February, 2015

Research Perspective and Comments & Analysis

Pistachios Help Prediabetics Manage Blood Glucose Levels

By Mary Jo Feeney, MS, RDN, FADA, FAND, Nutrition Consultant, American Pistachio Growers

Nutrition research continues to highlight the health-enhancing properties of pistachios including specific benefits on glucose control.

Healthy lifestyles, including diet, are associated with lower risk of chronic diseases. A large body of evidence from epidemiological studies and controlled clinical trials points to the beneficial impact of nut consumption on health outcomes and total mortality.

Such benefits often are attributed to the nutrient composition of nuts — plant protein, fatty acid profile, presence of phytosterols, dietary fiber, vitamins, minerals, and bioactive compounds that function as antioxidants.

Relevance Of The Pistachio Research

Of particular relevance are the results of a randomized controlled clinical trial in which participants with prediabetes were able to achieve a healthier metabolic state by lowering risk factors such as fasting glucose and insulin.1 Prediabetes is the condition in which blood glucose/sugar levels are higher than normal but not high enough to be classified as Type 2 diabetes.

Without intervention, prediabetes is likely to progress into Type 2 diabetes in 10 years or less — this has far reaching implications for morbidity and mortality especially related to cardiovascular diseases.

Diabetes places a health care and financial burden on Americans. More than 29 million Americans have diabetes, and another 86 million — more than one in three adults — have prediabetes. Diabetes costs the country $245 billion annually, according to the American Diabetes Association.2

Pistachio research was undertaken to examine whether a pistachio-rich diet could reduce the prediabetes stage and improve its associated metabolic risk factors. Although pistachios were studied in relation to their high polyunsaturated fatty acid profile and cardiovascular disease risk factors, this study specifically examined pistachios’ effect on glucose metabolism, insulin resistance and risk of Type 2 diabetes when regularly consumed.

About The Pistachio Clinical Trial

The study involved 54 prediabetic adults (29 males and 25 females) with fasting glucose levels between 100 and 125 mg/dL who were randomly assigned to follow either a pistachio-supplemented diet (PD) or control diet (CD) in a crossover manner. A 15-day run-in period preceded the four-month intervention and a two-week washout period separated the two crossover interventions.

The control diet (CD) and the pistachio-supplemented diets (PD) were matched for calories, protein, dietary fiber, and saturated fatty acids. In the CD, 55 percent of the calories came from carbohydrates and 30 percent from fat. In the PD, 50 percent of the consumed calories came from carbohydrates and 35 percent from fat. The PD included 2 ounces (57g) each day of pistachios, half roasted, half roasted and salted. In the CD, energy intake from other fatty foods, mostly olive oil, was adjusted to compensate for the energy from pistachios included in the PD.

Weight, waist circumference, plasma fasting glucose and serum lipid profile, dietary intake, physical activity assessment, and markers related to inflammation and satiety was conducted at different time points during the study. Fasting glucose, insulin and HOMA (homeostatic model assessment) of insulin resistance decreased significantly as a result of the PD intervention compared to the CD. Other cardiovascular risk factors (oxidized LDL, fibrinogen and platelet factor 4) also decreased significantly under the PD compared to the CD.

The authors concluded results provide evidence that regular consumption of pistachios decreases glucose and insulin levels thereby improving insulin resistance and other inflammatory and metabolic risk factors. Thus, the inclusion of pistachios in a nutritious and balanced diet continues to emerge as a practical nutritional strategy to lower the risks associated with prediabetes.

More About Pistachios

Additional research on the role of pistachios in heart health, weight management, satiety, and as a post-exercise aid can be found at AmericanPistachios.org/research-archive.

1. Hernandez-Alonso P, Salas-Salvado J, Baldrich-Mora M, Juaola-Falgarona M and Bullo M. Beneficial effect of pistachio consumption on glucose metabolism, insulin resistance, inflammation, and related metabolic risk markers: a randomized clinical trial. Diabetes Care 2014; 37:1-8.

2. National Institutes of Health, press release: “National Diabetes Education Program Releases Guiding Principles for Diabetes Care.”


Five More Steps Needed To Make Real Progress

The produce industry, with its Fruits & Veggies – More Matters campaign and the, now superseded, 5 A Day program, has relied heavily on a general message of a pathway to healthiness by boosting produce consumption. This is an effort that has not succeeded.

There is, however, the hope that if we could identify more specific health benefits to be derived by consuming specific items, higher consumption might be achieved. It is not 100 percent clear if that theory is true. Research identifying benefits in the consumption of pomegranates and pomegranate juice — when backed by skilled marketers — certainly moved the needle on pomegranate-related consumption. It is not clear that this led to overall increases in produce consumption.

This is hopeful research, and if eating pistachios can help prevent the progression of prediabetes to full-blown diabetes, this would bode well as a major advance in public health.

Alas, as is always the case, this type of research is — to paraphrase Churchill — not the end; it is not even the beginning of the end; it is not even the end of the beginning. Before we can really begin to attribute such powers to pistachios or to any other food, at least five steps must be completed:

1) The research has to be repeated multiple times, by different researchers, at different institutions and with larger groups. This study included only 54 prediabetic adults — 29 men and 25 women. That is a start — but just a start.

2) The research has to be extended to actually note disease outcomes. They did not study people long enough to determine if, in fact, people who sustain the diet enhanced with pistachios actually are less likely to develop full-on diabetes.

3) Research needs to be conducted with various alternative diets. In this case, they had two choices: The control diet or the diet in which pistachios were added and other things reduced. As author Mary Jo Feeney explains: “In the CD, 55 percent of the calories came from carbohydrates and 30 percent from fat. In the PD, 50 percent of the consumed calories came from carbohydrates and 35 percent from fat.”

Even if the pistachio diet is better, this research doesn’t establish that it is pistachios, uniquely, that make it better. Perhaps it is the shift from carbohydrates that makes it better. After all, avoiding carbohydrates is a standard recommendation given to pre-diabetics. Maybe almonds would have the same effect?

A study based on a series of different diets of similar composition would be necessary before we can attribute unique health-inducing properties to a particular food.

4) Real world applicability also needs to be tested. This analyst confesses both to loving pistachios and to never once eating only 2 ounces of them at a sitting. Do typical prediabetic consumers, not operating under short-term research constraints, actually constrain their pistachio consumption to 2 ounces? If not, what is the dietary impact of consuming the typical amount consumed? Are the beneficial effects of the product outweighed by increased obesity due to increased calorie consumption? Or is the pistachio such a source of healthfulness that the more one consumes, the better off we are. Or are pistachios so inducing of satiety that people self-correct and consume fewer calories of other sources when they consume more pistachios?

5) Finally, of course, we need to study more people at different stages of healthfulness. For example, does this approach actually help people who have diabetes? Does it help people to not progress to a prediabetes state?

Of course, none of this is indicative of any flaw in the research. It is just an acknowledgement that as Laotzi, the founder of Taoism, taught us: “A journey of a thousand miles begins with a single step.”

And for the produce industry, it is a reminder of how high the barrier is if we wish to use science to persuade consumers of particular benefits of particular produce items. It means sustained investment in research. This particular study was done in Spain and partially supported by the American Pistachio Growers. They deserve commendation for undertaking the effort.

Because the industry has limited resources, we need to advance research to the point where the National Institutes of Health and major health insurance companies see enough potential to invest in larger studies at Johns Hopkins and Harvard.

Even then, even if we can show convincingly that pistachios or other items have important health benefits, the challenge will still be to find a path to not merely create a one-item boom — as with kale — but to choose information to change diet patterns in such a way that overall consumption of produce begins to rise.