2011-11-30 Peter Pribis, MD, DrPH Cognitive Performance and Walnut Consumption in Young Adults
Cognitive Performance and Walnut Consumption in Young Adults
An Interview With Peter Pribis, MD DrPH
November 30, 2011, By Kirkham R. Hamilton, PA-C
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KIRK HAMILTON: Hi, my name is Kirk Hamilton, your host of Staying Healthy Today. And our message is simple: To provide you credible usable health information from interviews and our educational resources to help you Stay and Be Well in the busy modern world. Please take a few moments before or after listening to this interview to browse through the Prescription2000.com website, the home of Staying Healthy Today Radio, for our free educational services.Today's show topic is "Cognitive Performance and Walnut Consumption in Young Adults." Our guest today is Dr. Peter Pribis, a native of Slovakia who graduated in 1996 from Loma Linda University School of Public Health with a doctorate in public health. Since 2004 he has worked as Associate Professor of Nutrition and Wellness at Andrews University. He is a coauthor of the article entitled "Effects of Walnut Consumption on Cognitive Performance in Young Adults" in the British Journal of Nutrition, 2011.
Welcome, Dr. Pribis. Thank you so much for coming on the show today.
DR. PETER PRIBIS: My pleasure.
KIRK HAMILTON: So you have a very interesting background. You want to share a little bit of how you came to the United States and then how you got into nutrition and wellness?
DR. PETER PRIBIS: Well I was born in Slovakia which is a small country in Eastern Europe or Central Europe. I graduated in1988 from medical school in Prague. And then I came to United States and in 1996 I graduated also from Loma Linda University in California from School of Public Health with a doctorate in public health and my doctorate was in nutrition and epidemiology. After I finished my studies I actually went back to Europe. I spent three years in Czech Republic, four years in Germany, and in 2000 we moved back to United States. And presently I am the Associate Professor of Nutrition and Wellness at Andrews University, which is a small private Seventh Day Adventist university in Berrien Springs which is in Southwestern Michigan.
KIRK HAMILTON: Tell me why did you choose to specifically to come all the way to Loma Linda and then to focus on nutrition and wellness?
DR. PETER PRIBIS: Well I mean I was - being a Seventh Day Adventist, nutrition was something which always interested me. And in Czech Republic, or in Czechoslovakia at the time, you know, basically to study nutrition was actually totally impossible. So after the fall of communism I was lucky to get a scholarship and since I spoke English well I used the opportunity and so I ended up basically being at Loma Linda and getting my doctorate.
KIRK HAMILTON: Can you just basically share the tenets of the Seventh Day Adventists and how they view nutrition and diet?
DR. PETER PRIBIS: Well for the Seventh Day Adventist nutrition is part of their lifestyle and so they actually recommend - they don't require but they recommend to their members that they should be vegetarians. They are opposed, against smoking, drinking of alcohol and generally against drugs. And they basically view you taking care of your body as part of basically serving God.
KIRK HAMILTON: Do you know how many people really practice the vegetarian lifestyle as Seventh Day Adventists or you know they try a little bit, so to speak?
DR. PETER PRIBIS: Well yeah, I mean Adventists - actually Adventists became famous through what is called the Adventist Health Study. There was one done in the 70s there was actually a second one now presently going on. And if you look at the Adventist population, you would see that about - you know of course males, females differ, but let's say about one-third of them are vegetarians, I would say around one-third are semi-vegetarians, and one-third would be non-vegetarians. But you have to understand that even the non-vegetarians actually are not very heavy meat eaters. And on top of it Adventists do follow some regulations regarding meat. Which was actually based on the instruction, literature in the third book of Genesis. So they talk about clean and unclean meat, maybe you have heard about it. So therefore Adventists for example do not eat pork. They do not eat shrimp and crabs. So basically the only meat which they eat is beef or chicken.
KIRK HAMILTON: Okay.
DR. PETER PRIBIS: I'm sorry, lamb.
KIRK HAMILTON: That's all right. Let's - you wrote an interesting article which caught my eye.
DR. PETER PRIBIS: Right.
KIRK HAMILTON: And that's what I wrote you about. It's called "Effects of Walnut Consumption on Cognitive Performance in Young Adults."
DR. PETER PRIBIS: Right.
KIRK HAMILTON: So first of all, why did you choose to study that topic, walnuts and cognition?
DR. PETER PRIBIS: Well, I was always fascinated with nuts because you know they're food like, I don't know, grains and fruits and vegetables. But then there are certain foods which are very, very nutrient dense. And nuts belong into this category which means that it is really enough to eat just very little of them and you actually can experience quite a powerful impact of this consumption. So you - I was basically, you know I mean some people use it - they would probably call nuts power foods. So this was the one thing why I was always very fascinated with nuts. But the second thing was that if you look into the literature you will discover that there are truly hundreds of studies maybe which are done with omega-3 fatty acids but they all use fish oil. And so our study was very unique because as a source of omega-3 we did not use fish oil, but we used basically something which was plant based in our case it was walnuts. And as we all know the fish stock, as a source of omega-3, is under danger, but plant-based sources of omega-3 like walnut or flax seed, theirs is plentiful. All we need to do is to basically plant more orchards.
KIRK HAMILTON: Well let me hold you there for a little bit because I will be a little devil's advocate. I happen to be a vegan myself, but the alpha linoleic acid is the omega-3 fat that is rich in walnuts.
DR. PETER PRIBIS: Right.
KIRK HAMILTON: But you know in a biochemistry book it gets converted to EPA and DHA, which is in fish oil, but it doesn't work that well in humans, at least that's been my recollection from the data. So just because you take walnuts does not mean you're gonna get elongated EPA and DHA which is in fish oil which has been studied.
DR. PETER PRIBIS: Well you are right. If you are eating fish oil you are basically consuming directly EPA and DHA. When you are consuming alpha linolenic acid there are enzyme and this enzyme converts ALA into EPA and also in DHA, hence the effectiveness of the enzyme is rather low. Now the conversion rates for females for EPA are about 21% and for males about 8% and for the DHA it's about 9% for females and 4% for males. So the conversion is going on. It's just not very strong.
KIRK HAMILTON: So would you say then - I'm gonna again come from a devil's advocate point of view, and actually trying to educate myself a little bit, in that most people agree that we have too much omega-6 fats that are - lead to pro-inflammation and that's kind of a general theme. And so because we eat so much of those kinds of fats then everybody says pile on the fish oil to balance them out. And if the theory is we eat lower total fat diet and more plant-based omega-3s, would we balance that out a little bit better?
DR. PETER PRIBIS: Yes, but what is also true actually is that if you look into the literature you will discover that not everybody actually is today so excited any more about these you know ratios of omega-3 to omega-6. What they probably say, is that probably more important is the total amount of what you are eating. And like for example, even if you start to eat walnuts, walnuts contain a lot of omega-6 and but also omega-3. Omega-6 is generally more available or more present in fat, so every time you eat anything which is fatty, including walnuts or flax seed, you are increasing your omega-6 and also your omega-3. But the point is well taken that walnuts, and for example also flax seed, but in our case walnuts they do contain unusually high amounts of omega-3s. So when you are eating those, you know, you are truly skewing it in a sense and you are eating much more of omega-3.
KIRK HAMILTON: Alright. So let's get to the cognitive point. Is the goal of the walnut (consumption) to make more EPA and DHA and then have cognitive benefit, or is there something in alpha linolenic acid that does that?
DR. PETER PRIBIS: Well, before I answer it, let me just take one step back. The study which I have done was done with walnuts, which is a whole food, not a nutrient. And I think that this has the advantages, but also does have limitations. Now the huge advantage is, and I sincerely believe that we need more food studies. Is that when people go to a supermarket they do not shop for nutrients. They buy food. So for example, with my study the message is clear. Eat walnuts and the walnuts will cause this and this. However, the disadvantage is that if you look at for example walnuts, okay, walnuts contain all kinds of neural protective compounds. So they also contain vitamin E, they contain folic acid, they contain melatonin. There is actually several polyphenols which are very strong antioxidants, and of course they contain huge amounts of alpha linolenic acid. And because I have done it on food I am not able to literally pinpoint which nutrient was it. However, again, this is the beauty of food, is that when you eat food, there is a synergy and probably the synergy is sometimes much more powerful than when you just give somebody, you rip out a nutrient and you give it to people.
KIRK HAMILTON: You know I'm so glad - I actually set myself for that answer that you gave me. And what I mean by that is, I was you know, when I saw the article I got focused on omega-3 fats first and you just kind of knocked me upside the head and really in a good way. No, I mean I appreciate it and you said it so eloquently and perfectly that we should be looking at food studies.
So let's - tell me about your study and what you did and what you found out.
DR. PETER PRIBIS: Right. Well so what we did is, the idea was that we have discovered that, actually nobody studied up til now the effect of short-term intensive supplementation of diet with walnuts and cognition and so what we did is we actually decided to do it. And actually test it or we decided to test the cognition using four different tests. So the first thing what we did is we tested memory and the test for the memory was a very, very comprehensive test. It's called Wechsler Memory Scale. It's actually something which is done one-on-one and it takes about 90 minutes. So it's a very, very comprehensive test. The second test which we did is called Raven's. And actually this is a test which is the test of fluid intelligence. Now fluid intelligence is another word for actually intuition. So this is a test for which you don't even need how to read. It's just basically patterns and you need to be able to follow or to complete a pattern. Then the third test which we did is crystallized intelligence. In our case, this was actually critical thinking. And then the last test which we did is we actually tested the mood of the participants. Okay, now let me go systematically over the results. The first thing what we - well let me go over what was non- significant to what was significant. So we have unfortunately not discovered any effect of walnuts on memory. So there was truly no effect. However, I have to admit that maybe the reason why we have not actually discovered anything is because in epidemiology or in the research we call this "ceiling effect." The population which we used was 18 to 25. These were all college students. They're all bright. They're basically peaking in their memory development and so basically even adding walnuts to their diet simply did not help to improve their actual memory capabilities. Now the second thing, what we tested was the Raven's or the fluid intelligence or the intuition. And again this is nonverbal test which basically, you have to follow certain patterns and complete them, and again we were able not actually to find any effect. Now the next one which we tested was the crystallized intelligence and now the crystallized intelligence is very unstable. This is something which changes with level of education, with age, with other factors. And what we did, we tested actually using Watson-Glaser critical thinking test. Now what we were able to actually find is that there was a significant increase in inference.
KIRK HAMILTON: So that particular test, how would that be in real life? Give me an example of that.
DR. PETER PRIBIS: Yes. So basically, to simply put it absolutely simply inference, the capability of recognizing true from false. Okay. Now this is what it means. And so what we have discovered is that there was a mild improvement, about 11% and it was highly statistically significant. So if you want to really have a real life application to real life probably you know maybe students or young professionals because this is the age group on which our study was done. People who are in, I don't know math or physics, or you know any other science, in which they have to think critically and they have to constantly make decisions whether something is true or false. We probably think that those people when they eat walnuts regularly they might actually experience, or gain a slight advantage over people who do not eat walnuts.
KIRK HAMILTON: So how many, just curious, how many walnuts were consumed per day?
DR. PETER PRIBIS: Okay, so the participants, actually they did not eat walnuts because this was double-blind. What they ate, they ate banana bread. And then we ground it, the walnuts into it. So we had like banana bread with walnuts and without walnuts and those two were literally - they looked and tasted and smelled identical. And so those people who ate the banana bread with walnuts they consumed every day two cups.
KIRK HAMILTON: Wow, two cups of walnuts! That's a lot!
DR. PETER PRIBIS: Yeah. That's true. The daily intake or the recommended daily intake is one cup which would be about 30 grams. The reason why we went for, you know two cups for the maximum is, there are some studies showing that two cups is the maximum amount before you start to sort of gain weight.
KIRK HAMILTON: Well that was my next question. Was there a weight gain in this group?
DR. PETER PRIBIS: Yes, there was actually weight gain in both groups. Now -
KIRK HAMILTON: That's from the banana bread.
DR. PETER PRIBIS: Right. And now this study was basically done in two eight-week periods okay. So it was a double-blind cross-over so the same people eat once banana bread with walnuts and then once banana bread without walnuts. Now during the first eight weeks actually the people on walnuts, they gained about 2.6 pounds and the people on just banana bread gained about 1 pound.
KIRK HAMILTON: That's a difference.
DR. PETER PRIBIS: And this was actually statistically significant. Now during the second period after eight - then there was a eight week of washout and then again eight weeks. The people who actually ate walnuts, they gained half a pound and those who did not eat walnuts also gained about 0.4 pounds. Sorry - I'm sorry, this is kilograms, so 1 and 1 pound, and this was not statistically significant. So yes, there was a little bit of increase, but what we have discovered, we measured it, that was actually quite a bit of food displacement so once they started to eat the banana bread, we discovered that you know basically they ate less bread and pasta and you know and they actually drink more milk, I guess with the banana bread.
KIRK HAMILTON: There's a lot of compounding things.
DR. PETER PRIBIS: Yeah, so there was definitely a significant food displacement and they ate less of other things and then they simply ate the banana bread.
KIRK HAMILTON: So aside from the small weight gain as a side effect, was there any other side effects. Allergies or anything like that?
DR. PETER PRIBIS: No. But you know on the other side we asked - or we screened people before they even came into the study, so if somebody indicated that he is allergic we would not even accept him.
KIRK HAMILTON: Well, I don't know. I think in my life I have to make quick yes or no answers sometimes, so inferential reasoning would be good for me. I mean, we're always challenged with time and such.
Well, is there anything you want to wrap up here before we go that you'd like to say about your study?
DR. PETER PRIBIS: The thing is that our study was a short-term study, okay? So I cannot make any statements whether if somebody would eat for example walnuts continually whether he will for example experience continually this better inference. What we have simply done is we have done this for eight weeks and we have discovered after eight weeks already there was improvement. Now, just to wrap it up, we all know that - let's assume that the omega-3 in the walnuts were one of the really - one of the nutrients which contributed significantly to this, okay? We do know that whatever type of fat you eat, actually this type of fat will go into your membranes. And so we do assume that because those people ate so much omega-3 that this got into their brain membrane. And maybe because of this they became more plastic and more unstable you know. And there was maybe more production of certain neurotransmitters. And so we could assume that probably you know this is what caused all the things which we have been observing. Although as I said already, this was done on food so I cannot pinpoint nutrients. But I do think that the omega-3 had a lion's share in this.
KIRK HAMILTON: Well you know, I just - I thank you for doing the study and I thank you for re-reminding me of the importance of the whole concept of studying foods and how they affect different health conditions, and you can think of the vitamin E, the omega-3 fats. You said melatonin, correct, in the walnuts?
DR. PETER PRIBIS: Right.
KIRK HAMILTON: And polyphenols and fiber.
DR. PETER PRIBIS: Right.
KIRK HAMILTON: Okay. Well, Dr. Pribis, thank you so much for being on the show today, and I look forward to talking to you sometime soon.
DR. PETER PRIBIS: Yes. You're welcome, and have a nice time in Sacramento.
KIRK HAMILTON: It's wonderful. It's good weather here. Thank you so much for taking time out. Talk to you soon.
DR. PETER PRIBIS: Bye. Yeah, you're welcome. Bye.
KIRK HAMILTON: And I want to thank you, the audience, for listening to this edition of Staying Healthy Today Radio. And until next time, Stay and Be Well.
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