MS. DIANE REHMThanks for joining us. I'm Diane Rehm. Fasting has been used for religious and spiritual purification for centuries. Now it's at the center of a popular new diet. A British physician and journalist joins me to talk about why he believes there's nothing else you can do for your body as powerful as fasting. His new book is titled, "The Fast Diet."

MS. DIANE REHMAnd Dr. Michael Mosley joins me from the BBC in London. If you'd like to be part of the conversation, give us a call, 800-433-8850. Send an email to drshow@wamu.org, follow us on Facebook or send us a tweet. Good morning to you, sir, it's good to have you with us.

DR. MICHAEL MOSLEYGood morning to you, Diane, great pleasure to be here.

REHMThank you. Dr. Mosley, I know a great many people in Britain, certainly, know about your diet. They've read about it, they've heard about it, they've seen how you've laid it out, but I'd like you to describe it for our listeners here in the U.S.

MOSLEYAbsolutely, because although it's described as a fasting diet, in fact, you eat on the days in which you fast.

REHMOf course.

MOSLEYSo what I'm aiming for is five -- I also call it the five-two diet because five days a week you eat perfectly normally and then for two days a week what you do is you cut down to a quarter of your normal calories. Which means for a man about 600 calories and for a woman about 500.

MOSLEYI do them on Mondays and Thursdays, but frankly you can choose any days. Do you want me to sort of describe what a 600 calorie diet looks like?

REHMSure.

MOSLEYSo what I do is I get up in the morning, I have a couple of scrambled eggs with a bit of ham. That's about 300 calories. I then drink black tea, black coffee, lots of water, herbal teas. I skip lunch and then in the evening, I eat a big pile of vegetables, broccoli or whatever and a piece of salmon, tuna, maybe chicken. And that's around another 300 calories and that is a fasting day.

REHMAll right, now I want to go back to a word you used. You said on the other five days you eat normally. Now, normally means one thing to one person and another thing to another. What do you mean by normally?

MOSLEYRight, what I mean by normally is doing whatever I would normally do if I hadn't actually started doing this particular diet. The reason I went in and started doing it was for health reasons, but it actually started with research which was coming out of the University of Illinois in Chicago.

MOSLEYAnd what they did was something called the alternate day fast and in that one you ate your 600 calories one day and then you ate whatever you wanted on the next day. And they thought that people would gorge, but actually they found on average people only ever compensated by increasing about 110 percent.

MOSLEYNow, what I mean by normally is I just eat with my family. If we're going out to a restaurant, I eat pizza. If we're at home, I eat whatever I would normally have done. And the importance of that is the problem with diets is that people get really bored with them and they're obsessed by calories. What is so psychologically attractive about this particular diet -- and I prefer to think of it as a lifestyle change, is that you don't think about dieting the other five days of the week.

MOSLEYNow, we're not suggesting you go and gorge, but equally I'm suggesting you don't obsess about calories because if you do that, then that will just make you obsessed about food and then you're probably going to crack up and fail. And that's why almost all diets, whether they are dietician's diets, doctors' diets, they all tend to end in failure because people become obsessed by calories.

REHMTell me what other health benefits you believe your diet, your way of eating offers?

MOSLEYRight. This is based on studies going back 20 years, mainly in animals, but more recently in humans. Studies based in Chicago also at the National Institutes on Aging and also in Manchester in England. And the different researchers were looking at different health benefits. So in Chicago, they were looking primarily at weight loss.

MOSLEYIn England, they were looking primarily at improvements in risk of cancer, particularly breast cancer. And at the National Institutes on Aging, interested in dementia. Now, the things that it has been demonstrated to benefit are diabetes because you get an improvement in your insulin and so those reduced risks of developing diabetes, it cuts your risk if you stay on it and lose about five percent of your body weight.

MOSLEYCuts your risk of breast cancer by about 40 percent. The dementia studies are being done primarily in mice, but the human trials are just beginning and Dr. Mark Mattson, who runs the studies at the National Institutes on Aging, is pretty convinced that he will see similar benefits and indeed his primary concern is dementia. So the ones you can say with some degree of certainty are that it will, if you stay on it and you lose body fat, that it will reduce your risk of heart disease, diabetes and some forms of cancer.

REHMDr. Michael Mosley, his new book is titled "The Fast Diet: Lose Weight, Stay Healthy and Live Longer with the Simple Secret of Intermittent Fasting." If you'd like to join us, call us on 800-433-8850. Everything you've said, Dr. Mosley, sounds fantastic. However, even in your own country, you've got some naysayers.

REHMYou've got Dr. David Haslam, chair of the National Obesity Forum who says, "As yet, there's not enough scientific evidence to confirm or refute the advocacy of this diet." He goes on to say, "It does not seem a natural way to eat and I doubt it's sustainable in the long term."

MOSLEYI must admit, I would expect nothing else because he is a very reputable scientist and reputable scientists always ask for more studies. There have been 11 studies to date and the longest running was 15 months, which is not bad for a study and all those studies have come out with consistent findings. They've also been done on around 400 volunteers have been through different varieties of intermittent fasting.

MOSLEYYou can't say that anything is ever proven, but certainly the evidence is pointing in that direction. He's wrong, I think, to say that this is not a natural way of eating. I think the way we eat now, eating five or six meals a day, is completely unnatural. The scientists behind it say that what you're really is you're going back to a period in which our bodies were forged and then we would've feasted and fasted.

MOSLEYFeast and famine were the norm for our remote ancestors. They would've eaten a lot and then they would've had periods without food. We, these days, eat every two or three hours. Our blood glucose levels are kept high, our insulin levels are high. All of these things are not terribly good for our health.

MOSLEYAnd so there is also a great deal of evidence of which he may or may not be aware, but that during periods of not eating, which I characterized as fasting, you see massive improvements in the health of mitochondria, enormous number of genes get switched on.

MOSLEYHousekeeping, basically, takes place when you're not eating and unfortunately we don't give our bodies a rest from food and that's kind of the argument behind it. There's a lot of biochemical, a lot of genetic evidence which supports this particular approach.

REHMDo you think there are any downsides of fasting?

MOSLEYI think if you go for a prolonged fast, there are serious downsides. I describe it fasting, but really I'm only talking about not eating for somewhere between eight and 12 hours, which is like not eating overnight, which is hardly the most arduous thing in the world. If you go for a three, four day fast a week or longer, then there are risks.

MOSLEYYour blood pressure may fall, you may feel faint. But that is, you know, a more extreme version and people in countries like Germany and Russia have had a long tradition of fasting. As you said at beginning, all the great religions have practiced fasting down the centuries and there's very little evidence it has done them any harm.

MOSLEYNow, I think there are a number of people who should not fast and these would include people who are type I diabetics, pregnant women, women thinking of getting pregnant and people who are pre-puberty. I think there is also, you know, just to be on the conservative side, I would not suggest anybody who has eating disorders or eating issues should be involved.

MOSLEYThere is no evidence that this triggers eating disorders, but just to be conservative. As I said, the great religions and the communities that embrace fasting like Hindus, Muslims, they're not the populations in which you see diseases like bulimia or anorexia. And so all you would say is if fasting triggered those things, why aren't they there? But I, you know, as I said.

REHMTell me, I wanted to hear about how you got to this diet yourself?

MOSLEYWell, about a year ago, I went to see my doctor and I was what -- I was having some moderate weight, 5'11". I was about 186 pounds so not terrible. And my doctor told me that I was a diabetic with a cholesterol off the chart. So he said, "You're going to start on medication." And I decided that wasn't what I wanted to do. I wanted to go and find a different answer.

MOSLEYSo I hooked up with a documentary crew and we went off looking for a different answer and I found intermittent fasting. On it, I lost 20 pounds of fat. So I'm currently 168 pounds and my fasting glucose levels now are completely normal and my cholesterol is completely normal. The other thing which we measured was a thing called IGF 1, which is a measure of cancer risk, particularly prostate and breast cancer.

MOSLEYAnd that went down from 30 nanomoles per meter which is basically at the top end of the scale, right at the top of the end. It halved and it's now 15, I'm right at the bottom of the scale. So on everything you could measure I improved.

REHMWell, you're a lucky man.

MOSLEYI am.

REHMAnd I'm sure we're going to hear from lots of folks who'd like to hear more. We'll take a short break and when we come back, we'll open the phones.

REHMAnd welcome back. On the line with me from the BBC in London, Dr. Michael Mosley together with Mimi Spencer. He's written a book about what he believes is a groundbreaking five-day, two-day diet. He calls it Five Two. It's the fast diet by fasting for two days out of the week and not completely fasting as we would think of it, but rather if you're female, reducing your calories on those fast days to 500. If you're male, to 600 plus lots of liquid.

REHMLet's talk about the liquid for a moment, Dr. Mosley. Does that liquid include not only water, tea, coffee, but diet drinks?

MOSLEYPersonally, no. I'm not a fan of diet drinks. I think the jury is out as to how bad they are, but I don't think they're good. Now some people who do it, they like diet drinks, the consumer diet drinks. I think that you need to retrain your taste buds so that you don't crave sugar as much.

REHMAll right.

MOSLEYSo I think that's quite important.

REHMHere's an email from Sally who says, "I've been on this diet since the turn of the year. I've lost 12 pounds. I don't feel deprived. I actually feel good about not eating so much on two days and definitely better not drinking alcohol." So I gather because of the low content of calories on those fast days, you must eliminate alcohol.

MOSLEYI would recommend it. You don't have to. I'm trying to keep the number of sort of commands down to a minimum, but I would recommend it. There's lots of evidence that not drinking for two days a week is also extremely good for your health, so it's a win-win situation. And there is quite a lot of calories in alcohol so if you can go without, I would recommend going without.

REHMNow someone else, Mauriel, points out, "Religious fasting also includes not drinking water during a fast." He goes on to say, "I assume the fasting you were referring to does not include skipping water."

MOSLEYIt does. I recommend drinking lots of fluid because you actually take in a lot of calories -- sorry, you take in a lot of water just from eating food. And I think clearly there are religious reasons for doing it, but the Prophet Mohammad also, in addition to Ramadan, suggested that you should cut your calories two days a week, and that was Monday and Thursday. And that's what I do for no particular reason except it seemed like a good idea.

REHMAnd...

MOSLEYBut one of the problems is that when you stop eating for a while what your body does is it reaches for the energy stores known as glycogen that is stored in your liver. And when that's released, water is also released. So you'll find yourself probably going to the loo a bit more and that's why it's important to keep hydrated.

MOSLEYAlso if -- quite commonly, you will mistake hunger for thirst. So I'm a big fan of drinking lots of fluid.

REHMHere's another email from Bradley who says, "On the day of fasting, does it matter when you eat the 500 calories?" He goes on to say, "You eat a small breakfast, then skip lunch and then a small dinner. Do you need this gap or could the 500 calories be evenly spread throughout the day?"

MOSLEYThere have been different trials. One of them was done on the alternate day fasting and three the subjects were just asked to eat one meal a day. They had to eat all their calories at lunchtime, but I think that was mainly for the convenience of the scientists. I tried that and I just found I got intolerably hungry. I like breakfast, so I decided to split it between breakfast and dinner, and also because I wanted to give my body maximal time without food.

MOSLEYThere have been other trials done in the UK, Manchester and those suggest that actually it's okay to spread them. The answer is we don't really know. What you have to do is come up with something that works for you. This is about -- as far as I'm concerned this is about a lifetime decision as opposed to a sort of brief hit and then over with.

REHMAll right. So you intend to stay on this diet?

MOSLEYWhat happened was that I lost 20 pounds on this diet, all of it fat. My wife, who's a doctor, said I would slow down now when I got down to about 166 pounds. And so I do it one day a week now, what I describe as a maintenance dose. So I just do it on a Monday and that has kept me at this level for nine months very comfortably.

REHMInteresting. And here's an email from Sean in Cincinnati who says, "I'm very interested in trying a form of the fasting diet, but as an active competitive athlete, I'm interested for health and religious reasons, but not for any significant weight loss. What general considerations should be taken into account for athletes who may be interested in aspects of the fasting diet?

MOSLEYI think the evidence is reasonably clear at the moment for the benefits in people who are obese or people who are overweight. The evidence in people who are already lean is not so clear. Now what I would suggest is that if you want to try it, you would need to look at some of the research evidence, because there is evidence that people who exercise in the fasted state burn more fat. And indeed there are other metabolic improvements which occur.

MOSLEYBut you'd need to compensate on the other days by ensuring that you ate adequate amount of calories because you don't want to kind of drop down.

REHMWhat about hunger, Dr. Mosley? Some people really get hungry during the day.

MOSLEYWell, there are two things. One is that if you eat a fairly protein-rich diet and a vegetable-rich diet which is what the recipes in the Fast Diet book are about, then you're much less likely to get hungry. If you eat eggs for breakfast with a bit of ham, I certainly find that keeps me full until 2:00 or 3:00 in the afternoon and then I drink tea and then I feel fine until 7:00 in the evening when I eat lots of vegetables. These foods are incredibly satiating.

MOSLEYThe foods that make you feel hungry are the carbohydrates. If you eat sort of croissants and cereal for breakfast, you're going to feel hungry by 11:00 or 12:00 because what happens is your blood sugar rushes up and then it crashes. And those are the things that trigger hunger. I think the first two or three weeks are quite difficult for some people, not for other people, because you're not used to, you know, not having a high sugar rush all the time. So it is a little bit of a struggle. But the dropout rate is in the first two weeks.

MOSLEYWhen you go beyond that, you'll discover that actually hunger is something which passes and that if you go out, distract yourself, go for a walk, many of the things you think are intolerable about hunger, they go. I can promise you you will not faint. You will not pass out on the floor. Your blood glucose will not collapse. Your body is fantastically good as long as you're not somebody like a diabetic. Your body's fantastically good at maintaining blood glucose levels. And it's just not going to collapse. These are one of the many myths that people have about not eating.

REHMYou know, one of the problems I've noted here in the United States and elsewhere is the incredible amount of food advertisements there are on television. They make food look absolutely delicious, mouthwatering. What do you say to those people who may be used to going to say McDonalds or Burger King and munching on lots of chips during the day and eating throughout the day? How do they begin?

MOSLEYI think that is a real challenge for anybody who lives in our society because there are always visual cues telling you to eat. Now one of the things I do is I don't have any chunk food in my house. Because if there's a bar of chocolate there there's a good chance I will eat it. So basically you have to clear the stuff out. Now when you're out on the street then obviously there is temptation.

REHMSure.

MOSLEYThe thing that I think works about this is you can say to yourself, I'm not going to eat that burger today but I can if I want eat it tomorrow. And then what I hope happens is tomorrow you feel less tempted. Or if you do feel tempted then you just eat it. That's fine. The thing that drives us is mainly habit. It's not that we're genuinely hungry or we genuinely want this or that. It's pure habit which dominates about 50 percent of our behavior. And it's driven by visual cues.

MOSLEYNow what you want to do is retrain your taste buds so you no longer crave fatty foods. And one way of doing that is by getting hungry and then satiating yourself with vegetables and with lean meats. And if you do that what will happen overtime -- or it certainly happened with me -- is that you will find that the things that, you know, drive your compulsions are no longer the burgers. They are the vegetables. Suddenly you want to eat vegetables because you have conditioned your body when it gets hungry to filling up on vegetables.

MOSLEYNow I used to tell people all the time, eat vegetables, but I never did it because I ate loads of junk. And when it came to my evening meal, I didn't want to eat the vegetables. I didn't feel like it. Now I actually crave vegetables. And when -- even on an ordinary day when I'm presented with a choice of a burger or the vegetables, generally I go for the vegetables because that is what my body has now learned to want.

REHMBut you talked about fish and chicken. You did not talk about beef.

MOSLEYAn omission. I'm actually a fan of beef as well, although I do think that broadly speaking the protein you get from fish and chicken is probably slightly better for you than the protein you get from beef. I do eat beef. I love roast beef. I eat it rarely. I do eat burgers, again rarely. I think the art of this is not to ban foods. It's to try and put yourself into a more positive frame of mind. Because what all the psychology teaches us is that once you think about things that you're banned from eating, they become an obsession.

MOSLEYIf I say to you, don't think about elephants, don't think about elephants, then all you can think about is elephants. And they have done studies like this. You just can't think about anything else. If you say, don't eat that donut, then I'm just going to think about donuts. So the art of this is not to think about negative things, but to think about positive things.

REHMAll right.

MOSLEYFive days a week you just do normal, two days you think, oh, I'm looking forward to that carrot. I'm looking forward to that bit of salmon. I'm looking forward to those delicious broccoli.

REHMAnd are you talking about home-cooked fresh broccoli, home cooked carrots or, as you well know here in this country and in your own, you can walk into a store and there are all these prepared foods, many veggies. But you're not really sure how many calories are in those prepared foods.

MOSLEYAbsolutely. I mean, I prefer home cooking. I do about a fair amount of cooking and my wife does a fair amount of cooking. And for me, it is a good reason to be in and to eat with my family so that I have breakfast with them, I have dinner with them. I simply skip the carbs, so I eat the vegetables and a bit of the meat. They eat the potatoes and the other carb-rich foods. And that's really the only difference.

MOSLEYI'm a huge fan of home cooking because then you know what you're eating.

REHMExactly.

MOSLEYAnd I'm also a huge fan of fresh vegetables because, again, we know that the sort of nutrients drop off pretty dramatically overtime. And you don't know when you buy food often whether that food is a day old or a month old, whether it's been kept in a refrigerator somewhere. And we know that the nutritional content drops off.

REHMAll right. And you're listening to "The Diane Rehm Show." Time to open the phones, 800-433-8850. Let's go to White River Junction, Vt. Good morning, Tammy. You're on the air.

TAMMYI'm interested in this because I do an Alzheimer's research study at Dartmouth-Hitchcock Medical Center in Lebanon, N.H. And one of my patients just recently, like last week, sent me an article on fasting and dementia, which I had not heard of. So I'm very interested in this.

TAMMYAnd the article talked about fasting while we sleep and -- because of the fact that fasting is uncomfortable for a lot of people and certainly for older people. And that they recommend that you just have an early dinner, maybe around 5:00 and then nothing after that until you wake up in the morning. And that that, while you're sleeping, is your fasting period. Can you mention anything about that?

MOSLEYNo, absolutely. Alzheimer's and dementia are incredibly interesting areas of research. And they are -- Dr. Mark Matson, who I write about extensively in the book because he's my sort of guru on this. He is the most cited neuroscientist in the world. More than 700 published papers. He works at the National Institute on Aging. And his interest is dementia because it is rapidly increasing worldwide.

MOSLEYAnd he did a study in which he looked at mice who were genetically engineered so they develop Alzheimer's. And he put them on a fasting diet roughly along the pattern I describe, which is kind of five, two. And what he found is that normally these mice developed dementia at around one year, which is equivalent of 50 in a human. Those put on a fasting diet developed it at around two years, which is equivalent to the 90-year-old, so right at the end of their life.

MOSLEYConversely those put on a junk food diet developed it at about three or four months. So he has discovered that when you go -- when you fast what happens is your brain produces a hormone called -- well, it's protein actually called brain-derived neurotrophic factor. And certainly in the mice when they cut their heads open they discovered they had developed 40 percent new brain cells in the area associated with memory.

MOSLEYAnd he thinks that BDNF, this protein, is neuro protective, that it protects you against developing Alzheimer's. It also makes you feel good. It is a natural antidepressant. So he is just starting human trials now in which they will be put on an intermittent fasting diet along the lines I've described, a five, two diet. And they will follow them for two years.

REHMBut...

MOSLEYThese are people who are at risk of cognitive decline.

REHMBut now...

MOSLEYNow I don't know...

REHMYeah, I was going to ask you to speak specifically to her point about fasting overnight.

MOSLEYI don't know, is the truth. I've never seen any studies on that. So I couldn't answer. I'm not aware of any animal or human studies that have been done in that area.

REHMAll right. And one thing I do want to ask you that you've already mentioned, the psychological benefits. What are they? How do they exhibit themselves?

MOSLEYI think they're at different levels. One is at the physiological level, which I've just described that actually your brain will start producing BDNF. That will make you feel better. The fact that you're not thinking about being on a diet for five days a week is hugely powerful. What people report to me as well is it enables them to break bad old habits. And we are, as I've said before, incredibly driven by habits.

MOSLEYWhat happens is you experience hunger for the first time and you realize you can tolerate it. You can live with it. So I think those are the main advantages.

REHMDr. Michael Mosley. His new book titled "A Fast Diet," all about the groundbreaking five-day, two-day diet. More calls when we come back. Stay with us.

REHMAnd welcome back. Joining me by ISDN from London and the studios of the BBC is Dr. Michael Mosley. He's written an international bestseller. Everybody in Britain knows about this, and probably the rest of the world as well. His book is titled "The FastDiet," in which he talks about eating normally five days a week, fasting on a total of 500 calories for female, 600 calories for men, twice a week. Here are a number of questions. First, Dr. Mosley, what about fruits? Which are high in sugar? Can they be eaten on this diet? Are some fruits to be avoided?

MOSLEYYes, they can be eaten. And although they're in sugar, if you eat them in the form of fruit, then the fiber in them will actually regulate your blood glucose levels. The thing you shouldn't be doing is really drinking fruit juice or smoothies because they are just a big sugar hit. The fiber is removed, most of the benefit is gone, so I wouldn't recommend it. Now, some fruits are very high in terms of their sugar hit. Things like bananas have a lot of calories in them. Things like apples, strawberries, as long as you don't have them with sugar are actually very low calories and pretty good for you. Grapes I'm afraid to say are just sugar in a bag.

REHMWhat about fruits like pineapple, cantaloupe, honeydew, watermelon, that sort of thing?

MOSLEYGenerally the sweeter they are, the more the calories, the bigger the sugar hit. I mean, I have no problems eating pineapple, but preferably not on days when you're trying to cut your calories.

REHMGotcha.

MOSLEYBecause what you don't want to do is you don't want to make your blood sugar shoot up. You want your insulin levels to keep down.

REHMAll right.

MOSLEYAnd so that's -- absolutely. So pineapple I wouldn't recommend. A lot of calories in pineapple.

REHMHere's an email from Tom in Charlottesville, "Should one be careful on the first day of fasting? I, for example, am prone to low blood sugar. I treat it by eating well balanced low glycemic meals six times a day. If I skip a meal, I don't think I could trust myself to drive safely. Do you think that would be a temporary problem or should I just not consider this type of diet?"

MOSLEYI think if you have issues with it, it's probably best avoided. I don't know whether there is any underlying medical condition, but most people do not need to eat six meals a day. And indeed the idea that if you do so this will somehow increase your metabolic rate is pure myth. What used to happen in the good old days 20 or 30 years ago is people ate three meals a day and they did not snack in between. And that is the big difference that happens now. The time between the meals has gone down and we consume more. And I think that has been a very regressive step.

MOSLEYI think people think they need to top up all the time. There is not a shred of evidence that this is good for you. And there's quite a lot of evidence that it's bad for you. But if that's something you find you cannot bear to do without, then I wouldn't be recommending trying this.

REHMAll right. And Copal writes, "I cannot find information on Dr. Mosley's site on lactating mothers and whether or not the fasting diet is safe while breastfeeding."

MOSLEYRight. I shall make a point of that. Because I do have a website called thefastdiet.co.uk and I shall write something about that. Broadly speaking, I am as conservative as I can be about this. And I think that one should wait until you have stopped breastfeeding. There's no particularly good evidence one way or the other, but you're going to be burning through an awful low of calories while breastfeeding. And I would wait until that is over and done with, and if you want to start then, by all means. But I think best not.

REHMAll right. Let's go to Chicago, Ill. Good morning, James.

JAMESGood morning. Thanks for having me.

REHMSure.

JAMESDr. Mosley, more interested in the foods that you're describing you're eating during your fast days and the actual caloric intake. From what you've implied, it's very closely adhering to a paleo diet, you know...

MOSLEYYes.

JAMES...high in proteins and vegetables and low in refined sugars. I guess first question and second point, why would you not adhere that daily? Is it simply a convenience factor and people getting discouraged with it? And then secondly, I would say -- sorry, go ahead.

MOSLEYNo, no. I mean, you're right. I mean, in a way a paleo diets mimics how our bodies were forged and there is a lot going for it. I however do not live in a sort of cave, if you like. And so I tried a paleo diet some time ago and I just couldn't tolerate it. I just missed all the other things I like eating. And so I need to go on something which I can sustain over a lifetime. There are plenty of people who've tried paleo and enjoy it. But I think it's probably too extreme for most people. And I was looking for something that most people could do. And I do think that most people can tolerate, you know, a sort of meat and veg diet two days a week. I'm not convinced they can do it for the rest of their life.

REHMSecond question, James.

JAMESActually second will be a point. For people, you know, wanting to adhere to this and just starting out I would say that -- and I think that you would agree, that convenience of food is a big factor, and ability to access it quickly and easily rather than cooking a meal if you're just trying to start on a diet, I would advocate the use of a crock-pot as, you know, high utility value for a diet like this where you can put in, you know, five or six chicken breasts and...

REHMOkay.

JAMES...low sodium vegetable broth.

REHMSure. What do you think?

MOSLEYSounds like a good idea.

REHMYeah, I think so.

MOSLEYThe recipes in the book are all really simple, to be honest. You can knock out quite a decent breakfast in about three minutes.

REHMAll right. Let's go to Houston, Texas. Good morning, Martin.

MARTINGood morning, Ms. Rehm. I love your show, try to listen to it every day.

REHMThank you.

MARTINNow, Dr. Mosley, I'm going to -- I've got a list that I've prepared rather than a long discussion about some of our food sources here in the United States and see if you have the same situation in the UK. For instance, fish, mercury and hydrocarbons. Meat and poultry, steroids, growth hormones, antibiotics. Fruits and vegetables, herbicides, insecticides, genetically modified organisms, a.k.a...

REHMOkay, Martin. Okay. I think we get the idea. Dr. Mosley, is that what you're focusing on?

MOSLEYAbsolutely not. I think these risks are all grossly overstated. And indeed there's quite of a lot of evidence that small amounts of poison are good for us. There's a theory going around called homosis, which suggest that indeed the poisons you find in vegetables are part of the benefit. So I think it is vastly better to eat vegetables even if they have some thin veneer of insecticide than not to eat vegetables. I'm really not bothered at all about those risks. I would much rather they didn't happen, but I'm not going organic myself.

REHMOkay. To Cleveland, Ohio. Hi, Mary.

MARYYes, thank you so much for your show and taking my call. I appreciate it very much.

REHMOf course.

MARYAnd putting science behind us, and I consider Dr. Mosley's work a huge public service to the whole world. I just wanted to put a human face on what he is saying, and not so much the fasting part, but what you said just -- I had to call because for ten years I started out on the South Beach, which I'm sure you're familiar with, because you decrease your carbohydrates and you do it initially quite extremely so that something happens in your brain, just as you said. And I no longer crave those things. I no longer crave carbohydrates.

MARYHowever, as Diane Rehm said, there are so many cues in our life, sometimes I will eat something like that just because I'm so conditioned over the years to do so, because I started this at the age of 50. But is there neurochemistry behind what you're saying? Because I truly crave vegetables and protein.

MOSLEYAbsolutely. I mean, one of the big areas of research at the moment is habits and looking at the neurochemistry of habits. And one of the things that happens is once you've got a habit, it never goes away. It always lurks there. All you can do is try and put a different behavior on it, so you get the same cues, but you behave differently. And the thing that drives habits is cravings. So if you can generate a craving by getting hungry and then satisfying that hunger with vegetables, in a relatively short period of time you will find that you actually crave vegetables.

MOSLEYIf however you get hungry and then you satisfy that craving by eating a donut and a couple of bars of chocolate, then that will just reinforce that habit. All the reward pathways in the brain will be built up.

REHMHow long...

MOSLEYAnd the problem with...

REHMI was just going to ask how long you think it takes to break that craving habit.

MOSLEYI think it's very difficult to say and it's probably individual. With me it took about four weeks. The truth is that people have this sort of idea that if you stop eating sugar for three weeks, then that'll be it. There is no evidence of that whatsoever. Once the habit is there, it is there for life. What you have to do is find ways of subverting. So I still eat donuts occasionally, you know. The main thing is don't feel guilty about it. Obviously don't go and do it again if you can avoid it, but willpower is grossly overrated.

REHMAll right.

MOSLEYReally grossly overrated. We beat ourselves up for being weak. And the reason why diets fail is largely down to all sorts of things going on in your brain which you have very little control over.

REHMAnd here's an email from Alicia, who is a physician and public health researcher at Johns Hopkins University. She says she recently became almost exclusively vegan based on research she's been reading related to consumption of animal proteins to cancer and other chronic illness. Does your guest feel his diet affords additional or different benefits? Can his diet be done as vegetarian or vegan?

MOSLEYAbsolutely. And one of my experts, Professor Valter Longo, who is an expert in the diseases of old age and he's based at the University of Southern California, he would absolutely endorse a vegan diet if you can do it. Now, interesting that she's at John Hopkins because that's also where Professor Mark Mattson is based along with National Institute on Aging. And there is a lot of evidence that a rich protein but mainly vegetable diet is incredibly good for you. And vegans, for example, we know that they have much lower levels of inflammation. And inflammation is associated with arthritis, all sorts of other conditions.

MOSLEYNow, I cannot bring myself to be a vegan. Just I've had a go at that as well and I just missed meat. But I am reducing the amount of meat I eat and I am reducing other things. I think if you can move in that direction, then there are undoubtedly a lot of health benefits. But you obviously have to make sure you're getting adequate amounts of other essential nutrients which you will not get in a vegan diet. So you have to approach it cautiously. But, you know, if she's doing well on a vegan diet, then that is marvelous.

REHMAll right. Let's talk about practicality, how to get started. You've talked about measuring each part of your body.

MOSLEYAbsolutely. What I did before I started was obviously I got on the scales to measure my weight, but I also got on a pair of scales which measure your body fat. You can buy those quite easily, so you know what your body fat is like. You measure your waist, because you're waist is your best predictor of future health or ill health. It's the best predictor we have of who will develop diabetes and heart disease. Your waist which is measured around your belly button. It is not your (unintelligible). It's the belly button. That should be less than half your height. So if you're 6 foot, it should be less than 36 inches. You should also probably have your fasting glucose measured and your cholesterol, by which I mean your LDL. All of this is in the book.

MOSLEYAnd there's also a more exotic test which is the IGF-1. So you start off knowing what all your measures are and then you just follow the diet. I mean, as I said, the book is full of recipes. And the best thing is also to go and visit websites where you can get information, and ideally do it with somebody else, because it's best done publicly, with somebody else. You'll get support. And people enjoy talking about it. They're also incredibly generous. I found -- I have a website and people are incredibly generous about sharing their tips, their help, their encouragement and things like that. And then hopefully what you'll see is...

REHMAnd I think everybody in my office is going to do it, so we'll be sharing that information. And you're listening to "The Diane Rehm Show." Let's take a caller in Jamesville, Wis. Denise, you're on the air.

DENISEGood morning, Diane. It's really nice to talk to you and the doctor.

REHMThank you.

DENISEThis is a practical question. Although I'm well-hydrated but not over-hydrated, I find that when I go three to four hours without food I feel nauseous. Some indigenous cultures (unintelligible) that with say sucking on a peppermint candy. What would be the doctor's solution to that? Thank you.

MOSLEYI think try things like that. Ideally sugar-free. I would drink lots of green tea and I enjoy sort of herbal teas. Again, zero calories. And if the nausea persists, then I would also take to eating some vegetables, you know, carrot sticks. A little bit of low calories vegetables will not do you any harm at all, I don't think.

REHMI would gather the diet industry is probably not too happy with your plan, Dr. Mosley. What have you heard?

MOSLEYI think one of the things, as well, is you're going to save quite a lot of money, because you're going to be eating less lunches, which means you'll save money there, and your grocery bill will go down considerably. So I am absolutely not endorsing any form of diet related foods, because I think they're all nonsense. I think the things you'd buy out there which are sold by the diet industry are on the whole a con. So I think the people should eat well healthfully, but just less two days a week.

REHMAnd if in fact they gorge the other five days a week, how's that going to affect dieting?

MOSLEYI think that if that happens then you're extremely unlikely to lose weight. There were studies done using what's called alternate day fasting, and which people did gorge, and on the other day they ate their 500, 600 calories, and they still lost weight. But that's because it was a more extreme version of intermittent fasting. I suspect if you gorge, you're not going to lose anything, and you're probably going to get limited benefits.

MOSLEYIf you find that you're doing this and you're not losing weight, then you should, first of all, look at your liquid calories, which is orange juice, smoothies, alcohol, on even your non fasting days. And the other important thing would be to keep a diary. But initially I would recommend don't think about it, don't gorge, but don't worry about it, just get on with your normal life.

REHMDr. Michael Mosley, together with Mimi Spencer, he's written "The FastDiet," all about the groundbreaking five day, two day diet. Thank you so much for joining us.

MOSLEYAbsolute pleasure.

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