Last winter, Natalie Vargas was nearing her mid-30s, eating fast food for lunch, drinking about nine cups of coffee a day, and feeling exhausted and sick to her stomach. But all of that changed in April 2015, when she began following a program she heard about on Facebook from a friend who had been struggling with similar issues.

“My body started to feel better and better and better,” Vargas, an aesthetician who lives in Newburgh, N.Y., told FoxNews.com.

Vargas, 34, credits the transformation to a $125/month weight loss and cleanse program she purchased through Plexus. The company is one of countless that uses multi-level marketing (MLM)— a trend that experts say has helped fuel the U.S. dieting industry’s growth to an estimated $64 billion value, the latest data available from research firm Marketdata Enterprises.

As New Year’s resolutions to hit the gym and eat healthy begin to wane, droves of Americans like Vargas will turn to similar programs that suggest their brand-specific supplements can help kick-start users’ metabolism, detoxify their systems and boost their energy.

Many people will learn about these programs through friends on social media who are then compensated by the company whose products they’re promoting— the basis of MLM, or network marketing.

But due to flexible federal regulation of weight loss products and their often obscure ingredients, many registered dieticians question whether these programs offer more than what can be attained through a traditional healthy lifestyle. Others worry some may be Ponzi schemes that could leave participants not only sicker— but also broker— than when they started. 

Can you really “detox” the body?

On Amazon, nearly 3,000 products are listed under the subcategory “Detox & Cleanse.”

“The terms ‘detox’ and ‘cleanse’ have become so mainstream in the dieting world that those terms don’t mean too much anymore,” Heather Mangieri, spokeswoman for American Academy of Nutrition and Dietetics and a registered dietician nutritionist (RDN) based in Pittsburgh, told FoxNews.com.

But if you talk to anyone with a degree in dietetics from an accredited university— like Mangieri, who received her master's degree from the University of Pittsburgh— or any biologist with similar credentials, they’ll tell you the same thing: The body already cleanses itself. That’s what the liver, kidneys and colon do naturally.

“If [cleanses] ever did the kind of thing they’re claiming to do, they’d kill you,” Michael D. Gershon, a pathology and cell biology professor at Columbia University, told FoxNews.com.

Gershon, who studies the bowel’s relationship with the nervous system, said the bacterium in the body’s colon lining plays a fundamental role in digestion and nourishment. For example, cellulose, a component of fiber found in leafy greens like lettuce and spinach, can’t be digested by the body without the delicate balance of bacterium that self-regulates in the colon.

When the colon absorbs toxins— by way of exposure to a foodborne illness like salmonella or cholera, for instance— the body becomes nauseated and vomits to try to rid itself of that toxin. In foods that are safe to eat, toxins aren’t absorbed. The body flushes them naturally.

“One way to avoid a toxin is don’t eat it,” Gershon said.

Taking any supplement in excess has the potential to have the opposite of its desired effect— that is, overloading on supplements may intoxicate the body, said Samantha Heller, a senior clinical nutritionist at New York University’s Langone Medical Center.

Heller, a registered dietician for nearly two decades, referred to Nobel Prize winner Linus Pauling’s 1969 theory that vitamin C was a “miracle” supplement that could cure the common cold and extend people’s life spans. Following that belief, which has been debunked multiple times but is still popularly held today, people began taking too much vitamin C, causing the vitamin to transform from a disease-fighting antioxidant to a pro-oxidant, Heller said.

“Our bodies are designed to deal with these vitamins in teams,” Heller told FoxNews.com. “[Vitamin C] works closely with vitamin E and selenium to balance the body’s system, so too much of one or the other can really knock it off. So in addition, you may be overloading your body’s ability to metabolize and detoxify these supplements, overwhelming your liver and kidneys.”

“We don’t know what large doses of these supplements may do to our bodies,” Heller said.

Can supplements help you lose weight?

Popular programs like Plexus, as well as Isagenix, AdvoCare and Arbonne, call for taking supplements, either in pill or powder form, and some version of fasting from whole foods.

Heller hasn’t extensively studied the ingredients of products in those plans, but she said a quick review suggests many contain Stevia, a non-nutritive sweetener that research suggests may “interfere with the gut-brain axis, increase sweet cravings and appetite, and shift the gut microbiome in an unfavorable direction.” The microbiome refers to that crucial population of bacterium that Gershon described.

Heller said some of the products for these programs also contain laxatives.

“Looking at the long lists of ingredients in these products, one wonders, ‘Why not just eat real food, where Mother Nature has created the perfect balance of nutrients for the body?’” Heller said. “These kinds of programs are a waste of time and money.”

Isagenix, a company that has about 230,000 likes on Facebook, has a whole catalog of packages not only for weight loss, but for performance enhancement and energy, among other solutions. Its 30-Day Cleansing and Fat Burning System calls for, during two different periods throughout the cleanse, an elimination of full meals and taking a mix of shakes and supplements the company says may “accelerate” weight loss, as well as “cleanse” and “flush” the body.

AdvoCare, which has about 374,000 likes on Facebook, has a 24-Day Challenge that features a bundle of supplements to be taken during a 10-day cleanse phase to “rid your body of waste,” among other effects, and then offer “appetite control and overall wellness” during the following 14-day phase.

Whether it’s helpful at all to supplement a healthy, balanced diet with any vitamins and minerals in the first place is unclear, registered dieticians say.

Although sales of supplements have led to the growth of a multibillion dollar industry, the science behind whether they’re helpful or harmful— or do nothing at all— is fuzzy.

Studies on multivitamins, for example, have produced mixed results, with some research suggesting people who take them may be less inclined to follow a healthy diet— thus increasing their risk of early death— and other studies suggesting they may extend an individual’s life span.

Some experts say individuals could benefit from taking a vitamin D supplement, Heller noted, but the popular belief that vitamin B12 can offer an energy boost is a myth because the body excretes the vitamin before fully absorbing it.

A big reason why companies can say their products may have certain benefits lies in terms laid out by the Federal Trade Commission (FTC). Those rules outline what dietary supplement companies and their ambassadors may imply during marketing, but they allow companies to clarify claims with asterisks that indicate their products may not work for everyone and that they are not approved by the Food and Drug Administration (FDA).

Since 1994, when Congress passed the Dietary Supplement Health and Education Act, supplements—whether sold individually or bundled in weight loss packages— have been freed of regulation from the FDA.

“It is the company’s responsibility to make sure its products are safe and that any claims made about such products are true,” Lynsday Meyer, an FDA spokeswoman, told FoxNews.com in an email. “But just because you see a supplement product on a store shelf does not mean it is safe.”

“The FDA has received numerous reports of harm associated with the use of weight loss products, including increased blood pressure, heart palpitations (a pounding or racing heart), stroke, seizure and death,” Meyer said. “When safety issues are suspected, FDA must investigate and, when warranted, take steps to have these products removed from the market.”

To Heller’s knowledge, there is no supplement that has been scientifically proven to expedite weight loss. 

“There isn’t any,” Heller told FoxNews.com. “[Weight loss] has to do with how much physical activity you do, and how much calories you burn and how much you take in, and it’s really as simple as that. But the quality of those calories counts.”

Heller and Mangieri both said two-day cleanses that call for consuming only juice may help someone get into a proper mindset to jump-start their weight loss goal and, depending on the plan, leave them properly hydrated. But for any time beyond that, these types of juice cleanses can be dangerous.

“If you’re not consuming food that has some protein and some carbohydrates and some fats over a period of time, then you are scaring your body,” Heller said. “And so it launches into this urgent mode, and why would we want to do that to our bodies, which are dealing with enough difficult stuff as it is?”

Mangieri said any safe program would include the basic foundation of a nutritious diet: fruits, vegetables, lean protein, whole grains and healthy fats.

“Any program that’s avoiding certain nutrients is a huge red flag— also programs that claim that they’ll help you lose weight in a certain amount of time,” Mangieri told FoxNews.com.

Depending on a person’s starting weight, generally speaking an individual can lose 2 pounds a week with a healthy eating plan and without supplements, she said. “That’s 8 pounds a month, which is really good."

Vargas, the Plexus participant, said she lost 8 pounds on the company’s TRI-PLEX Combo, which consists of a powder to be mixed into water, plus two solid supplements. Now expecting her first child, she has continued taking the combo each month and said the healthy track Plexus has put her on helped her keep off the weight until her second trimester of pregnancy. She also credited the program with helping her conceive, which she’d had trouble doing prior.

Vargas cleared the TRI-PLEX Combo with her OB-GYN and communicates on a private Facebook page with about 10,000 other women who are pregnant  or trying to conceive while taking Plexus products. She said she’s working on becoming an ambassador for the program by sharing personal testimonials with her friends in hopes of recruiting new participants on Facebook. With that rank, she’ll get the TRI-PLEX Combo for $109 a month instead of $124. She’ll have to make that $109 monthly quota, either through sales to other people or with her own purchases of Plexus products.

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Is your diet worth the price?

In programs that operate under MLM marketing, participants hear about the product at hand through an ambassador or distributor who sells them the product then acts as their adviser throughout the program, like the relationship between Vargas and her coach.

While legal MLM companies can resemble fraudulent pyramid, or Ponzi, schemes, it is likely legal if it meets certain criterion outlined by the Securities and Exchange Commission (SEC). According to the SEC, pyramid schemes and legal MLM companies both suggest participants can profit when they recruit new followers and often require a “buy-in” or fee of some amount to become a seller. Kaitlyn Iannuzzi, Vargas’ coach, said the sign-up cost to become a Plexus ambassador is $150, which includes the ambassador’s first month of products.

Some of the key characteristics of pyramid schemes are that they don’t offer a real product, promise a “get rich quick” model with little to no work required, and have a complex commission structure, according to the SEC. While some of the commission structures of popular cleanse programs could be considered complicated, companies like Plexus, Isagenix and AdvoCare do offer products and require their ambassadors to actively recruit new members to earn money.

The SEC monitors those companies that are publicly traded, while those that are privately owned may list their financials online.

Depending on his or her level and the program at hand, an ambassador for a popular cleanse program can earn between about $700 to over $1 million per year. The aim is that the more they sell, and the more people they recruit, the greater their earnings.

Laura DeAngelis, a 41-year-old personal trainer based in New York City, bought a supply of Isagenix’s 30-Day Challenge products last February and talks openly about her experience, but she isn’t an official, paid ambassador for the company.

DeAngelis said she felt the program helped kick-start her metabolism and lose problem pounds she wasn’t able to shed on Weight Watchers, a program whose tenets she has followed since 2004. When all was said and done, she lost 10 pounds in 30 days, and the program’s rules against consuming caffeine, alcohol and processed foods helped her refocus on what she was putting into her body afterward. DeAngelis said she paid about $300 for the 30-day supply of Isagenix products.

“Some people may look at the price tag and say, ‘That’s a lot of money,’” DeAngelis told FoxNews.com, but “when I broke it down, it was fiscally responsible for me, so I think people need to sit down and see what they’re spending on junk food and other things.”

“For me, it was [worth it],” she added. “It was an investment for my feeling better.”

Iannuzzi, Vargas’ Plexus coach, would not disclose how much she earns as an ambassador for the company, but she said that income covers her student loans and mortgage in Orange County, N.Y. Iannuzzi, who is 30 and lives in Greenville, said she’s on her way to becoming a full-time ambassador for Plexus.

“I’m so passionate about the company,” Iannuzzi, currently a nuclear medicine technologist and a bartender, told FoxNews.com. “When you believe in something and believe it works, you want to share it with the whole world.”

Mangieri has met people like Iannuzzi who are ambassadors for cleanses because they support the product they’re promoting, but she said the absence of their formal education and certification in nutrition and dietetics concerns her.

“It’s not safe, and unfortunately the knowledge is not there to be teaching proper nutrition,” Mangieri said. “I don’t want to put out that these people selling it don’t care because I’m sure some of them do care about helping others,” she added, “but it is a business, bottom line. It’s about making money and getting other people on board.”

Both Vargas and Iannuzzi said they know Plexus’ products aren’t FDA approved, but that doesn’t concern them.

“No supplements are FDA approved— whether it’s the vitamins you’re taking, the protein shakes you’re taking, even the probiotic your doctor is prescribing,” Iannuzzi said. “I knew people in the health care field using these products and selling these products.”

Heller, also the author of “The Only Cleanse,” which outlines a 14-day cleanse based on whole-food and lifestyle choices, said one of her biggest qualms with many popular or fad cleanses is their lack of sustainability.

“[These programs] take the decision making piece out of it, and then the person doesn’t have to think about what they’re eating, they don’t have to plan ahead, they don’t have to cook, they just have to follow the program, and for some people that can be attractive for a short period of time,” she said. “But the reality of it is life happens … and then all of that goes down the tube because the person has not learned the strategies they need to manage real life.”

“Real life is a rollercoaster,” she said. “We keep hoping it’s going to be a nice, smooth easy ride, and for the most part it’s not. So we want to learn how to manage that in mind, body and spirit in a way that helps optimize our health and our coping skills.”

But for Vargas, Plexus’ TRI-PLEX program has done just that— in a way that no other approach she’d previously used had.

Last spring, after being hospitalized for irritable bowel syndrome, doctors discharged her with an antacid prescription. Vargas returned to her poor eating habits and her digestive issues returned. She then tried a 10-day, $250 celebrity cleanse that included shakes, multiple probiotics, and only an organic apple for whole food.

“You were literally starving yourself for 10 days. It was cleaning me out, but then I still felt like crap,” Vargas said. “So I started working out. Then I changed my workout regimen and did weight lifting to give me some energy or something. Nothing was working for me, not until I tried Plexus.”