(CNN) -- Her death made headlines around the world: Samantha Clowe, a 34-year-old British woman, died suddenly this fall from a previously undiagnosed heart condition. At the time of her death, Clowe was following a plan called LighterLife, a very low-calorie diet designed to help obese and severely obese patients lose weight.
She was consuming 530 calories a day.
"Samantha came to LighterLife with a BMI of 37, weighing more than 17 stone [238 pounds]," says a spokesperson for the company. "Although she managed to lose 3 stone [42 pounds], her health may have already been compromised." An inquest determined that Clowe most likely died from cardiac arrhythmia but could not determine what role, if any, Clowe's diet played in the development of her condition, only that her death "may be related to her low calorie diet and weight loss."
Very low-calorie diets have been used to help obese and severely obese patients lose weight for more than two decades. "Next to bariatric surgery, nothing is more effective for weight loss than a VLCD, including pills and other diets," says Dr. John Hernried, medical director for OTC Medical Weight Loss Group, a weight-loss clinic in California.
But the diet "is not indicated for someone who wants to lose 10 pounds." Most programs screen potential participants to ensure they are psychologically and medically stable enough to begin the process.
Gordon Heitman, 46, a California man, lost 233 pounds in just over a year on a VLCD that allowed him to eat an average of 800 calories a day.
"For the most part I wasn't hungry," says Heitman. "I was fine with what I was eating."
The diets use a process called ketosis to prompt the body to burn stored fat for energy while being fed anywhere from 500 to 800 calories a day. Patients may eat or drink only manufactured food, shakes, and snack bars especially created for and sold through specific programs. The products are designed to supply the patient with adequate nutrition without offering excess calories.
"This is a very specialized diet," says Hernried. " We are taking on full responsibility for [the patient's] nutrition."
In the United States, there are at least four certified VLCD diets, each run by a different company. Dieters enrolled in any of the programs purchase shakes, snack bars, and meal replacement foodpacks directly from the doctor or clinic supervising them. In the U.S., a day's worth of products usually has an average of 800 calories. Costs vary, but a year on a VLCD could cost between $6,000 and $10,000, if the person strictly follows the plan, which would include paying for program food and visits to the clinic to check in with the doctor.
"[These] are very safe and effective diets only if they are done under medical supervision,"says Hernried. "Not all VLCDs are made equal."
Hernried has lectured on very low-calorie diets for more than a decade and supervises a VLCD program in his California clinic. He believes every low-calorie program must have regular involvement from a medical professional and incorporate lifestyle changes, exercise, and enough calories in order to be effective and safe for the patient.
"I would never recommend doing a very low-calorie diet alone," says Hernried. Patients at his clinic have bloodwork done biweekly and get regular electrocardiograms.
"Absolutely these diets must be done under the care of a doctor," says CNNHealth.com's diet and fitness expert, Dr. Melina Jampolis, a physician nutrition specialist. "These things are not without risk."
Heitman says he is thankful for the medical supervision he received while on the diet. "My hair did thin out and there were other side effects," he says. "There were leg cramps ... and now they're monitoring me for gallstones."
Diets of less than 800 calories can lead to numerous complications, according to Jampolis, including heart arrhythmias, which could lead to death. Extreme dieters are also at risk of dehydration, electrolyte imbalance, low blood pressure and high uric acid, which could lead to gout or kidney stones, she says. Also, losing weight quickly could lead to gallstones and thinning hair because dieters are getting the minimum amount of nutrition, which can affect hair and bone density.
While different programs restrict patients to different calorie counts, Hernried believes some diets provide too few calories to their patients. "No matter how good the nutrition is in the product, the brain will start to break down under 600 calories."
On LighterLife, a patient with a BMI of 30 or higher is allowed four foodpacks a day, averaging 530 calories. LighterLife argues that its foodpacks comply with the United Kingdom's National Institute for Clinical Excellence and contain at least 100 percent of the recommended daily allowance of vitamins, minerals and trace elements. Before joining LighterLife, a patient must get approval from his doctor. However, once a patient is on the plan, the program does not regularly conduct bloodwork or EKGs.
"This industry of meal replacement, it can play a role for people with a lot of weight to lose, " says Jampolis. "But those people must be monitored by a doctor regularly and these diets must be part of a complete lifestyle overhaul."
Changing his lifestyle was the biggest challenge for Heitman. "Social events are all based around food, so you have parties at work, get-togethers, meetings -- almost at every social event, the center focus is food."
Behavioral counseling helped create new habits. "You're able to talk with other people on the program ... and they give you tips on how to do things. People who have been on the program a long time have their own tips to share."
"We will tell patients from the moment they come in ... the VLCD is purely a tool to get you out of medical risk," says Hernried. "The real work is not from the diet, it's the lifestyle changes."
"[It's] the follow-through with learning to eat right and regularly exercising," says Heitman. "I keep a food diary every day and I have found fun ways to get my exercise that ensures that I will want to get out and do it."
"I want to be around for my grandkids. I want to enjoy my life with my wife. It's about having that commitment."