In-Shell Pistachios Cut Calorie Intake by 41%, Studies Find

Author: Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 16 Jul 2011 - Updated: 5 Oct 2026
Publication Type: Informative

Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content

Synopsis

This research, drawn from two studies published in the peer-reviewed journal Appetite, looks at how eating pistachios still in their shells changes the amount people eat. In the first study, people given in-shell pistachios took in 41 percent fewer calories than those given shelled nuts, and in the second, leaving the empty shells in view through the workday lowered pistachio calorie intake by 22 percent compared with clearing them away every two hours. Study author James Painter, Ph.D., R.D., of Eastern Illinois University, explains that the work of shelling slows eating down while the pile of shells serves as a visible record of how much has been eaten. The findings are useful because they describe a portion control method that involves no calorie counting or food restriction, which may be of practical help to seniors, people with disabilities and anyone with reduced mobility who finds weight management harder when physical activity is limited.

At a Glance

• 1 - Pistachios supply about 160 calories per 30 gram serving, which is roughly 1 ounce.
• 2 - A 30 gram serving holds about 49 pistachio kernels, compared with 23 almonds or 18 cashews.
• 3 - Students who chose shelled pistachios ate an average of 211 calories, while those who chose in-shell nuts ate 125.
• 4 - USDA Agricultural Research Service findings suggest the fat in pistachios may not be fully absorbed by the body. That would mean pistachios deliver fewer calories per serving than once thought.

Topic Definition

Pistachio Principle

The Pistachio Principle is a behavioral eating concept which holds that people eat less when a food takes effort to get at and leaves visible evidence of how much has been consumed. The term was coined by behavioral eating researcher James Painter and takes its name from in-shell pistachios, where cracking each nut slows the pace of snacking and the growing pile of empty shells acts as a running tally. It is a form of mindful eating that works through the environment and not through willpower, lowering calorie intake without counting, restricting or changing what a person chooses to eat.

Overview

Two studies published in 2011 in the journal Appetite indicate that consuming in-shell pistachios is a weight-wise approach to healthy snacking, offering unique mindful eating benefits to help curb consumption and decrease calorie intake.

• The first study found that participants who consumed in-shell pistachios ate 41-percent fewer calories compared to those who consumed shelled pistachios.
• The second study revealed that pistachio nut shells can provide important "visual cues" as a reminder of consumption that translate into reduced calorie consumption.

Both studies further underscore that in-shell pistachios, which are one of the lowest calorie nuts, are a practical, everyday snack for weight management.

"In-shell pistachios are the original 'slow food.' The findings of these studies demonstrate that pistachios, as one of the only in-shell snack nuts, help slow consumption; and further, that the empty shells offer a visual cue, reducing calorie intake," said behavioral eating expert and study author, James Painter, Ph.D., R.D., Chair of the School of Family and Consumer Sciences at Eastern Illinois University. "In fact, the term 'Pistachio Principle' has been coined to describe a simple technique that can be used to help fool yourself full."

In-Shell Pistachio Consumption Curbs Calories by 41% Compared to Shelled Pistachios

The first study published in Appetite involved 140 university students assigned to consume either in-shell pistachios or shelled pistachios during class time. Both groups of students were provided a 16-ounce cup and asked to self-select a portion of pistachios to consume during class. Each student's cup of pistachios was weighed before consumption began. As students left the classroom, the remaining pistachios were weighed and recorded; total weight and calories from the consumed pistachios were also calculated. Those who chose shelled pistachios consumed an average of 211 calories while those who chose in-shell pistachios consumed an average of 125 calories, a 41-percent decrease in calorie intake.

The second study published examined the potential role of pistachio shells as visual cues of intake. Study subjects included 118 faculty and staff from a Midwestern university, all of whom were provided a pre-weighed 16-ounce bowl filled with four ounces of in-shell pistachios to keep on their desk over the course of two workdays separated by a day of no pistachio consumption. Participants were told they could consume pistachios at their leisure during the day and were also provided a second 16-ounce bowl to discard the empty pistachio shells.

The subjects were randomized using a crossover design to one of two groups. For the first group, the bowls with pistachio shells were not emptied until the end of the day. For the second group, the bowls with pistachio shells were emptied every two hours. Pistachios were added in two-ounce increments if the amount in the bowl had been reduced to approximately half or less of the starting amount.

"When leftover pistachio shells remained on the desk throughout the day, calorie consumption of pistachios decreased by 22-percent compared to when nut shells were routinely removed," said Painter. "Choosing in-shell pistachios instead of shelled nuts is a simple way to decrease calorie consumption without restriction. This is in keeping with existing research showing that when a person has visual cues of 'leftovers,' such as pistachio shells, they can see how many or how much they have eaten, helping to control portion size and consumption."

Pistachios - "The Skinny Nut" - Support Weight Management

This new data reinforcing the mindful eating benefits of in-shell pistachios adds to the existing body of research supporting pistachio's weight management benefits. According to researchers at the University of California Los Angeles, choosing to snack on pistachios rather than pretzels supports body mass index (BMI) goals. And research conducted by the Agricultural Research Service (ARS) of the United States Department of Agriculture (USDA) and  published in 2011 in the British Journal of Nutrition found that fat in pistachios may not be completely absorbed by the body, indicating that pistachios may actually contain fewer calories per serving than originally thought.

In addition to the data on pistachios, a study in 2011 by researchers at Harvard University found that consumption of nuts, as well as vegetables, whole grains, fruits and yogurt, was inversely associated with weight gain with nuts exhibiting a -0.57 pound effect on body weight.

Pistachios are one of the lowest calorie nuts with 160 calories per 30 gram serving (approximately 1 ounce). They also offer the most nuts per serving, providing about 49 kernels per 30 gram serving (approximately 1 ounce), when compared to other popular snack nuts - comparatively, almonds have 23 in a serving, walnuts 14 halves and cashews, 18. Pistachios are also a good source of fiber and protein.

References:

Two studies published in the October 2011 issue of the journal Appetite.

• Honselman CS, Painter JE, Kennedy-Hagan KJ, Halvorson A, Rhodes K, Brooks TL, Skwir K. In-shell Pistachio Nuts Reduce Caloric Intake Compared to Shelled Nuts. Appetite. 2011;57(2):414-417.
• Kennedy-Hagan K, Painter JE, Honselman C, Halvorson A, Rhodes K, Skwir K. The Effect of Pistachio Shells as a Visual Cue in Reducing Caloric Consumption. Appetite. 2011;57(2):418-420.

Li Z, Song R, Nguyen C, Zerlin A, Karp H, Naowamondhol K, Thames G, Gao K, Li L, Tseng CH, Henning SM, Heber D. Pistachio Nuts Reduce Triglycerides and Body Weight by Comparison to Refined Carbohydrate Snack in Obese Subjects on a 12-Week Weight Loss Program. Journal of the American College of Nutrition. 2010;29(3):198-203.

Frequently Asked Questions

Are pistachios a complete protein?

Pistachios contain all nine essential amino acids, and analysis of roasted pistachios has found they meet the standard to be classed as a complete protein for people aged 5 and older. A 1 ounce serving provides about 6 grams of protein.

Can people with diabetes eat pistachios?

Pistachios have a low glycemic index and combine fiber, protein and unsaturated fat, so they have little effect on blood sugar when eaten in normal portions. People managing diabetes should still count them toward daily calories and follow the advice of their own health care provider.

Are pistachios safe for someone with a tree nut allergy?

No. Pistachios are a tree nut and can cause serious allergic reactions, and people allergic to cashews are often allergic to pistachios as well because the two are closely related. Anyone with a tree nut allergy should avoid them unless an allergist has said otherwise.

How much sodium is in salted pistachios?

Sodium varies widely by brand, with roasted salted pistachios commonly containing more than 100 milligrams per ounce and unsalted varieties containing almost none. People on a sodium restricted diet for blood pressure, heart or kidney conditions should check the label and choose unsalted or lightly salted nuts.

What if arthritis or limited hand strength makes shelling pistachios difficult?

Buy shelled pistachios and measure one serving into a small dish before eating, then put the package away. This keeps the portion control benefit without the hand strain, and partly split shells can also be opened by using half of an empty shell as a lever.

How should pistachios be stored to keep them fresh?

Keep pistachios in an airtight container in a cool, dry place away from light. Because of their fat content they can turn rancid at room temperature over time, so refrigerate them for storage of several months or freeze them for up to about a year.

What vitamins and minerals are in pistachios?

Pistachios are a good source of vitamin B6, thiamin, copper, phosphorus and manganese, and they also supply potassium. They contain lutein and zeaxanthin, two antioxidants linked with eye health.

Can eating too many pistachios cause digestive problems?

Yes, large amounts can cause bloating, gas or loose stools in some people. Pistachios are high in fermentable carbohydrates called fructans, which can trigger symptoms in people with irritable bowel syndrome, and their fiber content adds to the effect.

Insights, Analysis, and Developments

Editorial Note: What stands out in this work is how little it asks of the person eating. Nobody was told to eat less - the shell simply got in the way, and the leftovers did the reminding. Painter calls this the Pistachio Principle, and the idea reaches well beyond one type of nut: any food that takes a little effort and leaves evidence behind is harder to overeat without noticing. It is worth remembering that both studies were short, one lasting a single class period and the other two workdays, and both took place on university campuses, so they show what happens in a sitting, not what happens to body weight over months. Related research cited here points the same direction, with UCLA researchers linking pistachio snacking to better BMI outcomes than pretzels and a Harvard analysis tying nut consumption to slightly less long-term weight gain. One practical caution is that cracking shells can be difficult or painful for people with arthritis, tremor or limited hand strength, and for them the same effect can be had by measuring out a single serving of shelled nuts into a small dish and putting the bag away.

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability, a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.