Nuts - a healthy snack

What is a nut?

If we look at the botanical definition it is strict. Nuts are basically hard shelled fruits that do not split open when they are ripe. Under this definition, only nuts such as acorns, chestnuts, hazels and hickories would qualify as nuts. Other things we call nuts are generally oil containing seeds within a shell. Many of these are drupes (stonefruits) including almonds, cashews, pecans, pistachios and walnuts. These are a fleshy fruit containing a nut inside a shell

The term "tree nuts" is also sometimes used, and includes almonds, brazils, cashews, chestnuts, hazels, macademias, pecans, pine nuts, pistachis and walnuts. That is all the best known nuts barring peanuts. Some people are aware that peanuts are in fact a legume, like peas and beans, and not a nut at all. However, it is a wider definition that I will use for this article, in which I include both peanuts and pinenuts as well(1).

Almonds

The seed of prunus amygdalus var. dulcis. It is closely related (same genus) to the plum, peach, nectarine, cherry and apricot. Unfortunately eating the seeds of some of these fruits will not be so beneficial for your guts. Almonds contain the toxin, hydrogen cyanide and another variety of almond tree prunus amygdalus var. amara. produces dangerous amounts of cyanide. Cyanide capsules being the favoured way to commit suicide by high ranking Nazis in Germany at the end of WW2. Almonds are a drupe - a fleshy fruit containing a nut inside a shell. In fact, cut open the fruit looks a bit like a small avocado with the almond shell and its nut being the equivalent of the avocado nut.

Brazils

The seed of a tree from the Amazon rainforest. Famous for its high content of cancer preventing selenium. Despite its name more brazil nuts are harvested in Bolivia than in Brazil. Brazil nuts are unusual in that they are generally not grown on plantations, but are collected from pristine rainforest where they are pollinated by large bees. There is some evidence that consumption of 2-3 Brazil nuts daily can raise your anti-oxidant potential and is more effeicient than selenium supplementation(2).

Cashews

The seeds from a drupe that grows below a cashew apple on a tree originally from Brazil. There is one cashew tree in Brazil that is so large it covers and area of about 8,000 sq metres(3).

Hazels (Filberts)

The seeds from various species of the tree corylus, such as the common hazel, corylus avellana and the filbert corylus maximaHazels are used to produce praline and Nutella and are one of the few nuts that are botanically considered to be a true nut.

Macadamia

The seeds from the evergreen, macademia integrifolia are toxic to dogs. They originate from Australia and Indonesia. They are considered by some botanists to be drupes, like almonds and cashews.

Peanuts

The seeds of arachis hypogaea are technically from the legume (pea and bean family of plants). Peanuts are responsible for many of the nut allergies that effect up to 1-2% of the population(4). Also, like a number of other nuts, such as brazils, peanuts can be infected with the carcinogenic mold, aflatoxin. Peanuts are widely used in the nut butter, peanut butter.

Pecan

The seeds from a type of hickory nut, carya illinoinensis. Unlike most hickory nuts which fit the strict botanical definition of a nut, the pecan is actually a drupe (stonefruit) like the almond. Pecans originate from Mexico and the United States.

Pinenuts

The seeds from certain pine trees, in particular pinus koraiensis, pinus gerardiana and in Europe the stone pine, pinus pinea. This nut (or seed) is a little different from most in that it is found in the cone of the pine trees. It is used extensively to make pesto sauce. 

Pistachios

The seeds of pistacia vera are small yellow-green coloured nuts that are commonly used as an ice cream flavouring. Like almonds, the pistachio is from a drupe - a fleshy fruit containing a nut inside a shell. Like poison ivy, the pistachio can contain urushiol, a skin irritant. However, the amount is small and so this is rarely a problem.

Walnuts

The seeds from juglans regia are known as English or Persian walnuts. The black walnut from juglans nigra is also edible. Walnuts are susceptible to insect and mold infestations. Molds can cause aflatoxin poisoning and any walnuts with this should not be eaten.

Nutrition in a nutshell

NUTRIENTSrdaAlmondsBrazilsCashewsHazelsPeanutsPecanPistachiosWalnuts
***** in g         
Protein 21.214.318.21525.89.220.615.2
Fat 49.466.443.860.749.27244.465.2
  sat 3.715.17.84.56.86.25.46.1
  mono 30.924.623.845.724.440.823.38.9
  poly w6 1220.67.87.915.620.613.238.1
  poly w3 0.010.020.060.090.00310.39.1
Carbohydrate 21.712.332.716.716.1142813.7
  fibre 12.27.53.39.78.59.610.36.7
Water 7.775.37.68.94.875.9
  100100100100100100100100
***** in mg         
Vitamin E1526.25.70.9158.31.42.30.7
Vitamin K0.1000.030.0200.00400.003
Vitamin B11.2000.40.60.60.70.90.3
Vitamin B21.3100.10.10.10.10.20.2
Vitamin B3163.40.31.11.812.11.21.31.1
Vitamin B61.30.10.10.40.60.30.21.70.5
Folate0.40.050.020.030.010.20.020.050.01
Magnesium420268376292163168121121158
Zinc113.14.15.82.53.34.52.23.1
Calcium 120026416037114927010798
Phosphorus700484725593290376277490346
Potassium47007056596606807054101025441
Copper0.911.72.21.71.11.21.31.6
Iron83.72.46.74.74.62.54.22.9
Manganese2.32.31.21.76.21.94.51.23.4
Selenium0.060.0031.90.020.0020.0070.0040.0070.005
ANTI NUTRIENTS        
Phytic acid 1280 18661620   760

We can see from the above table which shows amounts of nutrients in 100g of nuts, that they contain a good amount of nutrition in a small amount of food. The standout points for me are that magnesium, that relaxes the digestive tract and arteries in your body, is available in large amounts from all nuts, especially brazils and cashews. Iron and copper which can be in short supply in endurance runners and menstruating women, are particularly high in cashews. One or two handfuls providing the daily requirement. Peanuts stand out as providing a days worth of vitamin B3 and folate, important for women trying to concieve. 

However, rather than worry about the specific nutritional characteristics of a particular nut, my advice is to consume a variety of nuts. They all have one strong point or another and in combination you provide yourself with a wide variety of nutrients.

Nuts and health?

Allergic reactions (Atopy):

Nut allergies tend to be lifelong, with only about 1 in 10 children outgrowing their nut allergy(5). If you are allergic to one nut then you are likely to also be allergic to other nuts. Testing can be done to find out which proteins in the nuts you are allergic to. Depending on the severity of your immune response you may be able to consume nut products in moderation or not at all.

Health benefits:

Nuts are touted as a healthy snack. This is because they contain a fair amount of healthy fats, some low GI carbohydrates and protein also. The composition of different types of nut varies considerably, but in general they are a complete food that contains all the major nutrients that you need. When it comes to vitamins and minerals nuts are a great source of a number of B vitamins, especially B2 and B6 as well as the minerals: selenium (Brazils), magnesium and zinc.

Nut toxins:

Nuts can contain unhealthy substances either due to natural contamination with a common fungus or from additives.

  • The mold, aspergillus flavus, produces the potent carcinogen, aflatoxin and can affect nuts that are not kept sufficiently dry. 
  • Many nuts are salted for flavour and the amount of salt used can be incredibly high. I advise my clients to avoid salted nuts as these can destabilize appetite, leading to excessive thirst and encouraging overconsumption of the nuts.
  • Some nuts, especially in the US are treated with fumigants such as Propylene Oxide and Methyl Bromide to prevent the growth of mold. The only problem with this is that these fumigant themselves are carcinogenic and teratogenic (damaging unborn babies) respectively.
  • Phytic acid is a significant component of some nuts and can reduce the absorption of some of the beneficial micronutrients. Minerals such as calcium, chromium, iron, magnesium, manganese and zinc can all be bound by phytic acid in the gut. As such, it could be a good idea to eat nuts in between meals where they won't limit absorption of these minerals from other foods(6).

References:

1) http://waynesword.palomar.edu/ecoph8.htm Some explanation of what types of nut are true nuts, drupes or legumes.

2) http://ajcn.nutrition.org/content/87/2/379.long Brazil nuts raise your anti-oxidant potential.

3) http://en.wikipedia.org/wiki/Maior_cajueiro_do_mundo Biggest tree in the world?

4) http://www.inspection.gc.ca/food/chemical-residues-microbiology/chemical-residues/aflatoxins/eng/1347377061474/1347377332021 Aflatoxin levels in nuts.

5) http://www.ncbi.nlm.nih.gov/pubmed/14657884 prevalence of nut allergies in the US

6) http://www.marksdailyapple.com/nuts-and-phytic-acid/#axzz2K8zV2UFP Phytic acid in nuts