 4
Nikki A. Ford 3
Frank B. Hu 2
Kathleen M. Zelman 6
Dariush Mozaffarian 5
Penny M. Kris-Etherton 0 1
0 319 Chandlee Laboratory, Pennsylvania State University , University Park, Pennsylvania, PA 16802 , USA
1 Department of Nutritional Sciences, Pennsylvania State University , University Park, Pennsylvania, PA , USA
2 Departments of Nutrition and Epidemiology, Harvard T.H. Chan School of Public Health , Boston, MA , USA
3 Director of Nutrition, Avocado Nutrition Center , Mission Viejo, CA , USA
4 Freelance Medical Writer , West Lafayette, IN , USA
5 Tufts Friedman School of Nutrition Science & Policy , Boston, MA , USA
6 Director of Nutrition, WebMD , Marietta, GA , USA
Consumers are often confused about nutrition research findings and recommendations. As content experts, it is essential that nutrition scientists communicate effectively. A case-study of the history of dietary fat science and recommendations is presented, summarizing presentations from an Experimental Biology Symposium that addressed techniques for effective scientific communication and used the scientific discourse of public understanding of dietary fats and health as an example of challenges in scientific communication. Decades of dietary recommendations have focused on balancing calorie intake and energy expenditure and decreasing fat. Reducing saturated fat has been a cornerstone of dietary recommendations for cardiovascular disease (CVD) risk reduction. However, evidence from observational studies and randomized clinical trials demonstrates that replacing saturated fat with carbohydrates, specifically refined, has no benefit on CVD risk, while substituting polyunsaturated fats for either saturated fat or carbohydrate reduces risk. A significant body of research supports the unique health benefits of dietary patterns and foods that contain plant and marine sources of unsaturated fats. Yet, after decades of focus on low-fat diets, many consumers, food manufacturers, and restauranteurs remain confused about the role of dietary fats on disease risk and sources of healthy fats. Shifting dietary recommendations to focus on food-based dietary patterns would facilitate translation to the public and potentially remedy widespread misperceptions about what constitutes a healthful dietary pattern.
The way consumers obtain nutrition information has
changed substantially in the past two decades. Use of the
internet and social media has grown rapidly, and these
are now among the leading sources of information for
health and wellness. Perhaps due to access to more
information than ever, including conflicting information of
uncertain and variable quality, many consumers are
more confused than ever.
Nutrition scientists are trusted content experts [
Consequently, it is essential that they effectively communicate
research findings to policy makers, authoritative bodies
and the general public in order for consumers to make
sound, evidence-based dietary decisions. In addition,
communicating scientific findings can be viewed as a civic
] and has been suggested to be included in formal
academic training [
]. Yet, scientists’ ability to
communicate is less than other professionals [
Within the nutrition community, one example of
suboptimal communication between scientists and the public
is the continued demonization and general avoidance of
dietary fat [
]. For years, an emphasis of nutrition
communication was to balance calorie intake and energy
expenditure and decrease dietary fat. Reductions in total dietary
fat were recommended to reduce saturated fat as well as
due to the energy density of lipids and the overall goal to
reduce caloric intake [
]. Partly as a result, low-fat,
highcarbohydrate diets were recommended in 1980 and
thereafter for weight loss and reducing cardiovascular disease
(CVD) risk. However this led to unintended
consequences. The focus on reducing total fat resulted in
increased consumption of refined carbohydrates and
added sugars, and avoidance of nutrient-dense foods rich
in healthy unsaturated fats such as nuts, seeds, avocados
and vegetable oils. Subsequently, fat consumption has
decreased while carbohydrate intake has increased as
percentage of calories, which has been accompanied by
significant increases in total energy intake and obesity
rates in the United States [
While single nutrient targets have worked well for
treating diseases of deficiency, this has been problematic
for addressing chronic diseases [
]. In contrast, specific
foods and overall dietary patterns can substantially affect
chronic disease risk [
]. However, by attributing their
effects to single nutrients, foods with very different
physiological effects can become conflated and
contribute to consumer confusion. A global survey found that
95% of respondents knew that vitamins were needed for
a healthy diet, but only 41% knew certain fats were
essential nutrients [
]. In recent decades, we have gained
substantial knowledge regarding the role of broad classes
of nutrients and foods in major chronic diseases. In
addition, challenges in communicating science clearly to
the public contributes to consumer confusion and, as a
result, may have public health consequences. This paper
summarizes an Experimental Biology Scientific Session
for which the goals were to discuss the history of
recommendations for dietary fat and evidence showing health
benefits of unsaturated fats from plant sources in order
to provide context for the strategies described to
improve nutrition science communications to the public.
Case study: Dietary fat
History of dietary fat recommendations
Reducing dietary saturated fat has been a cornerstone
of recommendations for reducing CVD risk for
decades, largely based on the classic diet-heart
hypothesis which proposes that dietary saturated fat and
cholesterol play a primary role in the development of
atherosclerosis and coronary heart disease (CHD).
This hypothesis was informed by two key
observations: 1) controlled feeding trials demonstrated that
dietary saturated fatty acids and cholesterol raised
serum total cholesterol and low density lipoprotein
cholesterol (LDL-C) levels, and 2) increased serum
total cholesterol and LDL-C predicted risk of CHD
]. Since the origin of the diet-heart hypothesis, a
large body of research has identified multiple
pathways that mediate the development of CHD. Thus,
interventions that affect single surrogate biomarkers
must be interpreted with caution [
apolipoprotein B-carrying LDL-C particles are established
causal determinants of CVD risk, there are many
other CVD risk factors that substantially affect disease
development including other blood lipids and
lipoproteins, hypertension, smoking, diabetes,
overweight and obesity. Dietary fats have complex and
sometimes divergent effects on these different
contributors to CVD risk. Though views of the original
diet-heart hypothesis continue to evolve, they have
had long-lasting effects on nutrition policy and
consumer perceptions of fat. Decades of
recommendations to consume low-fat diets and the proliferation
of low-fat products have greatly influenced consumer
perceptions of fat.
Current recommendations for dietary fat intake
The percentage of energy consumed as fat can vary
widely, and the diet can still meet energy and
nutrient needs. Current recommendations from various
organizations regarding fat intake in adults are
summarized in Table 1 [
]. Dietary guidelines
from the World Health Organization and the Dietary
Reference Intakes recommend a total fat intake
between 20 and 35% of total calories [
minimum of 20% is to ensure adequate consumption
of total energy, essential fatty acids, and fat-soluble
] and prevent atherogenic dyslipidemia
(low high-density lipoprotein cholesterol (HDL-C),
high triglyceride-rich lipoproteins) which occurs with
low-fat, high carbohydrate diets and increases risk of
coronary heart disease [
]. The maximum of 35%
was based on limiting saturated fat and also the
observation that individuals on higher fat diets consume
more calories, resulting in weight gain [
Tolerable Upper Intake Level was set for total fat because
there is no intake level for which there is an adverse
]. Of note, the 2015 Dietary Guidelines
Advisory Committee placed emphasis on the types and
quality of foods consumed and did not set an upper
limit for total fat based on the lack of supporting
]. This was reflected in the Dietary
Guidelines for Americans 2015–2020, which emphasizes
types of fat within the context of a healthy dietary
The 2015 Dietary Guidelines Advisory Committee, the
Dietary Guidelines for Americans 2015–2020, and many
other organizations consistently recommend a limitation
on intake of saturated fat, typically to <10% of energy
]. In contrast, Canada’s Heart and Stroke
Foundation recently removed any specific limitation on
saturated fat, stating instead that their dietary guidelines do
“not include a threshold or limit for saturated fat and
instead focus on a healthy balanced dietary pattern” .
The role of saturated fat for CHD, and the
corresponding controversy, is discussed further below.
The Institute of Medicine determined that there is
no safe level of consumption of industrial trans fats
from partially hydrogenated oils. Trans fats
adversely affect a diverse range of CVD risk factors:
they raise LDL-C, raise triglycerides, lower HDL-C,
increase inflammation, promote endothelial
dysfunction, and may promote hepatic fat synthesis,
resulting in far greater risk of developing CHD than any
other macronutrient. Based on these effects, the
recommendation is to limit their intake as much as
]. Denmark was one of the first
countries to ban the sale of products containing trans
fats in 2003 and since that time the European
Union has taken a stance to reduce trans-fats in the
food supply [
] and, at the same time, the US
Food and Drug Administration ruled in 2015 that
partially hydrogenated oils are no longer Generally
Recognized as Safe and should be removed from the
food supply [
Like saturated fats, cis-monounsaturated fatty acids (MUFA)
are readily synthesized by the liver in response to
carbohydrate consumption [
]. They are not required in the diet;
thus no Adequate Intake or Recommended Dietary
Allowance has been set [
]. In addition, there is
little evidence to set a Tolerable Upper Intake Level
]. The major MUFA in Western diets is oleic acid
which is abundant in both animal and plant sources
]. Most dietary guidelines for MUFA consumption
are based on subtraction of recommended intakes of
saturated fat and polyunsaturated fat from total fat
rather than evidence for specific optimal intakes of
MUFA per se.
Cis-polyunsaturated fatty acids (PUFA) include essential
fatty acids and have beneficial roles in human health.
However, formal clinical deficiency of n-6 and n-3 fatty
acids is rare in healthy individuals in the United States
and most other countries. More than a decade ago, the
IOM set definitions of Adequate Intakes for linoleic and
α-linolenic acid based on median US population intakes,
with up to 10 % of the recommended total n-3 PUFA
intake being eicosapentaenoic acid (EPA) and/or
docosahexaenoic acid (DHA) [
]. These US Dietary Reference
Intakes, based on evidence published prior to 2000, have
not been updated. More recently, the United Nations
Food and Agriculture Organization set new target
Acceptable Macronutrient Distribution Ranges for adults for
linoleic acid (2.5–9% of energy), total n-3 PUFA (0.5–2%
of energy), and EPA + DHA (250 to 2000 mg/d) [
Trends in consumption of dietary fats
Since 1971, the average fat intake in the United States
has decreased from 36.6 to 33.6% [
]. The median intake
of saturated fat currently is 9.7–11.1% depending on sex
and race or ethnic subgroup, and approximately 42–65%
of the adult population consumes greater than the
recommended level of 10% of calories from saturated fat
]. Since 1980, when the first Dietary Guidelines for
Americans were issued, the intake of saturated fat has
steadily decreased as a percent of calories. The decrease
in total and saturated fat intake (as a %) since the 1980’s
has largely reflected a corresponding increase in energy
from dietary carbohydrate.
These dietary trends are not unique to the U.S. Data
from the Australian Health Survey 2011–2013 show
dietary trends mirroring those observed in the U.S. [
Additionally, a report by the USDA Economic Research
Service compared food availability and dietary
preferences and behavior between the U.S. and the European
Union and concluded that the diets are more similar,
than not and both the U.S and EU have reduced fat
consumption over time [
Role of saturated, monounsaturated, and polyunsaturated
fat in coronary heart disease
Saturated and monounsaturated fatty acids are
synthesized in the body for energetic, physiological, and
structural functions, and they are present in many foods. For
example, palmitic acid, the major saturated fatty acid in
the diet, is synthesized in the liver from starch and sugar
via de novo lipogenesis, and it is the predominant fatty
acid present in dairy and meats [
]. Due to the positive
linear relationship between total saturated fat intake and
LDL-C concentrations, the recommendation is to limit
saturated fat to <10% of calories [
]. However, the
role of saturated fat in heart disease is complex because
of the heterogeneous biological effects of the different
saturated fatty acids and the diversity of food sources
. Moreover, conclusions are complicated by dietary
substitutions underscoring the importance of
considering the replacement nutrient.
Ecological and migration studies including the seminal
Seven Countries Study by Ancel Keys have found strong
positive correlations between saturated fat intake and
CHD rates [
]. However, these studies are confounded
by other environmental factors associated with different
countries such as culture, geography, and economic
development. Prospective cohort studies provide better
evidence for dietary habits and CHD because
adjustments are made for individual-level differences in major
risk factors, lifestyle habits, and other confounding
factors. While, these types of studies have consistently
found that higher trans fat intake is associated with
elevated risk of coronary heart disease [
], the effects of
dietary saturated fat on coronary heart disease risk are
less consistent [
]. A 2010 meta-analysis of prospective
cohort studies by Siri-Tarino et al. found no relationship
between total saturated fat and risk of coronary heart
]. Similarly, a 2014 meta-analysis by
Chowdhury et al. found no significant relationship between total
saturated fat or total polyunsaturated fat consumption
and risk of CHD [
]. These studies assessed the
association of variations in saturated fat intake in the
population, rather than modeling the specific substitution of
saturated fat with other macronutrients. Studies
specifically modeling the comparison of saturated fat to total
carbohydrate have shown saturated fat to have similar
associations with cardiovascular risk compared to total
]. Based on all the evidence, the
2015 Dietary Guidelines Advisory Committee concluded
that replacing saturated fat with total carbohydrates does
not reduce risk of CVD . Recently, an AHA
Presidential Advisory reviewed the scientific evidence and
concluded that lowering intake of saturated fat and
replacing it with unsaturated fats, especially
polyunsaturated fats will lower the incidence of cardiovascular
An alternative method for evaluating health effects of
macronutrients is to consider the specific replacement
nutrient. Such models do not compare differences in
diet as actually consumed in the population, but provide
estimates about potential health effects of specific
interreplacements of different macronutrients. In such
models, the observed effects can be due to reduced
intake of one nutrient, increased intake of the other, or
both. Such models also raise complexities in
understanding the biological effects of individual fatty acids within
the context of food matrices and dietary patterns, which
each provide a milieu of nutrients, bioactive compounds,
and other constituents that may modulate the effects of
the fatty acids.
In cohort studies modeling specific replacement
nutrients, there is consistent evidence that polyunsaturated
fatty acids are the most beneficial replacement nutrient
for CVD risk reduction as compared to either saturated
fat or total carbohydrate. Jakobsen et al. pooled 11
cohort studies with over 344,000 participants and found
that isocalorically replacing saturated fat with PUFA was
associated with reduced risk of coronary events (per 5%
energy, hazard ratio: 0.87; 95% CI: 0.77, 0.97) and
coronary death (hazard ratio: 0.74; 95% CI: 0.61, 0.89) [
a recent analysis, Li, et al. found that replacing saturated
fat with high quality carbohydrates such as whole grains
was associated with lower risk of CHD, but replacing
saturated fat by total carbohydrates or refined starch/
added sugars was not associated with CHD risk [
contrast, other analyses, including a large pooling project
that included the prior cohorts, suggest that total
saturated fat is superior to total carbohydrate for CHD risk,
and that refined starch/added sugars are more harmful
than saturated fat. In the pooling project, isocalorically
replacing saturated fat intake with either total carbohydrate
or total MUFA did not result in reduced risk of coronary
events; in fact, consuming total carbohydrate in place of
saturated fat was associated with significantly higher risk
(hazard ratio: 1.07; 95% CI: 1.01, 1.14) [
]. A recent
publication of women from the Nurses’ Health Study and
men from the Health Professionals Follow-up Study found
that replacing carbohydrates with saturated fat was not
associated with CHD mortality, while replacing
carbohydrates with unsaturated fats significantly reduced CHD
]. Furthermore, substituting unsaturated fats for
saturated fats (5% energy) reduced total mortality and
mortality from CHD, cancer and neurodegenerative
diseases (Fig. 1). A new study [
] reported that substituting
plant protein for long chain SFA decreased risk of CHD.
Another observational study found that replacing
saturated fat with low glycemic index carbohydrates was
associated with a nonsignificant trend toward lower risk of
myocardial infarction, while replacement of saturated fat
with high glycemic index carbohydrates was associated
with significantly higher risk (hazard ratio: 1.33; 95% CI:
1.08, 1.64) [
]. The effects of replacing saturated fat with
different types of carbohydrates require further
The similar associations of total carbohydrate vs.
saturated fat with CHD (or in the largest studies, actually
beneficial associations of saturated fat compared with
total carbohydrate) might suggest that guidelines could
include a limit on the sum of total carbohydrate plus
saturated fat. The new research suggests that rather than
focusing on total carbohydrate, the guidance should be
on specific foods: limiting foods rich in refined starch
and sugars, while eating more of other
carbohydratecontaining foods such as fruits, legumes, and fiber-rich
whole grains. Likewise, the new research suggests that
rather than focusing on total saturated fat, the guidance
also could be on specific foods, as saturated fat from
different major food sources is associated with higher risk,
no risk, or even lower risk of CHD, depending on the
food source [
]. For example, studies utilizing
objective circulating biomarkers of fat intake identify
protective associations of odd-chain saturated fats, largely
consumed from dairy saturated fat, and risk of CHD
. These findings suggest that the specific matrix of
different foods – including other fatty acids, nutrients,
and bioactives – may biologically modify the effect of
saturated fat on CHD. As is evident, this approach could
be adopted for any single nutrient in the diet for
providing food-based dietary guidance that also considers
specific nutrient recommendations. Provocative new
evidence suggests that we are at the beginning of a new
era for making food-based dietary recommendations that
requires more research and debate to reach scientific
When all these lines of evidence are considered, the
role of saturated fat in CHD is controversial, including
among the writing group of the present manuscript.
Some scientists believe that reduction in saturated fat
must continue to be prioritized, based on its
LDLraising effects and causality for CVD, on the benefits of
replacing saturated fat with PUFA, and on concerns that
in the absence of recommendations to limit saturated
fat, ingredients high in saturated fat (e.g., palm oil) could
be added to foods. Other scientists believe that
heterogeneous effects of saturated fat on blood lipids and
lipoproteins, of different individual saturated fatty acids, and
of saturated fat from different food sources raises
questions on the biologic and practical relevance of any focus
on saturated fat, and that food-based recommendations
are both more biologically sound and more practical.
Epidemiological evidence on the association of total
dietary MUFA from all sources with CHD has been
13, 34, 40
]. A recent study, however, with Nurses’
Health Study and Health Professional Follow-up Study
data estimated that replacing 5% of energy from
saturated fat with MUFA was associated with a 15% lower
risk of CHD [
]. In addition, another recent study has
shown that replacement of saturated fat with MUFA
(principally from plant sources) decreases CHD risk
]. This observation likely reflects an increase in
consumption of plant-based MUFA sources such as olive oil
and a decreased consumption of animal-based MUFA
sources from red meat over time, and thus the
association for MUFA was less confounded by saturated
fat. However, this finding needs to be confirmed in
Many lines of evidence support CHD benefits PUFA
consumption, whether as a replacement for saturated
fat or carbohydrate. A meta-analysis of prospective
cohort studies found that increased consumption of
linoleic acid was associated with a 15% lower risk of
CHD events (relative risk: 0.85; 95% CI: 0.78–0.92)
and a 21% lower risk of CHD death (relative risk:
0.79; 95% CI: 0.71–0.89) [
]. The relationship was
dose-responsive (Fig. 2) and independent of other
traditional CHD risk factors and dietary factors such
as fiber and α-linolenic acid [
]. Notably, benefits
were similar irrespective of whether linoleic acid
replaced saturated fat or total carbohydrate (which is
often mostly refined).
Evidence from clinical trials also supports the health
benefits of increasing PUFA for reducing CHD risk.
Mozaffarian et al. evaluated the effect of increased PUFA
consumption, as a replacement for saturated fat, on
CHD in a meta-analysis of randomized controlled trials
]. Eight trials met inclusion criteria and encompassed
13,614 participants and 1042 coronary events
(myocardial infarction or cardiac death) [
]. Average weighted
PUFA consumption was 14.9% of energy in intervention
groups and 5.0% in control groups. Increased PUFA
consumption resulted in a 19% decrease in CHD risk
(relative risk: 0.81; 95% CI: 0.70–0.95) [
]. Each 5% increase
in energy from PUFA corresponded to a 10% decrease in
CHD risk. Pooling across different types of evidence,
consistent beneficial effects are seen when PUFA is
increased, but not when SFA is replaced with carbohydrate
or MUFA (Fig. 3) [
30, 34, 42
]. These studies provide
compelling evidence that consumption of PUFA reduces
A growing body of literature suggests that both n-6
and n-3 fatty acids confer benefits for a wide range of
conditions, in particular CVD, and also possibly
diabetes, cancer, and autoimmune diseases [
30, 41, 43–46
The results of recent randomized controlled trials of n-3
PUFA supplements on cardiovascular outcomes have
been disappointing; theorized reasons include the
possibility that n-3 PUFA have little additional effect on top
of modern drug therapies for CVD, as well as the study
designs employed [
]. However, these relatively
short-term trials in high-risk populations may not be
generalizable to the observed beneficial associations in
generally healthy populations consuming dietary sources
of n-3 PUFA such as fish [
]. Further research is
needed to better determine how different approaches to
food processing, technology, stability/oxidation, and
breeding/engineering of plants or animals may alter the
overall health effects of PUFA and MUFAs.
Clinical interventions – Dietary patterns
Recent clinical evidence also supports the hypothesis
that including plant and seafood sources of PUFA and
MUFA in the diet improves cardiometabolic risk factors.
Mediterranean diets generally derive a relatively high
proportion of calories from fat (typically 35–40% of kcal or
more) with much of the fat calories coming from plant and
vegetable oils sources of MUFA [
diets commonly emphasize consumption of fruits,
vegetables, legumes, fish, nuts, and olive oil [
]. In the
Prevención con Dieta Mediterránea (PREDIMED) trial, 7447
persons were counseled to consume a Mediterranean diet
supplemented with extra-virgin olive oil (50 g/day), a
Mediterranean diet supplemented with mixed nuts (30 g/day;
15 g of walnuts and 7.5 g of almonds and 7.5 g of
hazelnuts), or a control diet reduced in dietary fat [
]. After a
mean follow-up of 4.8 years, consumption of a
Mediterranean diet supplemented with either extra-virgin olive oil or
nuts resulted in a 30% reduction in risk of myocardial
infarction, stroke, or death (hazard ratio: 0.70; 95% CI: 0.54,
0.92 and hazard ratio: 0.72; 95% CI: 0.54, 0.96) [
Several secondary analyses of the PREDIMED trial
have demonstrated other potential health benefits of
consuming a Mediterranean diet. A Mediterranean diet
supplemented with extra-virgin olive oil or nuts resulted
in significant reductions in diastolic blood pressure, 24-h
ambulatory blood pressure, fasting blood glucose, and
total cholesterol [
]. There were also reductions in
biomarkers of vascular wall inflammation, which may
partially explain the cardioprotective effects seen in the
main study . Participants who consumed a
Mediterranean diet supplemented with extra-virgin olive oil or
nuts also had a 52% reduction in diabetes incidence
compared to the control group (hazard ratio: 0.47; 95%
CI: 0.25, 0.97 and hazard ratio: 0.48; 95% CI: 0.24, 0.96)
]. This suggests that changes in dietary patterns can
have multifactorial health benefits beyond CVD.
The Dietary Approaches to Stop Hypertension (DASH)
dietary pattern is also beneficial for reducing CVD risk. The
original DASH diet emphasized vegetables, fruits, whole
grains, low-fat dairy products, poultry, fish, and nuts while
limiting sweets and red meats, and was generally higher in
carbohydrates and lower in total fats. At the end of the
eight-week dietary intervention, systolic and diastolic blood
pressure were significantly reduced by 5.5 and 3.0 mmHg
compared to the control diet [
]. Consumption of the
DASH diet also resulted in lower total cholesterol, LDL-C,
and HDL-C levels with no changes in triglycerides or total
cholesterol:HDL-C ratio [
]. As a follow up to the DASH
trial, the Optimal Macronutrient Intake Trial to Prevent
Heart Disease (OmniHeart) was conducted to compare
high-carbohydrate, high-protein, or high-MUFA versions of
the original DASH diet. Participants with prehypertension
or stage 1 hypertension were fed for 6-week periods in a
3period randomized crossover trial. While all diets improved
blood pressure and LDL compared to baseline, the diets
that replaced saturated fat with protein or especially
vegetable unsaturated fats (principally olive oil) resulted in
greater improvements in CVD risk factors compared to the
carbohydrate-rich diet [
These studies demonstrate consistent themes of dietary
patterns that effectively reduce CVD risk. Accordingly, the
2015 Scientific Report of the Dietary Guidelines Advisory
Committee concluded, “A healthy diet can be achieved in
multiple ways and preferably with a wide variety of foods
and beverages.” [
]. They also identified common
features of beneficial dietary patterns across diverse health
outcomes including cardiovascular disease, obesity, and
cancer. The committee recommended healthy dietary
pattern options that: 1) emphasize vegetables, fruits, whole
grains, seafood, legumes, and nuts, 2) include moderate
amounts of low-fat dairy products and alcohol (among
adults, if consumed), 3) are lower in red and processed
meats, 4) limit refined grains and sugar-sweetened foods
and beverages [
Clinical interventions – Specific foods and oils
Several studies have examined the potential benefits of
incorporating specific foods and oils on cardiometabolic
risk factors. As described above, PREDIMED
demonstrated reductions in CVD events with either mixed nuts
or extra-virgin olive oil. A systematic review and
metaanalysis examined the relationship between nut
consumption and blood lipid levels. A total of 61 trials (42
randomized, 18 non-randomized) totaling 2582 unique
participants provided nuts to participants for durations
ranging from 3 to 26 weeks [
]. Compared with
controls, each daily serving of nuts lowered LDL-cholesterol
(−4.8 mg/dL; 95% CI: -5.5, −4.2) [
]. These results
complement previous findings from a pooled analysis of
intervention trials examining the relationship between
nut consumption and blood lipid levels [
trials comprising 583 participants were included.
Interventions were at least 3 weeks in duration and nut
consumption was the only dietary intervention [
consumption (average 67 g/day) significantly reduced
total cholesterol, LDL-C, and total cholesterol to HDL-C
]. Both studies are in agreement with the large
body of epidemiological evidence showing an association
between increased nut consumption and decreased risk
of CHD [
Olive oil is the main fat source in the Mediterranean
diet, and it is believed to confer some of the
cardioprotective benefits of the diet. Olive oil is high in MUFAs
and contains phenolic compounds, which have
antioxidant and anti-inflammatory properties [
clinical trials in healthy men have observed small
increases in HDL-C, decreases in triglycerides, and
reductions in systolic blood pressure with olive oil
]. Oxidative stress markers
decreased with increasing polyphenol content of the olive
oil . These studies complement a previous
observational study, which found an inverse association between
olive oil consumption and both systolic and diastolic
blood pressure [
]. In addition, the results are
consistent with a study conducted with Nurses’ Health Study
and Nurses’ Health Study II data that showed that
substituting olive oil for stick margarine, butter, or
mayonnaise was associated with a modestly lower risk of type 2
diabetes in women [
The Canola Oil Multi-center Intervention Trial
(COMIT) sought to determine the effects of different oil
blends with varying levels of n-9 MUFA, n-6 PUFA, and
n-3 PUFA on biomarkers of coronary heart disease risk
]. Participants were fed a controlled weight
maintenance diet supplemented with one of 5 liquid vegetable
oil treatments in a randomized crossover design.
Treatments included: 1) conventional canola oil (Canola; n-9
rich), 2) high-oleic acid canola oil with docosahexaenoic
acid (CanolaDHA; n-9 and n-3 rich), 3) a blend of corn
and safflower oil (25:75) (CornSaff; n-6 rich), 4) a blend
of flax and safflower oils (60:40) (FlaxSaff; n-6 and
shortchain n-3 rich), or 5) high-oleic acid canola oil
(CanolaOleic; highest in n-9). All treatments lowered total
cholesterol and LDL-C [
]. The CanolaDHA blend
significantly increased HDL-C, lowered triglycerides. The
CanolaDHA blend had the greatest systolic and diastolic
pressure-lowering effect. All treatments lowered the
Framingham 10-year coronary heart disease risk score; the
CanolaDHA treatment decreased it the most [
Foods high in plant sources of MUFA also have
beneficial effects. A randomized crossover trial of the health
benefits of daily avocado consumption was conducted
with overweight or obese participants fed three
cholesterol-lowering diets: 1) lower fat diet (24% fat), 2)
moderate-fat diet (34% fat), and 3) moderate-fat diet
supplemented with one avocado per day [
]; the latter
two diets were matched for macronutrients. All three
diets decreased LDL-C and total cholesterol compared to
]. The moderate-fat diet supplemented with
avocado resulted in significantly greater reductions in
LDL-C and total cholesterol than either the lower-fat or
moderate-fat diet [
]. Additionally, the
avocadocontaining diet significantly reduced LDL particle
number, small dense LDL, and the ratio of LDL-C/HDL-C
]. These studies provide evidence of the
lipidlowering potential of plant foods that are rich in PUFA
and MUFA. The results of this study also suggest
additional benefits of nutrients/bioactives in avocados
beyond their healthy fat composition.
Interestingly, there have also been some studies
suggesting possible cardioprotective benefits of certain
foods high in saturated fats such as dark chocolate and
specific dairy products. Meta-analyses of randomized
controlled trials investigating the effects of chocolate or
cocoa products have found inverse associations between
cocoa consumption and total cholesterol, LDL-C, blood
pressure, and serum insulin [
]. These effects have
been attributed to the flavanols found in dark chocolate
and cocoa products. Dairy products encompass a widely
varied group of foods including butter, milk, cheese, and
yogurt. Epidemiological studies have generally found no
association or modest inverse associations between dairy
product intake and risk of CVD [
]. Clinical studies
have been mixed depending on the dairy product and
the comparator investigated. Butter and whole milk
increase total cholesterol and LDL-C . Cheese
consumption seems to modestly lower LDL-C when
compared to butter [
]. Yogurt consumption may
produce favorable changes in LDL-C, HDL-C, and
triglycerides, but the effects seem to be highly dependent on the
strain of bacteria used for fermentation [
cohort studies indicate a consistent inverse association
between yogurt consumption and risk of type 2 diabetes,
although the association between other dairy products
and diabetes risk has been inconsistent [
]. A recent
] of meta-analyses designed to evaluate
associations between individual foods (and relevant to
this paper, foods with different fat types) and coronary
heart disease, stroke and diabetes is shown in Fig. 4. As
is evident, nuts and seeds consistently show benefits, fish
benefits CHD death and stroke but not diabetes, and
dairy products, including total dairy, milk, cheese, butter,
and yogurt demonstrate inconsistent associations. For
processed red meats, there is clear evidence of increased
associations with cardiometabolic diseases, whereas for
unprocessed red meats, there is evidence for increased
stroke and diabetes risk [
]. As noted in the paper,
there is considerable controversy about cheese, low-fat
milk and butter, as well as unprocessed red meat and
their relationship to cardiometabolic health.
Furthermore, for whole milk, there is insufficient evidence for
Public confusion about nutrition research and resultant
dietary fat recommendations
As a case-study, the science on dietary fat and
cardiovascular disease is complicated, therefore research
communications and dietary recommendations should be made that
accurately interpret the complexity of the evidence. When
asked about information provided by governments, experts,
food companies, and the media regarding the role of fats in
a healthful diet, 64% of consumers were confused and felt
that the information provided was contradictory [
term fat is particularly confusing because 90% of survey
respondents associate something negative with fat [
people, especially women, associate fat intake with obesity
while older men are more likely to associate it with heart
]. In a recent poll of Americans, nearly 70%
believed they should limit their fat intake to control their
weight and reduce their risk of heart disease [
results suggest that most consumers believe that their fat
intake should be as low as possible and that fat is not
needed for a healthy diet [
]. Despite consumer
perceptions, research supports the use of higher-fat diets such as
Mediterranean-style diets for weight loss and reducing
CVD risk [
]. Indeed, excess consumption of calories
has greater effects on weight and energy balance than the
amount and type of fat consumed [
While the public is very aware of total dietary fat, they
do not have a good understanding of the importance of
Fig. 4 Meta-analyses of foods and coronary heart disease, stroke, and diabetes mellitus. BMI indicates body mass index; CHD, coronary heart
disease; CI, confidence interval; CVD, cardiovascular disease; PC, prospective cohort; RCT, randomized clinical trial; and RR, relative risk. Adapted
with permission from Circulation [
fat quality or of the different sources of dietary fat. Pizza,
grain-based desserts, and chicken and chicken mixed
dishes are among the tops sources of various fats in the
diet of the U.S. population as seen in Table 2 [
reflects high levels of consumption of these items by
consumers. When asked about whole food sources of
fat, 3 out of 4 consumers identified olive oil and fish oil
as being healthful [
]. However, only 1 in 2 consumers
identified avocados and nuts as healthy source of fat
]. When consumers were asked the same question
using the terms monounsaturated fatty acids and
polyunsaturated fatty acids, only 16% believed they were
aBased on data from National Health and Nutrition Examination Survey 2005–2006 and analysis by the National Cancer Institute [
EPA eicosapentaenoic acid, DHA docosahexaenoic acid, MUFA monounsaturated fatty acids, PUFA polyunsaturated fatty acids
healthful, illustrating how the chemistry terms for
categorizing fats do not resonate with consumers .
For prevention of chronic diseases, nutrient-based
recommendations are more difficult to translate to the
public. Few individuals can accurately estimate their daily
calorie consumption, much less their intake of total fat
or specific fatty acids [
]. Interestingly, while 67% of
consumers are trying to limit their fat intake, few are
aware of how much fat they should actually be eating
. Only 22% of consumers correctly identified the
recommended range of calories from fat [
]. Sixty percent
of consumers believed that fat intake should be less than
14% of daily calories [
]. These results illustrate how
single-nutrient-based targets can quickly become
confusing to the average consumer. Based on the new
science for benefits of fats, in particular healthful
plant and seafood sources, and the harms of refined
starches and added sugars, many scientists have called
for the abandonment of the 35% limit on total fat
which has been eliminated in the 2015 Dietary
Guidelines (14) [
]. Consistent with this, the large
Women’s Health Initiative trial demonstrated no
benefits of lowering total fat from 36 to 29% of energy
on risk for CVD, diabetes, or cancers; while the
OmniHeart and PREDIMED trials demonstrated
significant CVD and other benefits from increasing
healthful fats to greater than 35% of energy [
]. Based on the scientific evidence, consumers
should focus on overall dietary patterns and consume
healthful foods rich in healthy fats including nuts,
vegetable oils, other plant sources of fats, and
substitute these for unhealthful foods such as processed
meats and foods high in sodium, added sugars, or
refined carbohydrates. This may result in a total fat
intake that exceeds 35% of calories , but the
majority of the fats in such a dietary pattern would
be healthy fats. The 2015 Dietary Guidelines Advisory
Committee strongly supported this shift toward
focusing on foods and healthier dietary patterns, rather
than individual nutrients or limits on total dietary fat
How should scientists communicate about fat in
order to clear up the confusion? Simple, easily
understood messages focused on overall dietary patterns
and foods rather than single nutrients are important.
As dietary guidance is shifting away from total fat
reduction and instead emphasizing types of foods and
overall dietary patterns, we should stop using low-fat
terminology and instead talk about healthy foods.
“How to” messages should inform the public of
specific foods that are sources of “healthy fats”. Focusing
on total diet quality and food patterns provides easily
actionable messages for consumers rather than talking
about percentages of specific fats.
Consumer confusion about nutrition messages can
also result from conflicting headlines in the media,
for example related to insufficient subject expertise
by journalists; limited communication skills,
availability, or willingness to be interviewed of nutrition
scientists; or a need for eye-catching headlines in the
fast-paced world of modern media. While it is
crucial to present new studies in the context of the
existing body of evidence, limited media space and
consumer attention work against this. Indeed, new
studies rarely negate previous findings or alter
fundamental paradigms, but rather add new information
to what was known before [
]. It is the
responsibility of both scientists and the media to ensure that
new results are accurately reported in appropriate
When communicating science, the following tips
should be top of mind:
Condense complex information into convincing and
motivating messages, but keep them evidence-based.
Use language at the 6th–8th grade reading level that
is clear and easy to understand.
The best messages are actionable, easy to
implement, and easy to visualize.
Remember to put research findings in context
within the prevailing body of evidence and avoid
sensational headlines [
Work with reporters to make sure your comments
and quotes are correct.
Have a few (e.g. three) key messages that consumers
can remember and reinforce with a strong bottom
Specify practical dietary substitutions with a
“compared to what” approach rather than general
“eat more/less” [
In order to help the population achieve a healthy diet,
communication will be needed on multiple levels
including individual advice, media communication, and the
development of programs and services at institutions such
as schools, workplaces, and healthcare systems.
Dietary fat is a confusing concept for the public, with both
evolving science over time and areas of remaining
uncertainty in the scientific literature. The resulting
communication challenges are amplified by the complexities of
evidence related to isolated nutrients vs. types of foods vs.
overall dietary patterns. While each of these types of
concepts can inform evidence-based nutrition science, and
resulting dietary recommendations, they should not be
considered in isolation without considering the overall types
and quality of evidence. Indeed, reviewing the entirety of
evidence allows the drawing of more valid conclusions
regarding the health effects of certain classes of foods relative
to other dietary choices.
We have presented evidence that the types of foods
consumed and the overall dietary pattern followed are far more
important for reducing CVD risk than total fat. Also the
types of fat and carbohydrates – and more relevantly, the
types of foods supplying these nutrients – are more
important than the total amounts of fats and carbohydrates in the
diet. Healthful plant and seafood sources of
monounsaturated and polyunsaturated fats have important health
benefits in the context of a healthy dietary pattern. Future
dietary recommendations should focus on healthful dietary
patterns to help consumers identify and choose foods that
are good sources of healthy fats. Furthermore, dietary
recommendations need to consider and incorporate principles
for effective scientific communication as a top priority in
order to effectively convey evidence-based scientific
messages to the public.
CHD: Coronary heart disease; CVD: Cardiovascular disease;
DHA: Docosahexaenoic acid; EPA: Eicosapentaenoic acid; HDL-C: High
density lipoprotein cholesterol; LDL-C: Low density lipoprotein cholesterol;
MUFA: Monounsaturated fatty acids; PUFA: Polyunsaturated fatty acids
This article is a review of the symposium “A Healthy Approach to
Understanding Dietary Fat Consumption: Understanding the Science and
Taking Action to Clear Up Consumer Confusion” held 30 March 2015 at the
ASN Scientific Sessions and Annual Meeting at Experimental Biology 2015 in
Boston, MA. The symposium was sponsored by the Hass Avocado Board.
Availability of data and materials
AL was the major contributor in writing the manuscript. All authors read,
edited, and approved the final manuscript.
Ethics approval and consent to participate
Consent for publication
AGL received an honorarium from the Hass Avocado Board for writing and
editorial services. FBH, PMKE, DM, and KMZ received honoraria from the Hass
Avocado Board for participating in the symposium and manuscript
preparation. PMKE is a member of the Avocado Nutrition Science Advisory
Group. DM reports honoraria or consulting from Astra Zeneca, Acasti
Pharma, GOED, DSM, Haas Avocado Board, Nutrition Impact, Pollock
Communications, and Boston Heart Diagnostics; scientific advisory board,
Omada Health and Elysium Health; and chapter royalties from UpToDate.
NAF is an employee of the Hass Avocado Board.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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