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Nuts: source of energy and macronutrients
Gemma Brufau, Josep Boatella and Magda Rafecas*
Nutrition and Food Science Department – CeRTA, University of Barcelona, 08028 Barcelona, Spain
On the basis of the high fat content of nuts, they are traditionally considered as foods that provide a high amount of energy. However, epidemio-
logic and clinical observations do not indicate an association between nut intake and increased BMI. There is a notorious variability in macro-
nutrient composition among nuts, although they have some consistent patterns. Nuts contain all major macronutrients: protein, carbohydrate,
and fat. The total protein content is relatively high, which makes them a good source of plant protein (especially for vegetarians). Although
nuts contain low amounts of some essential amino acids, this is not a nutritional concern due to the complement of protein. In addition, nuts
have a low lysine:arginine ratio, which is inversely associated with the risk of developing hypercholesterolemia and atherosclerosis. Carbohydrates
are the second highest macronutrient in nuts in terms of total calories provided. The fat fraction is characterized by a high amount of unsaturated
fatty acids and a low content of saturated fatty acids. In conclusion, the high content in unsaturated fatty acids, the low lysine:arginine ratio, and
the presence of other bioactive molecules (such as fibre, phytosterols, vitamin and other antioxidants, and minerals) make the addition of nuts to
healthy diets a useful tool for the prevention of cardiovascular heart diseases.
As we define them today, tree nuts (almonds, Brazil nuts,
cashew, hazelnuts, macadamia nuts, pecans, pine nuts, pista-
chios and walnuts) originate from Anatolia. From there, the
cultivation of tree nuts was introduced in Greece, then in
Italy during the Roman Empire, and finally it was extended
to all of Europe during the Middle Ages. The growing of
tree nuts was introduced in America in the 16th century
(Lemoine, 1998). Nuts are part of the Mediterranean diet,
although their per capita consumption is relatively low
(2–9 kg/year). Traditional Mediterranean nuts include
almonds, hazelnuts, walnuts, peanuts and pistachios. Typically
in Mediterranean diets, nuts are incorporated into many
dishes, such as snacks (roasted and salted almonds, hazelnuts,
and pistachios), sauces (‘romesco’ and ‘pesto’), cold soups,
such as ‘ajoblanco’ in Spain, cakes, pastries, and cookies
(‘turro
´
n’, ‘nougat’, walnut cakes, ‘menjar blanc’, ‘amaretti’).
Because of their high-energy content, nuts have been intro-
duced into sports snacks and supplements.
With today’s busy lifestyles, nuts are a convenient, tasty
and easy snack that contributes to a healthy lifestyle. In
addition to their tastiness, tree nuts and peanuts are both
cholesterol-free and rich in important nutrients, including veg-
etable protein, fibre and unsaturated fatty acids. They also con-
tain relevant micronutrients, such as folic acid, niacin and
vitamins E and B
6
, and minerals such as magnesium,
copper, zinc, selenium, phosphorus and potassium.
Nuts are part of the US Food Guide Pyramid and Mediter-
ranean Diet Pyramids. Experts recommend eating a variety of
foods from the five food groups every day in order to obtain
the nutrients you need. Nuts fall into the ‘Meat, Poultry,
Fish, Dry Beans, Eggs and Nut Group’ and can be eaten
every day. The recommended number of servings from this
group is 2– 3 per day. One-third of a cup of nuts or two
tablespoons of peanut butter contain the same energy as a
one-ounce serving of cooked lean meat.
Nuts also have a low water content, with water activity (a
w
)
between 0·6 and 0·7. While the low water content of nut helps
to preserve them for long periods of time, the high unsaturated
fat content increases their chances of becoming rancid,
especially during roasting, and this leads to a loss of flavour
during storage.
Since nuts are high in fat and therefore energy-dense, con-
sumers regard them as fattening foods. However, while they
are rich in energy they are also rich in many healthful nutri-
ents such as unsaturated fatty acids, vitamins, minerals, and
non-nutrients such as phytosterols and a host of phytochem-
icals that have health promoting benefits to humans.
Energy
Table 1 shows the total energy content of nuts. Brazil nuts,
pecans, and macadamia nuts are richest in fat and energy, fol-
lowed by almonds, walnuts, hazelnuts and pine nuts. Pista-
chios and cashews are the nuts with the lowest energy content.
According to the energy density (ratio between energy con-
tent in kcal and weight), foods can be classified into four
groups: a) very low energy density foods (, 0·6 kcal/g); b)
low energy density foods (0·6–1·5 kcal/g); c) medium
energy density foods (1·5–4 kcal/g), and d) high energy den-
sity foods (. 4 kcal/g). Nuts are high energy density foods
and their consumption could contribute to a high energy
intake and weight gain. The explanation for the excess con-
sumption of fat could be the fact that sensory-specific satiety
has been shown to be affected by the amount of food rather
than the energy content (Rolls et al. 1999).
* Corresponding author: Magda Rafecas, fax number þ 34-934035931, email magdarafecas@ub.edu
However, as discussed by Rajaram & Sabate
´
(2006) in this
supplement, available data suggest that adding nuts to the
habitual diets of free-living individuals does not induce
weight gain and may even help lose weight. Garcia-Lorda
et al. (2003) and Sabate
´
(2003) suggest several hypotheses
which may explain this fact. First, the absorption of energy
from nuts is incomplete, probably due to the structure of
lipid-storing granules with incomplete release of fatty acids
during digestion (Ellis et al. 2004), or to various fibre com-
ponents. Second, it is suggested that nuts exert a satiating
effect due to components such as fibre, whose role in energy
intake has been discussed at length (Marlett et al. 2002).
Third, nuts may increase resting energy expenditure and
diet-induced thermogenesis because of their high-protein con-
tent and high polyunsaturated-to-saturated-fatty acid ratio
(Jones et al. 1992), and this may result in less fat deposition.
When nuts are roasted with oil, there is an increase in their
total energy content (Table 1). Because of oil absorption, total
energy increases by an average of 30–40 kcal/100 g in oil-
roasted nuts. The nutritional value of the final product is
linked to the quality of the oil used and to the technological
treatment employed. Both factors can modify the fatty acid
profile of nuts.
Protein
The total protein content of some nuts is relatively high,
making them a good source of plant protein (Table 2). Pea-
nuts, walnuts, almonds, pistachios and cashews have the high-
est protein content, followed by Brazil nuts, hazelnuts and
pine nuts. Pecans and macadamia nuts have the lowest protein
content. The protein fraction decreases in roasted nuts due to
the increase in the fat content.
Even though the total amount of protein in nuts is high, the
biological value of nuts is not very high since they are limiting
in some essential amino acids. The amino acid composition of
walnuts and hazelnuts are compared to that of a whole egg in
Figs. 1 and 2. In general, for all nuts, threonine is the limiting
amino acid. Threonine is present in nuts in the range of
25–40 mg/g of protein compared to 44 mg/g of protein in a
whole egg. Brazil nuts are poorest and cashews are richest
in threonine. The tryptophan content of all nuts is quite similar
and close to that of whole eggs, with the exception of
macadamia nuts, which have less tryptophan (around 8 mg/g
of protein) than other nuts. Nuts are low in isoleucine, with
a content ranging between 32 and 40 mg/g of protein. This
contrasts with the total isoleucine content of whole egg of
54 mg/g of protein. For this amino acid, almonds show the
least amount (32 mg/g of protein) and cashews the most
(43 mg/g of protein). The total amount of leucine is almost
similar to that of whole eggs, around 86 mg/g of protein. Pis-
tachios and pecans have the lowest content of leucine, around
65 mg/g of protein.
As shown in Table 3, the dibasic amino acid lysine, which
is in deficit in many foods, is also poor in most nuts and con-
siderably lower than in whole eggs (70 mg/g of protein). The
sulphur amino acids, such as methionine and cysteine, are also
found in low amounts in nut protein. The exception is Brazil
nuts, which contain 96 mg/g of protein of total sulphur
amino acids, an amount higher than in whole eggs (57 mg/g
of protein). Other amino acids such as phenylalanine and tyro-
sine are present in significant amounts in the protein of all
nuts. The content of valine is quite important. Quantitatively,
cashew nuts provide 60 mg/g of protein, whereas whole eggs
provide 68 mg/g of protein. Almonds provide the lowest
total amount of valine, with a content of 38 mg/g of protein.
Finally, the content of histidine is quite high for nuts overall,
pistachios being the only nuts having a lower amount (21 mg/g
of protein) than whole eggs (24 mg/g of protein).
Table 1. Energy content of nuts
Raw Roasted
Energy
(kcal)
Energy
(kJ)
Energy
(kcal)
Energy
(kJ)
Almonds 581 2·431 607 2·541
Brazil nuts 656 2·743 – –
Cashew nuts 553 2·314 574 2·402
Hazelnuts 629 2·630 646 2·703
Macadamia nuts 718 3·004 718 3·005
Pecans 691 2·889 715 2·990
Peanuts 567 2·374 581 2·431
Pine nuts 629 2·632 – –
Pistachios 557 2·332 568 2·376
Walnuts 618 2·584 – –
Source: US Department of Agriculture Nutrient Data Base at http://www.nal.usda.
gov/fnic/cgi-bin/nut_search.pl
Fig. 1. Essential amino acids (mg/g protein) of walnut protein compared with
egg protein. B, Walnuts; r, Egg.
Table 2. Carbohydrate (CHO), protein, and fat content of nuts (g/100 g
of raw and roasted product)
Raw Roasted
CHO* Protein Fat CHO* Protein Fat
Almonds 19·9 21·9 50·6 17·7 21·2 55·2
Brazil nuts 12·3 14·3 66·4 – – –
Cashews 30·2 18·2 46·4 29·9 16·8 47·8
Hazelnuts 17·0 13·7 60·8 17·6 15·0 62·4
Macadamia nuts 13·8 7·9 75·8 13·4 7·8 76·1
Pecans 13·9 9·2 72·0 13·0 9·2 75·2
Peanuts 16·1 25·8 49·2 18·9 26·4 49·3
Pine nuts 19·3 11·6 61·0 – – –
Pistachios 28·0 20·6 44·4 26·8 21·4 46·0
Walnuts 9·9 26·1 65·2 – – –
* By difference (total energy minus energy from fat and protein).
Source: US Department of Agriculture Nutrient Data Base at http://www.nal.usda.
gov/fnic/cgi-bin/nut_search.pl
Looking at the amino acid composition of nuts, it can be
said that their protein profile is suboptimal because one or
more essential amino acids are present in small amounts.
Therefore, for the body to make good use of proteins, nuts
need to complement other food proteins. Strict vegetarian
diets that are rich in nuts can be supplemented with pulses
or other vegetables and with dairy products in order to provide
a high protein value.
The protein and amino acid content of nuts also varies
depending on the different cultivars. Savage (2001) found
some differences in the total protein content of walnuts from
various New Zealand cultivars. Another example of the differ-
ential protein content of walnuts is that the European commer-
cial cultivar G139 shows the highest protein content (16·8 g/
100 g), while the US Tehana cultivar shows the lowest protein
content (13·6 g/100 g).
Intake of plant protein has been associated with a low car-
diovascular risk compared to that of animal protein. Part of the
explanation for this association may be the lysine to arginine
ratio of plant protein (Kritchevsky, 1990). In general, veg-
etable proteins such as those in nuts are rich in arginine and
poor in lysine, whereas the opposite occurs in meat and
dairy products. The risk of developing hypercholesterolaemia
and atherosclerosis is higher with foods that have a high
lysine:arginine ratio (Carroll & Hamilton, 1975; Kritchevsky
et al. 1982; Sugano et al. 1984; Kritchevsky, 1990).
Arginine is the precursor of nitric oxide (NO), an endogenous
vasodilator and an important mediator of homeostatic processes
and host defense mechanisms (Moncada & Higgs, 1993; Faxon
et al. 2004). Arginine is required by the constitutive enzyme
endothelial NO synthase to produce NO. Administration of
this amino acid improves endothelial function in animal
models and in humans with hypercholesterolemia and athero-
sclerosis (Gornik & Creager, 2004). It has been hypothesized
that the decreased coronary heart disease risk observed in associ-
ation with frequent nut intake in epidemiological studies,
reviewed by Kelly & Sabate
´
(2006) in this supplement, may
be due in part to the high arginine content of nuts leading to
enhanced synthesis of NO (Cooke et al. 1993; Feldman,
2002). The lysine:arginine ratio of nuts is quite low. Hazelnuts,
pine nuts and walnuts have the lowest ratios (0·19–0·20);
pecans, Brazil nuts and almonds have ratios of 0·23–0·24, and
the highest ratios are found in pistachios and cashews (< 0·5)
(Souci et al. 2000). Such ratios are much lower than those pre-
sent in animal proteins such as casein (1·9) and whole milk
(2·4), and even in soy protein (0·58–1·0) (Kritchevsy et al.
1982). Thus, nut protein has a lysine:arginine ratio that is poten-
tially more beneficial than that of soy protein.
The insulin:glucagon ratio has been used as an early metabolic
index of the effect of dietary proteins on serum cholesterol
levels, a risk factor for cardiovascular diseases (Sanchez & Hub-
bard, 1991). Therefore, taking into account that plant proteins
(such as those contained in soy and nuts) are richer in arginine
and glycine than animal proteins (such as casein), and that the
postprandial insulin:glucagon ratio is affected by postprandial
plasma amino acids (Sanchez et al. 1988; Calbet & MacLean,
2002), it is suggested that foods rich in protein (such as nuts),
with a high content in arginine and glycine, may reduce the
risk of chronic degenerative diseases by their influence on insu-
lin and glucagon levels (Hubbard et al. 1989; Krajcovicova-
Kudlackova et al. 2005).
Carbohydrate
The total carbohydrate content of nuts is provided in Table 2.
The lowest amounts are found in walnuts, and progressively
increasing amounts occur in Brazil nuts, pecans and Macada-
mia nuts, almonds and pine nuts, pistachios and, finally, cash-
ews. Different composition tables, however, may show
different amounts of carbohydrate for specific nuts depending
on whether the carbohydrate content has been actually deter-
mined or calculated.
Recent data (Luscombe et al. 2002, 2003; Layman et al.
2003) suggest that some undesirable effects of low-carbo-
hydrate diet may be counteracted by a higher protein intake,
as high protein diets have been shown to induce favourable
effects of feelings on satiety and hunger, help preserve lean
body mass, effectively reduce fat mass and beneficially
impact on insulin sensitivity and the blood lipid status. There-
fore, the nutritional composition of nuts, rich in protein and
low in CHO, make them a suitable food for incorporating
into diets intended for weight loss and weight control
(Adam-Perrot et al. 2006).
Fat
Total fat is the main fraction in nuts. As shown in Table 2, the
total fat content per 100 g ranges from 44·4 g in pistachios to
75·8 g in macadamia nuts. Again, the geographic origin of
Fig. 2. Essential amino acids (mg/g protein) in hazelnut protein compared
with egg protein. B, Hazelnuts; r, Egg.
Table 3. Argini ne and lysine content (g/100 g of protein)
and their ratio in nuts
Arginine Lysine Lys:Arg ratio
Almonds 116·0 28·3 0·24
Brazil nuts 150·0 35·4 0·23
Cashews 116·5 50·9 0·44
Hazelnuts 147·9 28·1 0·19
Macadamia nuts 177·2 22·8 0·13
Pecans 128·4 31·3 0·24
Peanuts 119·6 35·9 0·30
Pine nuts 194·6 37·5 0·19
Pistachios 82·4 46·8 0·57
Walnuts 150·4 29·6 0·20
Source: US Department of Agriculture Nutrient Data Base at http://
www.nal.usda.gov/fnic/cgi-bin/nut_search.pl
different tree nut cultivars can result in variations of fat con-
tent. Parcerisa et al. (1993) studied Spanish hazelnut varieties,
such as ‘Pauetet’, ‘Gironell’ and ‘Negret’, and reported that
the geographic origin and the climatic conditions modified
the fat content. For instance, for the ‘Negret’ variety, the
authors showed a difference of 8 % in fat content depending
on location, even within the same geographical area (Reus
or Falset in Tarragona, Spain). This variability affects fatty
acid composition as well, especially the proportions of oleic
and linoleic acids. Triacylglycerol content, especially triolein,
and vitamin E and mineral content are also affected by
variety and geography. This variability may cause changes
in the stability of nuts, especially during storage. On the
other hand, the technological treatment applied to nuts can
also modify the lipid content and the fatty acid composition.
As discussed, oil roasting increases the fat content by approxi-
mately 4 %, due to dehydration occurring during the procedure
and both adsorption and absorption of oil used for roasting.
This is important because it may change the nutritional
value of the lipid fraction of nuts, and special attention must
be paid to the quality of the oil used in the roasting and
frying processes.
The favourable fatty acid composition of nuts is discussed
in detail by Ros & Mataix (2006) in this supplement. Nuts
are characterized by a high content of MUFA and PUFA,
and proportionally, less SFA. The predominant type of unsatu-
rated fatty acid in most nuts is MUFA, contributing on average
62 % of the energy from fat. Together, MUFA and PUFA con-
tibute around 91 % of the energy from fat (Kris-Etherton et al.
1999). Parcerisa et al. (1998) studied different varieties of
hazelnuts from Oregon, and found relevant difference in
fatty acid composition. For instance, the content of PUFA in
that study ranged from 8·7 % in the Italian variety ‘Tonda
Romana’ to 18 % for the Turkish variety ‘Tomboul’.
A large number of studies (Sabate
´
1993, 1999; de Lorgeril
et al. 1999, 2001) suggest that nuts may play an important role
in reducing the risk for cardiovascular diseases. In one study
(Albert et al. 2002), researchers found that, although the ben-
efits were greatest for frequent nut eaters, those who ate nuts
even twice a week had a 47 % lower risk of sudden cardiac
death and a 30 % lower risk of total coronary heart disease
than those who rarely or never consumed nuts. Nuts, particu-
larly walnuts, contain n-3 fatty acids, which have been shown
to elicit cardioprotective effects due in part to reduced platelet
aggregation and vasoconstriction (Kaminski et al. 1993) and
favourable effects on blood coagulation via fibrinolysis
(Barcelli et al. 1985) and blood clot formation (Shahar et al.
1993).
In the summer of 2004, the FDA accepted a qualified health
claim for nuts and nut-containing products because of the link
of nut consumption with a reduced risk of heart disease. The
nut products which meet the FDA’s criteria may be labelled
as follows: ‘Scientific evidence suggests but does not prove
that eating 1·5 ounces per day of most nuts as part of a diet
low in saturated fat and cholesterol may reduce the risk of
heart disease’.
In addition to the distinctive fatty acid profile of nuts, they
are good sources of several other important nutrients. Nuts are
a source of phytosterols and other phytochemicals, including
ellagic acid, flavonoids, phenolic compounds, luteolin and
tocotrienols. Other micronutrients present in notable quantities
in most nuts include thiamine, niacin, riboflavin, selenium,
potassium and iron. Therefore, the constituents of nuts may
contribute to their beneficial health effects through several
mechanisms.
Acknowledgements
The authors would like to thank the important help and advice
given by Dr Jordi Salas-Salvado
´
(Unitat de Nutricio
´
Humana,
Facultat de Medicina de Reus, Universitat Rovira i Virgili),
and from Nucis Foundation Health and Tree Nuts.
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