MS. DIANE REHMThanks for joining us. I'm Diane Rehm. In recent years, doctors had begun to doubt that diets high in saturated fat and cholesterol cause heart disease. Now new research points to a compound found in red meat and supplements as the true culprit. Known as carnitine, it's converted by bacteria in our stomachs to a toxin that increases the risk of heart disease in both animals and humans.

MS. DIANE REHMJoining me to talk about the latest research on red meat and heart disease: Dr. Michael Lauer of the National Institutes of Health, Duffy MacKay of the Council for Responsible Nutrition, and, joining us by phone, Dr. Stanley Hazen of the Cleveland Clinic. I do invite your questions and comments. Join us, 800-433-8850. Send us your email to drshow@wamu.org. Follow us on Facebook or send us a tweet. Good morning to all of you.

DR. MICHAEL LAUERGood morning.

DR. DUFFY MACKAYGood morning.

DR. STANLEY HAZEN...for this very brief afternoon, and then I get on the plane, and I...

REHMDr. Hazen, are you there?

HAZENMeaning...

REHMDr. Hazen, are you there with us?

HAZENThis is the A-S-T-I-A...

REHMOK. Dr. Hazen, are you there with us? I'm sorry. I guess we all have to get Dr. Hazen back on the air. I'd appreciate, Dr. Lauer, your reaction to this study that was done at the Cleveland Clinic. First, tell us about it.

LAUERSure. Well, a couple of years ago, Dr. Hazen published a paper in which he showed that gut bacteria played a role in promoting vascular disease. What he showed was that a common dietary substance called lecithin is broken down by bacteria that live in our colon, and that in turn then leads to the formation of a substance called TMAO, which seems to promote the development of hardening of the arteries. What he did in this study was he looked at another substance called carnitine.

LAUERCarnitine is found in red meat. And he found that carnitine seems to act in the same way. It is acted upon by bacteria in the gut, which then leads to the formation of the same substance, TMAO, that promotes the development of atherosclerosis. And what this suggests is that the bacteria in the gut may play a major role in the development of this most common chronic disease.

REHMAll right. Dr. Hazen, are you there now?

HAZENI'm sure there will be...

REHMDr. Hazen.

HAZEN(unintelligible)...

REHMAll right. Dr. Hazen, are you there now?

HAZENI think he's...

REHMGoodness gracious, we are having a problem here. What do you think, Dr. Lauer, prompted this study?

LAUERWell, we've known that vascular disease is due to a variety of causes. It's what we call a complex multifactorial disease: diabetes, high blood pressure, high cholesterol. But we still have not -- although we've made a lot of progress, we still haven't figured out a way to make it entirely go away which suggests that there are some other pathways involved as well.

LAUERSo what Dr. Hazen did was he looked at a very large number of patients that he was taking care of, and he was using modern technologies to try to identify various metabolites, chemicals that are in the blood that are in higher levels in people who have disease and in people who don't. And this is how he found these particular metabolites that seem to be produced by gut bacteria.

LAUERNow, why this is important is that it suggests a whole new paradigm, a whole new pathway of thinking about what gut bacteria do and what may be potential causes of this disease. And then this opens up a whole vista of potential research which could -- might lead to new ways of preventing or treating hardening of the arteries.

REHMTell me about carnitine. Never heard of it, and yet I gather it is in some supplements, some power drinks. What does it do?

LAUERWell, carnitine is actually a vital substance. We need it in order to live. Carnitine plays a role in transporting fat from the outer part of the cell into the part of the cell that's responsible for energy. And, in fact, there is a disease which is called carnitine deficiency. There's the genetic form of it. And people who have this disease are very sick.

LAUERTheir muscles don't work. Their hearts don't work. They can develop some very serious problems. We get carnitine -- most of our carnitine comes from the diet. It comes in red meat and dairy products. But we can also get carnitine by our own body. Our own body's capable of making it.

REHMAll right then. Dr. Hazen, are you there with us now?

HAZENYes, I am. Thank you.

REHMI'm so glad. Tell me why people take carnitine as a supplement.

HAZENWell, it's thought to help increase energy, although the data on that is rather soft. Carnitine is essential for moving fatty acids from outside of the mitochondria to inside the mitochondria, the powerhouse of the cell. And -- but our bodies can make all of the carnitine that we need. It is not an essential nutrient in as much as you don't have to ingest in your diet carnitine since we synthesize all the carnitine we need if you're a normal, healthy individual.

REHMSo exactly what happens when red meat gets converted to this TMAO in our bodies?

HAZENWell, what we found is that carnitine ingestion leads to accelerated atherosclerosis or hardening of the arteries, and this was found both in an animal model, and then we also saw in humans that increased carnitine levels in the blood tracked with increased risks for heart attack, stroke and death.

REHMSo are you also saying that the same thing happens when a person swallows carnitine in pill form?

HAZENYes. What we saw is that, both in the animal model and in humans, when you ingest carnitine, microbes that live in our intestines digest the carnitine, and as a byproduct, they make something that gets converted into a compound called TMAO which, in previous studies and in the current studies, we showed, accelerates heart diseases.

HAZENNow, the mechanism of how it accelerates heart disease was that it actually changed cholesterol metabolism. So in the presence of TMAO, cholesterol metabolism in the artery wall, in the liver and in the intestines was influenced, and the net effect was increased depositing of cholesterol and cells of the artery wall and decreased removal of cholesterol from the peripheral cell like in the artery wall.

REHMAll right. So how preliminary a study do you think this is? Or are you telling people, right now, cut down or cut back on the amount of red meat you consume?

HAZENWell, the studies are both preliminary, but they also have quite a large number of people in it. This had over 2,500 individuals. We already are suggesting -- we have been suggesting to patients that they cut back on red meat ingestion or consumption because many studies have shown that increased ingestion of red meat in the diet is associated with increased likelihood of experiencing a heart attack, stroke or dying. It's associated with cardiovascular disease.

HAZENAnd that risk appeared to be disproportionately high compared to what the cholesterol level or the saturated fat level of red meat was. There was an excellent study by the Harvard School of Nutrition last year that looked at different communities or populations in their red meat consumption and focused on this and said that just one extra portion per day of red meat was associated with about a 13 percent increase in risk.

REHMSo now, what about you? Are you a vegan or a vegetarian?

HAZENNo. I used to be a carnivore, and now I'm a vegetarian/omnivore. So I've just cut back on the amount of red meat that I'm eating and...

REHMWhat does that mean, cut back?

HAZENWell, I used to eat it probably five times a week in one form or another, you know, as a sandwich, or, you know, if you really look at what you do in your diet, oftentimes, you find you're -- at least I found that I was having red meat and -- not just as a steak, but as, you know, as a piece of a dinner or a piece of a meal. Now I'm actually doing about two portions a week.

REHMAnd what about carnitine? Would you recommend against taking it as a supplement?

HAZENI think that unless there are some compelling circumstances, such as what Dr. Lauer was discussing, someone with carnitine deficiency, but that's a rare genetic disorder. Or it is also very rare to have a secondary carnitine deficiency that's seen, for example, in patients sometimes after chronic dialysis for long periods of time.

HAZENOutside of those circumstances, I would argue against taking supplemental carnitine, unless they're, you know, instructed so by your physician because just an apparently healthy subject taking carnitine off the shelf at the grocery store or at the local nutrition shop, most of the time, there's not really a clear indication that it's needed. Your body can make all the carnitine it needs even if you're a vegan and never eat any meat products.

REHMSo you're saying that vegetarians are less likely to have the problem even though they are not taking carnitine as a supplement or eating red meat?

HAZENThat's correct. What was -- one of the remarkable findings of the present study was that we saw that vegetarian or vegans metabolized carnitine substantially differently than what you saw in an omnivore.

REHMInteresting. All right. Dr. Stanley Hazen, chair of the department of cellular and molecular medicine at the Cleveland Clinic.

REHMAnd welcome back. You've just heard Dr. Stanley Hazen of the Cleveland Clinic. He was one of the lead authors in a new study talking about the effects of red meat and its conversion in the body to create a compound that apparently raises the risk of heart disease. And we had a little trouble there at the start with the phone. But, Dr. Michael Lauer, can you add anything to what Dr. Hazen had to say? He did have to leave us.

LAUERSure. I think one of the most important messages here is that this opens up a whole new potential way of thinking about the role of bacteria that live in our gut and what these bacteria may be doing for our health and putting us at risk for disease. We've traditionally thought of these bacteria as bystanders. And yet there are trillions of them that live in our body.

LAUERAbout 99 percent of the DNA in our body comes from bacteria. It doesn't actually come from our own human cells. And through the work that Dr. Hazen and other scientists are doing, we're coming to appreciate that we need to pay attention to this. This may play an important role in figuring our who's fat, who's not, who's healthy, who's not.

REHMAnd just to clarify, someone has written in an email, who says, "By supplements, do you mean antibiotics and growth hormones?" We're not talking about that now.

LAUERNo. No.

REHMIn fact, we're talking about a natural occurrence in the gut of human beings when they eat an excess of red meat.

LAUERYes. We're talking about how the bacteria in the gut react to diets that we eat.

REHMExactly.

LAUERAnd it turns out that what kind of diets we eat may have a dramatic impact on what kinds of bacteria live in our gut and what they're doing.

REHMAll right. Duffy MacKay, you are with the Council for Responsible Nutrition. How do you react to what you've heard from Dr. Hazen and Dr. Lauer?

MACKAYWhen studying diet and nutrition, it's really important that we learn from the past and realize that when we drill down into one component of a diet or even further into one molecule within that component of the diet, it can often be misleading. And we could have seven guests around this table today talking about what's in red meat, and one of them would tell us it's the cholesterol that's causing the problem. One of them would tell us it's the saturated fat. Another would tell us it's the omega-6 fatty acids.

MACKAYAnother might tell us it's because we cook the meat and the various carbon compounds that are created after we cook the meat. Each one would have equally compelling data, and each one would have a convincing story and a career to back it up. So I think it's really important that consumers realize, before we run out and change behaviors, that there are reasons that we supplement with L-carnitine. We've touched on some of them. And there are clinical studies that show us L-carnitine supplementation is safe.

MACKAYSo we're talking about a lot of different things. We're talking about the emergence of gut bacteria and the role of human health. We're talking about various biomarkers that might be found in different types of diet, whether it be omnivore or vegetarian. But what we're not talking about, what we need to keep talking about is what are the other differences between a vegetarian and an omnivore? A vegetarian gets more fiber. They get a different spectrum of nutrients. There's a lot of different things that could be responsible for what we're talking about.

REHMHow do you respond, Dr. Lauer?

LAUERWell, for the most part, I'm in agreement with what Dr. MacKay is saying. This is part of a very complex tapestry. This is not the be all and end all. It is one very interesting, potentially path-breaking study. But a lot more work needs to be done. And it does have to be put within the context of a much more complex environment within which we live and eat.

REHMHe did talk about the fact that this study has been involving 2,500 human beings as well as animals. And I gather consistency was the word.

LAUERYes. It is actually quite remarkable. The way this work was done is it started in the clinic. There were observations made in the clinic that then stimulated some work in the laboratory. The laboratory work then stimulated more work back in the clinic. So it's a beautiful example of how research can go from the clinic to the lab and then back to the clinic again. But now what needs to happen is this needs to be replicated in other animal models and other patients. And much more needs to be done.

REHMAnd it would seem, Duffy MacKay, that the results on both humans and mice pointed to carnitine as the cause of higher levels of the toxin TMAO.

MACKAYWell, we also know that other trimethylamines can be metabolized into TMAO, so this is one potential source of TMAO. And I would like to clarify that we do have data on 2,500 individuals, but this is just human biomarker data. This is just measuring various biomarkers that are found in omnivores versus vegetarians. We did not intervene in these subjects. There was a much smaller number of subjects where they actually did some supplementation and some measurements after. I think a total of six.

MACKAYSo it's important to place this data into context 'cause 2,500 sounds very convincing. But if you take 2,500 vegetarians and you start measuring biomarkers in those individuals, you're going to find a lot of differences. A lot of nutrient levels will be different. A lot of markers of fiber metabolism by gut microbes will be different. And any number of those could be pointing to as causative agents.

REHMDr. Lauer, would you change your diet on the basis of this study?

LAUEROn the basis of this study alone, no.

REHMAre you an omnivore?

LAUERI am a gluten-free, sugar-free vegan six days of the week, and one day of the week, I eat chicken. And very rarely I'll eat red meat.

REHMSo you would not need to change your diet.

LAUERThat's right. That's right.

REHMAnd what about you?

MACKAYFor me, diet is about moderation in context. And so for me, what's more important that I fill my plate with the right amount of vegetables, fruit, things that I know are positive and good for me. I love fish. I eat sardines all the time. But I do enjoy red meat. But I understand that all of the data, including data on other components in red meat, including how my own body feels, is telling me I need to eat it in moderation.

REHMDr. Lauer, what about carnitine supplements? Where are you on that?

LAUERWell, I'm completely in agreement with Dr. Hazen that unless there is a compelling medical reason, and there are...

REHMAnd there are some.

LAUERThere are some. And unless it's under the direction of a physician, I see no reason for it.

REHMOK. Dr. Hazen mentioned those who've been on dialysis. What other conditions might prompt the doctor to prescribe carnitine?

LAUERThere are some drugs. For example, there are drugs that are used for epilepsy. There are drugs that are used in transplant patients which can induce carnitine deficiencies. And under those circumstances, it may be appropriate. There's also a carnitine deficiency that can occur in the elderly, people who are very malnourished, who may develop muscle weakness on account of that.

LAUERAnd that may be another circumstance in which carnitine supplementation may make sense. There's also some literature on using carnitine in patients with neuropathy. This is where the nerves in the peripheral parts of the body aren't working quite right. So there are some specific circumstances where it may be appropriate. But for the most part, I don't see any reason for it.

REHMSo you would not recommend people taking it as a regular dietary supplement?

LAUERNo.

REHMAnd how about you?

MACKAYI would agree with both of the physicians so far that there are many reasons listed, as well as others, I mean, intermittent claudication, poor blood flow.

REHMWhat does that mean?

MACKAYOh, other conditions for which a clinician, especially a clinician that uses nutrition as one of its interventions, would use L-carnitine. And the important thing is there are studies.

REHMBut you haven't explained to me why.

MACKAYOh, to improve circulation, to...

REHMCirculation.

MACKAYCorrect. There is a handful of clinical studies in intermittent claudication, which is a condition of unknown cause which causes poor circulation in the extremities.

REHMHow about that, Dr. Lauer?

LAUERWell, I agree with Dr. MacKay that the literature is out there, but I don't think it's compelling.

REHMYou do not think it's compelling?

LAUERNo. No.

REHMSo in what Dr. MacKay just said, you would not agree?

LAUERYes.

REHMAll right.

MACKAYAnd -- but it's important to remember that science grows in increments, and each one of these areas where we're beginning to understand that L-carnitine supplementation may be beneficial, the door is open for additional research to either convince clinicians like Dr. Lauer or otherwise -- for example, other conditions of wasting situations, HIV wasting, anorexia. There are other conditions where we see muscle wasting, including the elderly, including inborn errors of metabolism, premature infants.

MACKAYL-carnitine is often added to infant formula for premature infants to help them deliver this important amino acid at a stage of life. So I think we're all in agreement that it's an important choice for people who use nutrition in medicine, as well as there is some data that suggest it can help athletes with exercise, recovery, some performance. Now, I agree that that data goes both ways. Some studies showing it has positive effects. Some showed study no effect.

MACKAYBut athletes are a unique bunch, and they're going to do what -- if it's safe, and clinical studies have been shown it's to be safe up to two grams up to six months, athletes may want to try that. They want that choice. If it's manufactured safely and they're taking L-carnitine, there's no reason they shouldn't have that option.

REHMDr. Kay, what -- MacKay, what is your relationship to L-carnitine?

MACKAYNot a cousin, not a friend. I don't really have a relationship. I just know that it's something that is -- it's in our diet, and I practice integrative medicine. I'm a naturopathic doctor. So we use nutrition as a tool in the medical setting. So I try to understand the physiology and how I can manipulate that...

REHMSo considering what you've heard from Dr. Hazen and Dr. Lauer, would you continue to offer carnitine to anybody and everybody?

MACKAYWell, no, that's not what I had said. I...

REHMWell, but if you're talking about athletes.

MACKAYWell, we -- I always advise that, no matter what you're taking, no matter what you're putting in your mouth, you talk with your physician about it. And you work out -- you know, you let them know what you're taking. And if you're an avid athlete -- and they understand that, and they're helping you stay healthy through that process -- they should be able to look at the data and say, look, let's give you a period of time. Take the L-carnitine. Let's see if it improves your performance. Let's look for any negative effects. But let's do it in a -- with both eyes wide open.

REHMWhat do you think, Dr. Lauer?

LAUERWell, I do think that people should not be making these kinds of decisions on their own without careful consultation with their physicians. I also think -- I agree with Dr. MacKay that science is an incremental discipline. And so we must be careful about over-interpreting any one individual study. And what we're looking for is a compelling body of evidence that develops over time before we convert that into practice or policy.

REHMAnd you're listening to "The Diane Rehm Show." And joining us now is Shalene McNeill. She is joining us from San Antonio, Texas. She is executive director of human nutrition research for the National Cattlemen's Beef Association. Good morning to you, Shalene. Thanks for joining us.

MS. SHALENE MCNEILLThank you for having me, Diane.

REHMTell me what your reaction was to the new study on red meat.

MCNEILLYou know, I agree with Dr. Lauer that this opens a whole new way of thinking about nutrition. It's definitely an interesting study. It's a well-done study about how, as we've talked about, this single nutrient can be metabolized in the gut. And without a question, it's going to spawn more research, and we're going to need more research. But I don't think there's anything in this study that supports the need to cut back on meat intake, and I think you asked a really important question about what does cutting back mean.

MCNEILLI mean, the fact is -- and this may be really surprising to hear, but average beef intake is less than two ounces per day. So Americans are eating beef well within dietary guidelines, and they're getting lots of other nutrients besides L-carnitine, so things like high-quality protein and zinc and iron, many essential nutrients. So it really is about the total diet, at the end of the day.

REHMWhat's your total reaction to carnitine?

MCNEILLI mean, I think that, prior to this study, there is a lot of evidence on the health benefits of L-carnitine. So I think we've been talking about the need to put this under the context of the total body of science. I think we also have to understand what happens when you eat L-carnitine in the matrix of a food and in the matrix of the total diet. And then your gut is different than my gut. So there are so many questions that we don't know.

MCNEILLYou know, I'm a registered dietician feeding two daughters and a husband, and I think, what are we going to do for dinner tonight? And so I don't think there's anything in this study that changes what we'll do for dinner tonight, but it's an important step in scientific discovery to understand not only how L-carnitine but other nutrients are metabolized by the gut.

REHMSurely. And what about the statement from Dr. Hazen that this study indicates that red meat consumption could lead to heart disease?

MCNEILLYou know, I think Dr. MacKay pointed out that you can look at variety of mechanisms. But one of the things that Dr. Hazen said that I think is really important, he pointed to some data from Harvard School of Nutrition. But there's -- there is another study from Harvard School of Nutrition with a million subjects that shows no association between red meat and heart disease.

MCNEILLSo we can point to individual studies that are very inconsistent. At the end of the day, what we have to look at is the total body of evidence, and I think that it's clear that the scientific evidence to support the role that beef plays in a healthy and balanced diet is strong. You know, certainly we've talked about some of our eating patterns.

MCNEILLI happen to be a frequent meat-eating, healthy dietary pattern person. So I love edamame and fish and clementine oranges, but I also love beef. And I find that it makes an important contribution not only to my diet, but to the diet of my growing girls and my husband. So I think that we've got to look at broadening our understanding of what constitutes a healthy dietary pattern.

REHMDr. Lauer, from your perspective, would you recommend if you were a physician talking with patients, on the basis of the work of the Cleveland Clinic, what would you say to patients?

LAUERWhat I would say to patients is there's no need to change the advice that I'm giving them on the basis of this study alone. But I would also tell them that if they're interested in this kind of thing, get involved in research. There's a lot of ongoing research in the world of diet. Find out what projects are going on in your area and become part of it, become part of the solution. Join the gang.

REHMSo you would not say to any patient, perhaps on the basis of what we've learned from the Cleveland Clinic, it might be wise to at least somewhat reduce your intake of red meat.

LAUEROn the basis of this study alone? No, I would not say that. As your caller correctly pointed out, the amount of red meat that we're eating is a lot less than it used to be, and that should stay.

REHMAll right. Short break. When we come back, we'll open the phones.

REHMAnd welcome back. We're talking about a new study that's just come out from the Cleveland Clinic showing that there may be a connection between red meat and how our stomachs process that red meat which could lead to the development of a bacteria that actually may produce heart disease. We're going to go first to Indianapolis. Good morning, Catherine.

CATHERINEGood morning. Thank you for taking my call.

REHMSurely.

CATHERINEI have a comment, a quick comment and a question. I think that the -- as one of your speakers just recently said, you know, my gut is different from your gut is different from his gut. And it seems to me that, instead of everybody getting, oh, my gosh, we have to avoid red meat, we should look at our own individual histories.

CATHERINEI have no family history of high blood pressure or heart disease, so I figure I'm probably a little more safe to eat red meat. I just wanted to throw that in there. But I do have a question, very early on, there was a mention that carnitine comes from red meat, but it also comes from dairy. If I was a person who was at high risk for heart disease and is wanting to try and limit my risk factors, in addition to avoiding red meat, should I also avoid dairy?

REHMDr. Lauer.

LAUERThe major concern with dairy has been saturated fat. Whole fat dairy products do have a fairly large amount of saturated fat. And so for that reason, dietary guidelines recommend low fat or skim dairy products. As far as this particular issue is concerned, I don't think there is any new actions that need to be taken.

REHMAll right. To Beaufort, N.C. Good morning, Sheryl.

SHERYLYes, thank you for taking my call.

REHMSure.

SHERYLI have a quick question for you guests, and that is, what is actually considered red meat? For instance, is pork considered red meat or not?

REHMCertainly. Dr. MacKay.

MACKAYWe just had that discussion in here. Other folks have had that question. And we determine the conclusion is that it's all mammals. It's going to be your beef and your pork and your lamb and other things, but not your fish and not your poultry.

REHMNot poultry. All right. And to Mike in Manassas, Va. Good morning.

MIKEGood morning. And, everyone, how are you?

REHMGood, thanks. Go right ahead, please.

MIKEMy question is this: Are there external factors to this like the injection of growth hormone and antibiotics and the effect on this process that we eat?

REHMWhat do you think, Dr. Lauer?

LAUERI heard the question was about antibiotics in growth hormones. So, yes, there are concerns about this. Antibiotics both in feed cattle as we as in people may affect the kind of bacteria that are in our environment and that live in our gut. And that may have effects on our risk for disease.

REHMAll right. Here's an email from Steve, who said, "Your guests said carnitine is metabolized differently in omnivores and vegetarians. What are the difference and their effects?" Dr. Lauer.

LAUERYeah. So what was particularly interesting about this study was that the investigators looked at what effects carnitine had in people who are vegans and vegetarians and those who aren't. People who are vegans don't produce this substance, this substance called TMAO, which seems to promote vascular disease. And it may be because the gut bacteria that would convert carnitine ultimately to TMAO are not there in people who don't eat meat.

REHMAnd here's a question from Mohamed, (sp?) "My son has developmental disorder, and one of the daily supplements prescribed for him is L-carnitine. I need to know if he is taking something that's not good for his cardiovascular system." Dr. MacKay.

MACKAYWell, I would encourage you to ask that question to the treating physician of your son. Presumably, there is a reason that he's being supplemented with the L-carnitine, and it is related to his condition. So one would assume that his body is using it properly for specific needs like preventing cachexia or wasting. In that situation, it would not be available for this metabolic process that we're referring to that would convert it to TMAO.

REHMDr. Lauer, would you agree?

LAUERYes.

REHMAll right. And to, let's see, Diego in Miami, Fla. Good morning. Diego, are you there?

DIEGOYes, I'm here. Good morning. How are you?

REHMFine, thanks. Go right ahead, please.

DIEGOYes. I just have a question in regards to adopting a plant-based whole foods diet and obviously, the effect on, you know, heart disease and all these other new things that we're looking pretty much every single day. I just wanted to ask your panel that question.

REHMYou mean a diet based on plants.

DIEGOYes.

REHMOK. Dr. Lauer.

LAUERThis has been a long-standing debate. There is evidence that people who live on primarily a plant-based diet may have lower risks for developing chronic disease. Ultimately, the way we answer this kind of question is by doing large-scale trials. And we saw an example of that actually a couple of weeks ago with a trial from Spain that suggested that a certain kind of diet called the Mediterranean diet supplemented with olive oil may lead to lower rates of developing heart disease and stroke.

REHMAll right. And here's a tweet from someone calling himself sumoburner, (sp?) "What about the carnitine in energy drinks?" Dr. MacKay.

MACKAYWell, we've heard today that the body makes significant pools of carnitine that are available to us. And therefore, the carnitine that's available to energy drinks is negligible as far as we call exogenous or external sources of carnitine. So I am not concerned. In addition, we do have evidence of carnitine supplementation for outside that shows it's safe.

MACKAYThen you have to overlay this concept of which gut bacteria do you have. So if you are a vegan taking an energy drink and you really bought into this research as definitive, you would say there is no concern because you wouldn't be converting it. If you are a carnivore consuming an energy drink, the presumption is you would be making some of this TMAO.

REHMAll right. To or here in D.C. Good morning, Paul.

PAULThanks, Diane. Great show, and thanks for having me on.

REHMSure.

PAULI have a family history of heart disease and cancer. And when I was young, as a child, I was very overweight. I was fat. And I decided to become a vegetarian and then a vegan at the age 13. And very quickly, I lost the fat. I gained the muscle. I had -- even as a child, I even had high cholesterol. That all came down, and I've been a vegan now for about 20 years and my cholesterol was down at around 100.

PAULI'm an avid athlete, and I'm convinced that this plant-based, whole food vegan diet is responsible for this. And one book that was very influential on me was "The China Study" by T. Collin Campbell which looks at the literature on plant-based diets and how they are associated with lower risk of heart disease, various cancers, Type 2 diabetes and more.

REHMCan you talk about that, Dr. Lauer?

LAUERSure. Well, first of all, good for you, and I'm glad to hear that you're doing so well. This, as I mentioned before, is a long-standing debate. And whether or not we should be recommending a plant-based diet, a sole plant-based diet for everybody, we're not there yet. We need a lot more evidence to suggest that. And I think what needs to happen is many, many more large-scale trials to figure out what kinds of diets or dietary supplements are best for us.

REHMShalene, what's your reaction?

MCNEILLYou know, I'm listening to the discussion, and I think there's a lot of misperceptions about what a plant-based diet is because, for example, right now, most of the calories in the American diet are already plant based. So I think what we're saying is that we want and we see value in increasing the fruits and the vegetables and the whole grains in our diet, but that doesn't have to be at the expense of meat.

MCNEILLI'm thinking about a study that was just published a couple of weeks ago that showed 40 percent of the calories in adolescent girl's diets are coming from junk food, empty calories, 40 percent. So when I look at that as a registered dietician, I'm thinking, what a huge opportunity for improvement to include more nutrient-rich food in those diets.

MCNEILLAnd in this particular study, looking at this adolescent girl, what they showed is that girls that were eating nutrient-rich dairy and nutrient-rich beef were more likely to get the vitamins and minerals and the nutrients that their bodies needed, and they were less likely to eat those empty calories. So I think in some cases, we can be really interested in this very important research around scientific discovery.

MCNEILLBut at the end of the day, we have to think about what's practical for people today, and it doesn't take a dramatic change in your diet to make some improvements. You know, just trying to consume more nutrient-rich foods can have a huge impact. And as we, you know, if we think about dietary guidelines and actually making it doable, the biggest challenge is that people aren't following any of the dietary guidelines.

MCNEILLSo we have to make it within reach, and that can be through changes like enjoying lean beef, enjoying nutrient-rich sides to go with that. So I don't think you have to make a major change in your diet to have a huge impact on your health.

REHMDr. MacKay.

MACKAYYes. I think we stumble across an important concept that, you know, once we start to villainize once component of food and attach a moral value to it, it's either good or bad, there's sometimes unintended consequences. And we know that when we told people that saturated fat was bad, what did we do? We start eating more carbohydrates. Many of those carbohydrates are plant based.

MACKAYSo we just need to be careful, and that's why I caution to that when over interpreting this kind of reductionistic or molecular science into patterns, we can be misled. And it's important -- as we've heard many times to place this is on the context and as much as something in the meat might not be good in excess, we might actually be looking at more -- what are we missing? Fiber, no one eats enough fiber. And so add the fiber in relation to the meat, plus the exercise, plus the healthy gut bacteria, and maybe we're looking at wellness.

REHMAll right. To Heather in Charlotte, N.C. Good morning.

HEATHERHey. Good morning, Diane. Thanks for taking my call.

REHMSure.

HEATHERSo this is a really interesting discussion. I actually supplement my diet with around 3,000 milligrams of L-carnitine a day based on some of the research that I've read online really as a weight loss sort of supplements in addition to CLA. And, I mean, I eat red meat probably around once a week in addition to, you know, plenty of fruits and vegetables.

HEATHERSo I'm just wondering based on the discussion from the panel today, is it really lending me the benefit of supplemental weight loss? Or is there a potential harm in what I'm doing from a lot of the discussion around, you know, the impacts to the heart?

REHMSure. Dr. Lauer.

LAUEROh, I think the only honest answer I could give you is I don't know. And given -- when I was in medical practice, I tended to be fairly conservative and say, well, if I don't really know whether or not this is the right thing to do, it's probably a good idea not to do it and focus on those things that we know work.

REHMHow about you, Dr. MacKay?

MACKAYI think you have to be -- put it in perspective of, are you achieving your weight loss goals? There are some evidence that it might give you some help, but it's not going to be a magic bullet. And so if you have the discipline to reduce total calorie intake and increase energy expenditure and you can create a sustainable long term, the L-carnitine is a great kick start to get you motivated. You should, you know, use it, but at the same time, your long-term goal for maintaining healthy weight should be based on diet and energy expenditure.

REHMAnd you're listening to "The Diane Rehm Show." But we go back to the study from the Cleveland Clinic. Would 3,000 milligrams seem to be a fairly hefty size of a dose for one person to take simply for weight reduction considering what the side effects, long term, could be, Dr. Lauer?

LAUERYes. And I cannot really justify it. I don't know whether it's going to be helpful. This particular study suggests it might be harmful. Since you are interested in this, you might want to find out what kind of research projects are going on in your area that are related to diet and supplements and join them.

REHMAll right. Let's go to Cincinnati, Ohio. Jean, you're on the air.

JEANGood morning, Diane.

REHMHi.

JEANGreat show as always.

REHMThank you.

JEANAs a physician who has cared for patients with cardiovascular disease for over 25 years, I think there's really no question as to the fact the greatest risk factors for cardiovascular disease are smoking, obesity and genetics. And so my question really is, are we not -- in looking at lecithin and these effects of red meat, are we not just rearranging the deck tiers on the Titanic by, you know, looking at this and whether or not to what's importance is really secondary to these other well-known overwhelming risk factors?

REHMDr. MacKay.

MACKAYI think this is a very good point to place in context on this type of research. I do think that this research could lead to a better understanding of gut microbes. And that's an area where we really do need to begin to expand the relationship between what lives inside of us. I mean, there's as many bugs in our stomach as there are cells in our body.

MACKAYAnd they convert vitamins and activate vitamins, and they have a major influence on how our food interacts with our bodies. So in that respects, I think we are sitting on top of the iceberg in the -- just at the tip of how we're going to begin to able to influence human health. I absolutely agree that when it comes to preventing cardiovascular disease, we have some large benchmarks that we can continue to chip away at, and we should not lose sight of those.

REHMShalene.

MCNEILLThank you for the opportunity 'cause I would just echo what the caller shared. And that is, you know, we really do -- we're living in fast-paced busy world, and we've got to make small changes to improve our health, and it can be really overwhelming. And we can hear studies like we're hearing today that are so complex and can be really confusing.

MCNEILLAnd I think what your physician caller pointed out is that let's start with the things that we absolutely know make a difference. We can all do small steps to manage our weight and get physically active and not smoke and other healthy behaviors that we can start to change. So I think we need to stay focus on that and find ways that we could do it. And it's going to be different for everyone. How we achieve a healthy dietary pattern is going to be different, and that's OK.

REHMAll right. And, finally, Dr. Lauer.

LAUERYour caller makes a very important point. There are things that definitely work. And one way of remembering it is the ABCs -- aspirin inappropriate people, blood pressure control, cholesterol control and not smoking.

REHMWhat about obesity?

LAUERWell, obesity -- the relationship between obesity and heart disease is less clear than we have for blood pressure, cholesterol and smoking. It may very well be that obesity works through blood pressure and cholesterol. That's still on the area that requires a lot more work.

REHMDr. Michael Lauer of the National Institutes of Health, Duffy MacKay of the Council for Responsible Nutrition, from San Antonio, Shalene McNeill of the National Cattlemen's Beef Association, and earlier in the program, you heard from Dr. Stanley Hazen, chair of the Department of Cellular and Molecular Medicine at the Cleveland Clinic, thank you all so much.

LAUERThank you.

REHMAnd thanks for listening, all. I'm Diane Rehm.