Tree nuts and the lipid profile: a review of clinical studies
Amy E. Griel and Penny M. Kris-Etherton*
The Pennsylvania State University, S-126 Henderson Building, University Park, PA 16802, USA
Tree nuts have a fatty acid profile that favourably affects blood lipids and lipoproteins. They are low in saturated fat and high in unsaturated fatty
acids and are rich sources of other nutrients. An extensive database consistently shows total and LDL cholesterol-lowering effects of diets low in
saturated fat and cholesterol and high in unsaturated fat provided by a variety of tree nuts. Collectively, a summary of studies conducted to date
shows that tree nuts reduce LDL cholesterol by 3–19% compared with Western and lower-fat diets. Nuts also contain many nutrients and bio-
active compounds that appear to contribute to the favourable effects on lipids and lipoproteins – these include plant sterols, dietary fibre and anti-
oxidants. Because of their unique nutrient profile, nuts can be part of a diet that features multiple heart-healthy foods resulting in a cholesterol
lowering response that surpasses that of cholesterol-lowering diets typically used to reduce CVD risk.
Tree nuts: Lipids: Lipoproteins: Clinical trials: Humans
Numerous clinical studies have been conducted to evaluate the
effects of nut consumption on lipids and lipoproteins, major
risk factors for cardiovascular disease (CVD) (reviewed by
Kris-Etherton et al. 2001; Mukuddem-Petersen et al. 2005).
The impetus for the clinical studies were the results of several
major epidemiologic studies that have demonstrated beneficial
effects of nut consumption on coronary disease risk (Fraser
et al. 1992; Fraser & Shavlik, 1997; Fraser et al. 1997; Hu
et al. 1998; Hu & Stampfer, 1999; Ellsworth et al. 2001;
Albert et al. 2002; Jiang et al. 2002). Importantly, these results
have been demonstrated consistently in all population groups
studied, including men and women of all ages, African-Amer-
icans and persons with diabetes. The clinical database for nuts
is increasing rapidly and the preponderance of evidence is on
lipid and lipoprotein endpoints as a means to explain
The clinical studies have assessed the effects of different tree
nuts, including walnuts, almonds, macadamia nuts, pecans, pis-
tachios and hazelnuts. Many experimental designs have been
employed with different population groups. For example,
studies have been conducted with free-living subjects on self-
selected diets who were given either specific instructions to
follow regarding nut consumption or daily allotments of nuts
in which subjects were fed known quantities of the target nut or
nut oil in a nutrient defined diet. The studies have varied with
respect to length, number of treatments, ‘dose’ of nut/nut oil,
as well as the endpoints measured. Typically, the studies have
been designed to test the hypothesis that the test diet with nuts
elicits a favourable lipid and lipoprotein response compared
with a Western diet and/or a lower fat diet that is recommended
for cholesterol lowering.
The studies to date have consistently shown that a nut/nut
oil-containing diet, low in saturated fat and cholesterol,
beneficially affects lipids and lipoproteins compared to the
control diet (typically either a low fat diet or an average
American/western diet). (Table 1) The favourable effects of
the nut/nut oil diet on the plasma lipid and lipoprotein profile
is a mechanism that appears to account for some of the cardio-
protective effects observed in the epidemiologic studies. The
purpose of this review is to examine the evidence on the
effects of tree nuts on established lipid and lipoprotein risk
factors, including total cholesterol (TC), LDL cholesterol
(LDL-C), HDL cholesterol (HDL-C), and triglycerides (TG).
In addition, the effects of nut consumption on more contem-
porary lipid/lipoprotein risk factors including non-HDL
cholesterol and the ratios of TC:HDL-C and LDL-C:HDL-C
will be reviewed. Since oxidative stress is a key event in ather-
ogenesis, and many studies have evaluated the effect of nut
consumption on LDL oxidation, this review will also examine
this literature. As will become evident, there is an impressive
database showing that tree nut consumption improves the lipid
CHD risk factor profile, which may explain the cardio-protec-
tive effects of nut consumption that have been demonstrated in
the epidemiologic studies.
Nuts have a unique nutrient profile that beneficially affects
lipids and lipoproteins. This is due largely to the favourable
fatty acid profile of nuts. Nuts are low in saturated fatty
acids and high in unsaturated fatty acids, including monounsa-
turated fatty acids, omega-6 and omega-3 fatty acids. In
addition, nuts are a source of dietary fibre; soluble fibre has
a blood cholesterol-lowering effect. Collectively, the fatty
acid profile and fibre content of nuts can markedly lower
LDL cholesterol. In fact, the cholesterol reduction observed
in clinical studies of nuts is approximately 25% greater than
would be expected based on blood cholesterol-predictive
equations (Table 2) (Kris-Etherton et al. 1999). Ten out of
seventeen controlled feeding studies in this review demon-
strate a decrease in LDL-C that is greater than that which
would be predictedusingblood cholesterol-predictive
*Corresponding author: Penny M. Kris-Etherton, fax 814 863 6020, email email@example.com
Table 1. Clinical studies evaluating the effects of tree nuts on lipids and lipoproteins
(A) Morgan et al. (2002)
Low-fat, low-cholesterol diet
Walnut supplemented diet
(B) Almario et al. (2001)
Habitual diet (HD)
HD þ Walnuts
Low-fat diet (LFD)
LFD þ Walnuts
(C) Sabate et al. (1993)
Step 1 diet
Step 1 diet þ Walnuts
(D) Ros et al. (2004)
(E) Zambon et al. (2000)
(F) Iwamoto et al. (2002)
(G) Chisholm et al. (1998)h
Low-fat diet (LFD)
LFD þ Walnuts
(H) Zhao et al. (2004)
‘Average American’ Diet
Walnut diet high in Linoleic Acid (LA)
Walnut diet high in a-Linolenic
(I, J) Abbey et al. (1994)
(K) Wien et al. (2003)
low-calorie formula-based diet
(L) Jenkins et al. (2002)
Self-selected low-fat diet (LFD)
LFD þ half-dose almond supplement
LFD þ full-dose almond supplement
(M) Hyson et al. (2002)
Whole almond diet
Almond oil diet
(N) Sabate et al. (2003)
Step 1 diet
(O) Lovejoy et al. (2002)
Low-fat control diet
Low-fat almond diet
High-fat control diet
High-fat almond diet
(P) Spiller et al. (2003)h
Roasted salted almonds
Roasted almond butter
(Q) Spiller et al. (1998)
Olive oil-based diet
(R) Garg et al. (2003)
(S) Colquhoun et al.
Low-fat, high-carbohydrate diet
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