Can eating pistachios be good or bad for you?

Eating pistachios could be healthy because they:

• are a good nutrition source of calories, protein and unsaturated fats
• contain insoluble fiber, which helps to prevent constipation
• can decrease blood cholesterol levels

Possible dangers (rare):

• Allergic reaction
• Aflatoxin
• Salmonella

Picture 1. Pistachios
(source: Dreamstime, CC license)

Chart 1. Nutritional value of pistachios (serving size: 1 oz = 28 grams = 1 handful = 49 dry roasted kernels without shells) 4,13
NUTRIENT	AMOUNT	DAILY VALUE (DV) (%)
Water	0.6 g
FATS 4,6,13,62,70	13 g	20%
-Saturated	2 g	8%
— palmitic acid (-10% fats)
— stearic acid (-3% fats)
-Monounsaturated	7 g
— oleic acid (50-70% fats)
-Polyunsaturated	4 g
— omega 3: alpha-linolenic (ALA) (0.2-0.6% fats)	74 mg
— omega 6: linoleic acid (LA) (15-35% fats)	4 g
–Trans fats	0 g
Cholesterol	0 g
CARBOHYDRATES	8 g	3%
-dietary fiber	3 g	12%
–insoluble	g
–soluble	g
-sugars	2 g
PROTEINS	6 g	12%
VITAMINS
Vitamin B1 (thiamin)	0.2 mg	16%
Vitamin B6 (pyridoxine)	0.6 mg	18%
MINERALS
Copper	0.4 mg	19%
Iron	1.2 mg	7%
Magnesium	34 mg	8%
Manganese	0.4 mg	18%
Phosphorus	137 mg	14%
Potassium	300 mg	8%
Sodium	114-220 mg	5-10%
OTHER NUTRIENTS
Coenzyme Q10 47	0.6 mg
Lutein and zeaxanthin (carotenoids) 48,70	0.3-1.4 mg
Phytosterols	60 mg

Calories in Pistachios

1 oz (28 g = 1 handful) of pistachio kernels without shells contains 160 Calories ²⁴. This is less than most other nuts, which contain about 170-200 Calories per oz.(

Pistachios and Weight Loss: Are pistachios fattening?

One ounce of dry roasted pistachio kernels contains 160 Calories, which is about 6% of the daily calorie needs for a moderately active adult (2,500 Calories) ⁴. Many people say eating pistachios is addictive and they may eat several ounces in one sitting, which may be fattening.

On the other hand, pistachios in shells slow down the eating process, so people usually eat less in-shell pistachios than the shelled pistachios or other shelled nuts (“pistachio principle”) ⁸¹. In one weight-loss study lasting for 12 weeks, participants who ate 2 oz pistachios daily with their regular diet lost more weight than those who ate 2 oz pretzels ³⁴. In one study in Chinese adults with metabolic syndrome (obesity, increased triglyceride and glucose levels and high blood pressure), consuming 1.5-2.5 oz pistachios daily along with a low-fat diet for 12 weeks did not result in weight gain compared with individuals on the control diet with no pistachios ⁷⁶. Some other studies have also revealed a favorable effect of consuming pistachios on weight loss ³⁵.

Unsalted and Salted Pistachios

Unsalted pistachios contain 3 mg sodium per ounce (28 g), which is 0.1% Daily Value (which is 2.4 grams sodium per day) ^5,43, and 0,2% of the American Heart Association (AHA) recommended daily limit (which is 1.5 grams sodium per day) ⁴². Salted pistachios may contain 125-220 mg sodium per ounce (28 g), which is 5-10% Daily Value (data from nutrient labels and references ^4,43), and 8-15% of the AHA daily limit ⁴².

Antioxidants

Pistachios are often mentioned as a rich source of antioxidants, but 1 oz of dry roasted pistachios contains only a low amount of them:

• 0.3 mg lutein and zeaxanthin (1/2 cup of spinach contains 15 mg) ⁴⁹. Studies made so far have found no clear benefits of lutein supplements (in doses up to 70 x as large as in 1 oz pistachios) for human eye health ^64,65,67. Lutein intake was associated with decreased risk of age-related macular degeneration (AMD) ⁶⁶.
• 74 IU vitamin A (1% Daily Value)
• 45 mcg beta-carotene (1/2 cup of boiled kale contains 5,000 mcg) ⁵⁰
• 0.6 mg vitamin C  (1% DV)
• 0.5 mg vitamin E (3% DV)
• 2.6 mcg selenium (4% DV)
• See also references 4 and 14

Roasting of pistachios can decrease the antioxidant activity by 60% ¹⁴.

Polyphenols

Polyphenols act as antioxidants in laboratory tests, but it is not clear if they also act as antioxidants in the human body ¹⁷. In two laboratory studies (not in humans), pistachio extract had anti-inflammatory ¹⁵ and antibacterial effect ¹⁶. Main polyphenols in pistachios ¹⁴:

• Resveratrol ^54,55
• Proanthocyanidin
• Isoflavones daidzein (3.68 mg/100 g) and genistein (3.40 mg/100 g) ¹⁴

Constipation Prevention

Pistachios contain about 3 g of fiber, mostly insoluble fiber, per ounce (see Chart 1 and Reference 22). Pistachios are often included in the lists of recommended foods to prevent constipation ²⁶, but they themselves can cause constipation if not consumed with sufficient amount of water ²⁰. Fiber is also prebiotic — it promotes the growth of healthy bacteria in the colon ³⁸.

Blood Cholesterol Levels and Heart Disease

In short:

1. One ounce of pistachios contains only 60 mg phytosterols (see Chart 1). Phytosterols may lower blood cholesterol, but according to one estimation, consuming 1-2 grams phytosterols (17-35 oz pistachios) per day would be needed to reduce blood cholesterol levels ^51,52.
2. In various small and short-term (4 weeks) studies, adding 2-4 ounces of pistachios to a low-fat diet resulted in a drop of blood total and LDL cholesterol levels (risk factors for coronary heart disease) by about 10% ^7,8,72.
3. So far, there is no direct proof that eating pistachios helps to prevent heart disease. According to the U.S. Food and Drug Administration (FDA): “Scientific evidence suggests but does not prove that eating 1.5 ounces per day of most nuts [including pistachios], as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.” ³

Antioxidants and Cholesterol

In one 2010 study lasting for 4 weeks, in 28 individuals with slightly elevated blood cholesterol levels, pistachios increased blood levels of antioxidants beta-carotene (precursor of vitamin A) by 30%, gamma-tocopherol (vitamin E) by 15% and lutein by 85%, and decreased the levels of oxidized LDL-cholesterol by 10-15% compared to a low-fat control diet without pistachios ⁸. Oxidized LDL-cholesterol supposedly promotes atherosclerosis (artery hardening), so decreased oxidized LDL-cholesterol levels might help to prevent atherosclerosis ⁸. The actual health benefits of antioxidants in preventing heart disease were disappointing so far, according to professor Penny Kris-Etherton, one of the authors of the study ⁹.

Potassium and Blood Pressure

According to the review of studies published in Nutrient Evidence Library (by USDA – the US Department of Agriculture), pistachio nuts as a part of a healthy diet have “a favorable impact on cardiovascular risk factors, particularly serum lipid levels, and possibly on blood pressure.” ²⁹

Diabetes Mellitus

Pistachios are often included in the lists of appropriate foods for diabetics ³⁹ for the following reasons:

• Low glycemic index ⁷⁹:
  • 1 oz pistachios = ~6
  • 2 oz = ~4
  • 3 oz = ~9
  • In one small study in 10 healthy adults, the addition of 2 ounces of pistachios decreased glycemic index (GI) of parboiled rice (from 73 to 59) and pasta (from 95 to 56) ⁷⁹.
• Adding 1-2 oz pistachios daily to the diet usually does not result in weight gain ^34,35,76.
• Adding 2-4 oz pistachios per day to the diet can reduce blood total and LDL cholesterol levels by about 10% ^7,8.

Cancer

In various laboratory studies, pistachios inhibited the growth of cancer cells ²⁵, but the actual preventative effect of pistachios on cancer growth in humans was not confirmed so far.

Erectile Dysfunction

In one small 2011 study in 17 married men with erectile dysfunction, consuming 100 grams pistachios per day for 3 weeks improved erectile function ¹. More studies are warranted to evaluate if this was a real pistachio effect or only a placebo effect.

Pistachio Allergy

Allergic reactions to pistachios are relatively rare ⁷⁵. They can occur in children and adults; they are usually lifelong and often severe ⁷⁵. Individuals allergic to pistachios may (or may not) be allergic to:

• Almonds, cashews and peanuts ⁷⁵ and possibly to other nuts and other members of the family Anacardiaceae, such as mango, poison ivy, oak and sumac, pepper tree, smoke tree.
• Foods that contain pistachio nuts or flavors derived from them, such as pistachio ice cream, cakes, mortadella, etc.
• Foods with “may contain traces of nuts” warnings on labels.
• Unrefined, “cold-pressed” pistachio or other nut oils
• Rarely, an individual with a pistachio allergy can be allergic to other foods not related to nuts in any way, such as fish, soy or eggs.
• Smelling pistachios, except when inhaling actual pistachio dust, does not likely cause an allergic reaction.
• Touching pistachios can cause a local skin reaction to individuals sensitive to urushiol, a type of oil in pistachios ^27,31.
• Kissing a person who has eaten pistachios may trigger an allergic reaction (usually mild) in a sensitive individual.

Individuals allergic to salicylates (aspirin) may also be allergic to pistachios, which contain small amounts of salicylates ³².

Symptoms of pistachio allergy typically appear within few minutes or, sometimes, hours, after ingesting pistachios, may last for several hours and may include:

• “Oral allergy syndrome” with itchy, tingling, burning or swelling of the mouth, lips, tongue and throat
• Hives with itchy skin, eyes, nose, sneezing, runny nose
• Abdominal pain, vomiting, diarrhea
• Severe allergic reaction (anaphylaxis) can include a cough, wheezing, difficulty breathing, swollen face, vomiting, fainting, shock (a severe drop of blood pressure) or, rarely, death.
• References ^41,77

Treatment

• Mild allergic reactions can be treated with oral antihistamines.
• Anyone with a severe allergy to pistachios should carry an epipen (an injecting device with epinephrine [adrenaline], which can prevent anaphylactic reaction) ⁷⁷.

Prognosis

Only 10% of children outgrow tree nut allergies ⁷⁷.

Prevention

Currently, it is not clear if the early introduction of pistachios or other nuts increases or decreases the risk of allergies in children. For a long time, doctors were advising mothers against offering nuts to children younger than 3 years, but some newer studies have not confirmed the association between the early introduction of nuts to children or maternal nuts ingestion during pregnancy or breastfeeding and allergies in children ^44,53. According to some studies, the early introduction (4-6 months of age) of tree nuts may even decrease the risk of allergies to nuts ^44,53, but at this point, the results of all these studies are far from conclusive.

Kidney Disease

Pistachios are relatively high in proteins, potassium and phosphorus ⁴. Doctors often recommend restriction of these nutrients to kidney patients ⁵⁸. It is your doctor who can tell if you may eat pistachios or not.

Kidney Stones

Pistachios contain a moderate amount of oxalates (10-25 mg per oz), and methionine (which is converted to cystine), so consumption of large amounts of pistachios may increase the risk of calcium oxalate and cystine kidney stones in susceptible individuals ^33,40.

Navel Orangeworm (NOW)

A navel orangeworm (NOW) is a cream-colored, orange or red, up to 1 inch (25 mm) long worm, that appears in the pistachio seed or between the seed and the shell along with webbing, frass and decayed nutmeat ⁴⁶. The worm itself is probably not harmful to human health, but pistachios infested by orangeworms are more likely contaminated with the Aspergillus fungi, which produce aflatoxin. A picture of an orangeworm in the pistachio.

Salmonella

Occasionally, raw pistachios are contaminated by the bacterium Salmonella, which can cause diarrhea and can be fatal for infants, elderly and individuals with weak immune system ⁶¹. Roasting is supposed to kill bacteria, but when roasting is not done correctly or when roasted pistachios get in contact with raw ones they may get contaminated ². Contamination with Salmonella does not change the pistachios’ look or smell ⁸³. No actual infection after consuming pistachios have been firmly proven in the United States so far ⁶¹. Refrigerating or freezing pistachios at -2.2 °F (-19 °C) does not kill bacteria ^59,83.

Toxicity

Organophosphorus insecticide guthion ²⁸ and other insecticides used to spray pistachio trees may be potentially harmful to human health, but probably more for people directly exposed to guthion (workers on a pistachio farms) than for the pistachio consumers ²⁸.

Acrylamides formed during roasting are carcinogenic for animals and are considered as “probable carcinogens” for humans ^18,96. The actual association between consuming roasted pistachios and cancer has not been proven so far.

Pistachios are relatively high in manganese. Individuals with a genetic disease “Dystonia/Parkinsonism, Hypermanganesemia, Polycythemia, and Chronic Liver Disease” should avoid pistachios and other high-manganese foods, such as sunflower seeds ⁵⁷.

Aflatoxin is a “known human carcinogen” ⁷³ produced by the fungus Aspergillus flavus, which can contaminate pistachios during growing or storing in moist or warm environment ^36,68,74. Long-term consumption of aflatoxin can cause cancer in animals and it was associated with hepatitis B and liver cancer in humans in South Asia and sub-Saharan Africa where aflatoxin intake is high ^11,63,74.

Currently, it is not known which amount of aflatoxin can cause liver cancer, and direct association between pistachio consumption and liver cancer has not been established so far ⁶⁹. Aspergillus fungi are not always visible to a naked eye but can be detected using the UV light ⁴⁵. Roasting can significantly, but not completely, reduce the amount of aflatoxin in pistachios ⁷¹. Risk factors for aflatoxin contamination include early pistachio nut splitting (July), infestation with orangeworm, high humidity and temperature during pistachio harvesting, transport or storage ¹¹.

Picture 2. Pistachio affected by fungi

Irritable Bowel Syndrome (IBS) and Diarrhea

Some people with IBS believe insoluble fiber in nuts can trigger diarrhea.

Hereditary Fructose Intolerance, Fructose Malabsorption, Low-FODMAP Diet

• Individuals with hereditary fructose intolerance (HFI) should avoid pistachios, which contain 36 mg fructose per oz ⁴.
• Individuals with fructose malabsorption usually do not need to avoid pistachios, because they contain more glucose than fructose (glucose helps to absorb fructose).
• Pistachios are relatively high in sugars (2g/oz), so they are not a part of the low-FODMAP diet (FODMAP = Fermentable Oligo-, Di-, Mono-[saccharides] And Polyols) ¹⁹.

When pistachios are stored for a prolonged time, they can become rancid — they smell and taste awful. Rancidification is due to:

1. Exposure of fats to water (air moisture), which results in the formation of free fatty acids, which by themselves are not harmful to health, but can smell ⁸³.
2. Exposure to oxygen, which results in oxidation of unsaturated fatty acids. This may result in the formation of free radicals, which, if consumed, can increase the risk of the artery hardening (atherosclerosis) and cancer ⁷⁸. Ingestion of rancid fats can trigger vomiting or diarrhea ⁷⁸.

Exposure to oxygen (air), water (air moisture), light and heat stimulates rancidification, so pistachios need to be stored in tightly enclosed containers or plastic bags with little air in them, in a dry, dark and cool place ⁶². Abovementioned factors can also deactivate antioxidants (vitamins and polyphenols) and chlorophyll (loss of green color) ⁶². After harvesting, metabolic processes in pistachios continue; the breakdown of fats in the presence of air and moisture can result in pistachios self-heating and spontaneous combustion ^45,60. Fat breakdown can also produce a significant amount of carbon dioxide (CO₂), which can build up to dangerous levels in a poorly ventilated store ⁴⁵.

Shelf life

• Fresh, non-dried pistachios may become rancid quickly (weeks).
• According to researchers from the University of California, both in-shell and shelled dry-roasted pistachios can be stored for up to 1 year in a refrigerator (at 39.2 °F or 4 °C) or up to 3 years in the freezer (0 °F or -18 °C) ⁸⁰.

Is it OK to eat closed pistachios?

Closed pistachios are unripe but edible. Do not crack open pistachios with teeth.

Are raw (fresh) pistachios edible?

Yes, fresh pistachios are edible and are available in some markets during the harvesting time (September). They appear enclosed in soft red or red-green-yellow hulls.

Is it safe to eat pistachios after their expiration date?

Pistachios become rancid with time and may catch mold, which can produce aflatoxins, so it may not be wise to eat expired pistachios.

Is it OK to eat pistachios before bed?

Pistachios are high in fat, which can stay in your stomach for an hour or two and thus maintain your digestive process active what may cause you to fall asleep later or decrease the quality of your sleep. Most doctors advise against eating before bed ³⁷.

Can pistachios trigger or prevent heartburn?

Fatty foods, which pistachios are, can trigger heartburn, especially in individuals with GERD (gastroesophageal reflux disease) ⁶. Some holistic health promoters say pistachios can prevent heartburn, but there seems to be no scientific evidence to support such recommendations.

Can eating pistachios make you sick?

Yes, if you are allergic to pistachios or if you eat rancid ones.

Is it safe to eat pistachios during pregnancy?

In general, there is probably no reason to avoid pistachios during pregnancy, except if you are allergic to them.

Are pistachios appropriate snack for kids?

Pistachios are not appropriate for small kids, who may put pistachio seeds or shells in their ears or noses or they may accidentally inhale nuts during eating.

Does eating pistachios increase the risk of gout?

There is no scientific evidence about pistachios as a risk factor for gout.

Are bleached pistachios harmful?

Bleaching pistachios probably does not cause any harm to human health ³⁰.

Summary: Are pistachios a healthy snack?

Pistachios added to carbohydrate meals lower glycemic response of meals, and regular pistachio consumption may reduce blood cholesterol levels. Still, it is not known, if eating pistachios has any actual beneficial effect on diabetes and heart disease. Pistachios seem to be a good source of proteins and can help to prevent constipation in some individuals.

Aflatoxin, acrylamide and Salmonella contamination of pistachios may be potentially dangerous for health but it is not clear if they actually caused any illness so far. Individuals with certain genetic diseases may need to avoid pistachios because of their fructose, manganese and oxalate content. Pistachio nuts are not appropriate for small children.

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