tonight on "nightline," fad diet danger. tis the season for serious eats. and that means big business for weight loss products. but today, the fda suddenly calls one diet potentially dangerous. we break down what you need to know about america's favorite diet. murder, she wrote. she's the reigning queen of the american crime novel. tonight, patricia cornwell takes us inside her favorite forensics lab and we hit the skies with this criminal mastermind. and treasure hunters. gold, coins and the obsessive sleuths who cross the globe for a shot at a big score.

we'll show you them. >> announcer: from the global resources of abc news, with terry moran, cynthia mcfadden and bill weir in new york city, this is "nightline," december 6th, 2011. >> good evening, all, i'm bill weir. well, there are 60 billion reasons to get into the weight loss business. that's mow many dollars we the people spend each year in the struggle for a smaller silhouette. but all the fad berries, roots and hormones lead to a staggering number of americans getting ripped off, sick or both. today, the fda pulled one wildly popular group from the shelves. don't, we survey what other diets are popular and how they perform. here's abc's sharyn alfonsi. >> reporter: it is a holiday tradition. big meals, batches of cook keeps, endless cocktails and then -- scale shock. tis the season for weight gain. and then almost immediately, a desperate attempt to lose it.

cue up the diet du jour. fad diets sprout as fast as weeds and wither away just as quickly. yet, they all offer the promise of the same thing. a quick fix to fat. but do these diets work? and more importantly, are they safe? for gam pl, today, the fda announced the first step in bank the sale in the ingredient used in the so-called hcg diet. >> when you put them under your tongue, you basically feel a little bit of a burning sensation. >> reporter: victoria is an hcg devotee we interviewed earlier this week. the hcg drops sue press your appetite. >> you either do it for 23 dames or a maximum of 40 days. i can do anything for 23 days. and if i can lose 15 pounds, why not? >> reporter: now, the fda has ordered all products removed from the market, saying the products are unproven to help

with weight loss and potentially dangerous. but there is no short ablg of other diets to dabble in. and so we assembled a pattern of the top dietitians. on a rating scale of 0 to 5, 0 being the worst and 5 being the best, we asked the experts to rate all the most popular diets today. >> it's almost as if the more ludicrous a diet sounds, the more attractive it becomes. >> reporter: and so many of them are tied to the stars. from moms like mariah and j.lo like brides to be and not to be, like anne and kim. we see celebs drop sizes and want to know what's their secret, buying into the idea that their abs, butt, legs can be ours if we just take the drops, these pills or eat from that jar. >> sounds so good and there's the promise. you follow these rules and you get this result. it's hard not to be pulled in.

>> reporter: and it's that mentality that fields into the diet industry. a million billion dollar industry looking to market the latest craze or recycle about a old one. >> the new fad diets are the same as the old fad diets. >> reporter: last fall, jen for aniston found herself as the accidental face of promotion for the baby food diet. >> celebrities know they've lost weight. >> reporter: and don't forget the celebrities have personal chefs, air brushed photos and private trainers who customize their every meal. people like tracy anderson. the trainer to the stars was rumored to have been urging clients to eat baby food. she has sung the praises of pure rayed food. she never intended people to go gaga for gerber. >> i had baby food companies, like, wow, our baby food -- i'm like, are you kifding me? >> the baby food diet, i would give it a 3 for effectiveness.

because that's because you could still even with baby food, overeat. >> reporter: tracy says she's experimented with dieting. >> i was raw food for seven months and i lost my menstrual cycle. >> reporter: the raw food diet stirms up a difference of opinion. >> the raw food diet, as far as nutrition, i give it 5. >> my rating is 0 for the raw food diet because it is potentially dangerous and deficient in many knew treatnut. >> reporter: the positiat diet raw, all the time. >> the average american is not eating enough fruits and vegetables. >> reporter: following up on that path is the caveman diet. actress megan fox is the celeb rumored to be a fan. >> i like the caveman diet. i would give it a 4. >> reporter: raw fruits, vegetables and maepts. >> in today's world, you can't

eat like a hunter and gatt erter if you are sitting on the couch. >> reporter: at the fore front of pegged fads for 2011 is the dukan diet. a protein-heaven i have diet in four phases. >> as far as effectiveness, i give it a 4. >> very trendy. think it gets very confusing with all the cycles and phases and i think for the average person they could get a little lost. >> reporter: j.lo is said to have used that diet to help shed baby weight. and tabloids report it's the secret behind pippa middleton's royal asset. but with some of the worst eating habits in the world, are americans really ready to trade in their love affair with decadent treats, fat-laden golden fried irresistible greasy goodness for a real commitment? >> if you really want to change your relationship with food and you really want to get results that are going to last, you need more than a fad. >> reporter: it really boils down to just a simple question. are you willing to give up these

buns for those buns? for "nightline," i'm sharyn alfonsi in new york. >> founder of an hcg sales site, the original hcg drop.com, responded to the fda's move by telling us, quote, obviously our mission to help people with weight loss will be different but it's not going to end. end quote. and our thanks to sharyn alfonsi. coming up, we see drops of blood but she sees the whole murder. even hears the screams. one reason why she is one of the most popular crime novelists in the world. ♪ [ male announcer ] you'd be shocked how much data you use in a month. e-mail, status updates, finding your way, uploading photos, downloading an app, an app, and another app. kilobytes, megabytes, gigabytes... all stacking up until you reach your limit. and what happens if you go over? with sprint, you don't have to worry.

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after you take it off. can your patch say that? for up to 16 hours of relief... try thermacare. >> announcer: "nightline" continues from new york city with bill weir. >> a lab tech peering into a microscope. not exactly the stuff of

pulse-quickening drama, unless you're one of the millimeters of fans of today's most popular crime shows. the science of splatter patterns and forensic decay is now much more sexy than any old cop show. and tonight, my coon abo-anchor the best-receiving crime novelist who was the first to see that potential and she has a few scary things to show him. >> reporter: i'll get in the back. this isn't exactly the most likely place to interview a crime novelist. but for patricia cornwell, one of the best crime writers ever, flying her own hall continuer is all part of the thrill. >> this requires a certain amount of skims with your dexteri dexterity. you don't want to fly it, you want to think it. a very fills of skal machine that way. >> reporter: our destination? the body farm at the university of tennessee, where for three decades, forensic scientists have studied the decomposition of human remains. a crucial field for crime solving. at any given time there will be

several bodies and they're examining the decomposition of them? >> the decomposition, what insects and birds do, what weather conditions, whether the body is in the shade or in the sun or it's in water. >> reporter: grim work, perhaps, but for cornwell, it is the work of heroes. more than any other crime writer, cornwell has hearalded work of forensic investigators. the crime scene technicians and medical examiners who solve cases by search iing for tiny clues in the grit and blood and fibers left behind by killers. >> i didn't invent forensic science medicine. i was one of the first people to realize how interesting it is. >> reporter: her greatest invention is dr. kay scarpetta, the main character in 19 of her novels, including the latest one, "red mist." >> when scarpetta is in charge, you are going to be fine. and when she leaves the scene,

then it's not safe anymore. >> reporter: how did you come up with her? is she you? >> no, because i dropped chemistry. i practically blew up the lab in college. >> reporter: i confidence, her sense that you're safe with her? >> i think that some of that is me. but there are things about her that are wishful thinking on my part. she's a doctor, she's a lawyer, she's a radiology expert. she does these things for real. i simply write about them. you want to be so good that you have a tight pattern right there. >> reporter: and that's why we're here, not far from the body farm, at the national forensic academy in oak ridge, tennessee. a premiere training ground for forensic investigators from around the country,y cornwell is a major benefactor and a perpetual student. we donned protective gear to take a close look at how blood spatter evidence is analyzed. >> you can tell when someone stomps on a body or hits somebody with something hard and

blood flies out. all telling -- it's all screaming in its own way. it's screaming, what happened, look what you did to me. >> reporter: first, a baseball bad and real human blood. nicely done. he's dead. >> wow. see? now, one thing i'll show you right away. if you look at these droplets, you can see the direction that they're going. ready? >> reporter: then, the hammer. >> that's interesting. very different pattern. you have a different size object doing it. but still, you have these high velocity droplets. >> reporter: watching cornwell here, it's almost as if she's channeling kay scarpetta. >> like an accident? no, i'm counting x number of bloches. the blood items the truth, even if you don't. i'm going to tattle on you. >> reporter: blood doesn't lie. everywhere we go here -- >> see how it opens up? >> reporter: ballistics,

fingerpri fingerprints, old guns and knives. >> this would not -- i don't mean to be gross, but this would be a good knife for cutting someone's throat. >> reporter: cornwell is in her element, passionate to learn how bad guys kill and good guys catch them. and when did it occur to you that all of this evidence would make for great story telling? >> when i was a crime reporter for the newspaper, i thought it made for great stories. that's what i chased after. it was always the unusual twist or the slant or the ah-ha moment, as you say, where there's one little thing, the devil in the detail that changes everything. i always want that one detail. >> reporter: all across the screen these days, big and small, you can see cornwell's influence, in shows like "csi," "dexter" or "criminal minds." hugely successful shows. and that clearly rankled her. >> i was shocked.

why didn't someone think of this while we had a chance? but my property back then, we're talking really the '90s, was all tied up in movie options. so, yes, there was -- there were some moments where i thought, wow, you know, my time came and went. and any adaptation of my material has already been done by everyone else. >> reporter: you know, that would surprise people. you are one of the most successful authors in the world and you feel, at one point, you felt, i missed the boat. >> i did feel that. i don't think it's over. when it happens, it will have been worth waiting for. >> reporter: in fact, angelina jolie has signed on to play kay scarpetta in a film now in development. >> is that my helicopter i hear? >> reporter: that's pretty cool. >> reporter: and for her legions of fans, it can't hit theaters too soon. on the side of her helicopter, cornwell has 'em blazened kay scarpetta's sale, which she designed. a tribute to a character who has taken on a life of her own for

millimeters of readers and for patricia cornwell. >> you know what when she appears on the scene, no matter what state she's in or what chaos abounds, some how she's going to make it better. >> reporter: you like her? >> i do like her. i wish she would walk into this room, because i would love to be her friend and i think my heartbreak would be if she walked in and looked at me and didn't know who i was. >> cornwell's new book "red mist" is in stores now. our thanks to terry. coming up next, what is it like to join a band of globe-trotting treasure hunters in a search for one big find? oh, hello. i'd like to tell you about netflix. it's an amazing service that lets you watch unlimited movies and tv episodes instantly. you watch netflix on your pc or on your tv through a game console or other devices, connected to the internet. wow, that's fast. best of all, netflix is only... [ buzzing ]

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most imagine the metal detector set as the guy on the beach tossing sandy change into a coffee can. but there is more serious booty to be had out there, for those with the patience and the detector-swinging technique to find it. and for nick watt, hard core treasure hobbyists are a "sign of the times." >> reporter: gigantic hoorlds are lurking under these english fields. buried treasure. two years ago, one hunter found a multimillion dollar stash of an schent gold. here, another guy found 53,000 roman coins. >> go both ways, you say okay. >> reporter: so, i took a crash course in metal detecting. >> i know a line this way. and in your mind you make a cross on the ground. >> reporter: this brotherhood

with buzzing in their ears call themselves detectorists. these guys come all the way to england in search for treasure. >> there should be a date -- >> reporter: 1701. >> this is something that i'm not sure of. >> reporter: a couple of years ago, they had to tell one old timer to hang up his detector. >> he was 91 when we said it was, i think, too much. >> reporter: he was bringing girlfriends? >> yeah. he brought his girlfriend. he brought her twice. >> reporter: without any such distractions i was still struggling even in this field which was, for centuries, a busy port, bustling with romans. i think i'm missing what you need to be a detectorist, which is patience. patience and luck. you look happy, mike. mike martin oozes good fortune. >> i just found this. >> reporter: oh, wow. >> a complete spoon. >> reporter: maybe 600 years old. >> i get goose bumps when i find things like this. >> reporter: really? >> i got them now.

>> reporter: and here's the most amazing part of all. mike, like most of these guys, just givens his treasure away. to museums. >> i don't sell anything. >> reporter: you don't sell anything? >> nothing. >> reporter: whatever i find, i'm keeping. i heard a noise, dug a hole, got excited. what is it? just a piece of junk iron. you might 50 or 60 pieces of junk before you find a keeper. maybe next time. just maybe. i'm nick watt for "nightline," still searching, in norfolk, england. >> keep looking, nick. and we do invite you to tune into a very special edition of "nightline" tomorrow night. major network exclusive. abc's barbara walters traveling to damascus to interview bashar al assad. the first time he's spoken to american media since the bloody uprising that began against him nine months ago. that's a special