Should You Try ProLon, the Popular Fasting-Mimicking Diet? We Asked Dietitians

Woman drinking tea ProLon diet
Woman drinking tea ProLon diet

The simple act of fasting has become increasingly popular in recent years, with many people turning to intermittent fasting to lose weight and improve their overall health. But while research suggests that fasting can combat oxidative stress, protect the heart, and even lead to a longer life, the thought of going for hours or days at a time without eating isn't appealing (or even feasible) for everyone.

Enter ProLon: the fasting-mimicking program being touted by fitness influencers and celebrities alike. The five-day ProLon plan claims to promote cellular renewal, support metabolic health, and even result in an average loss of five pounds. But what exactly is the ProLon diet? And more importantly, is it safe? We asked registered dietitians about the potential benefits of this trendy eating plan and for whom it's best suited.

What Is the ProLon Diet?

Prepackaged meals and timed eating plans are nothing new, but ProLon combines these concepts, serving up foods and drinks designed to mimic fasting. While traditional fasting means forgoing food completely for a period of time, fasting-mimicking diets allow the body to reap the benefits of fasting, while providing a specific amount of nutrients that help to minimize the side effects.

When you sign up for the ProLon diet, you'll receive five days' worth of plant-based foods and drinks in preportioned quantities, from vegetable-based soups to energy bars to teas. Along with your food, you'll also receive supplements providing high levels of minerals, vitamins, and essential fatty acids, which should be taken throughout those five days. All of the items that should be consumed in a day are individually boxed, so there's no confusion about what to eat and when.

The food in the ProLon system amounts to a low-carb, high-fat diet, providing between 700 and 1,100 calories per day. The composition of the macronutrients in this plan causes the body to undergo a process called gluconeogenesis. During gluconeogenesis, glycogen stores are depleted, and the body makes energy from noncarbohydrate sources. This plays a significant role in the positive health outcomes that are observed.

As the limited supplies would suggest, you only need to follow the ProLon diet for five days. After that, you can go back to your regular eating habits. It's recommended that you repeat the ProLon system every month for three months and every three to six months after that.

How Much Does the ProLon Diet Cost?

You can purchase a single ProLon box for $249 or subscribe to save on multiple deliveries.

What Are the Benefits of the ProLon Diet?

One impressive claim of the ProLon diet is that this method is backed by more than 20 years of extensive preclinical and clinical studies. A study on the ProLon diet, specifically, found that eating this way for five consecutive days per month, for three months in a row, resulted in a reduction in body weight, waist circumference, and body mass index (BMI). People who were at risk for conditions like high blood pressure and elevated triglycerides experienced the best outcomes, including improved fasting glucose, cholesterol levels, and markers of inflammation.

While the results of this study are impressive, they should be taken with a grain of salt for a few reasons. The sample size was small, with many people dropping out of the study due to scheduling conflicts or the inability to comply with the guidelines of the fasting-mimicking program. It's also important to note that the creator of the ProLon diet, Dr. Valter Longo, was one of the authors of the study, and the university where the study was conducted disclosed that it had the potential to receive royalty payments from ProLon's parent company.

Additional studies do exist to highlight the benefits of fasting-mimicking diets, but not necessarily the specific guidelines or proprietary foods that are the foundation for the ProLon program. For example, in one study that reported positive outcomes in people with breast cancer, the calorie range provided to participants was as low as 200 calories per day - much lower than that of the ProLon diet. Some of the studies that have reported benefits from fasting-mimicking diets also used animals as subjects, instead of humans.

Should You Try the ProLon Diet?

There are certainly potential benefits to following the ProLon program - or any fasting-mimicking diet, for that matter - but is it worth the investment, or should you skip this trend?

"ProLon is not a cleanse or weight-loss plan," Lauren Harris-Pincus, MS, RDN, author of The Protein-Packed Breakfast Club and The Everything Easy Pre-Diabetes Cookbook, told POPSUGAR. "While weight loss is a likely side effect of five days of significant calorie reduction, it is not the primary purpose, and a lot of it is the result of depleting your glycogen stores, which will rebound at least somewhat when you increase your calorie intake again."

However, ProLon can act as "a bit of a reset for the palate," Harris-Pincus explained, which she sees as a benefit. "It's amazing how delicious veggies taste during and after the process. It is also nice to not have to think about what to eat for five days, and the company offers support if you need it."

Sharon Puello, MA, RD, CDN, owner of Fresh Nutrition PLLC, said she's concerned about the diet's "hefty price tag," especially because it's unlikely to result in sustainable change. Puello explained that most people fare best when the foods they enjoy can be incorporated into a regular, healthy routine - "not when we're restricted to a few pricey foods we wouldn't ordinarily choose."

While Puello does believe in intermittent fasting and its benefits, she feels that fasting needs to be tailored to a person's individual lifestyle, nutritional needs, and goals, instead of the one-size-fits-all approach ProLon offers. However, "for the avid, generally healthy faster who wants to try a longer fast without the downsides of a water fast, this can be a decent option," Puello said. "The ingredients are simple and don't send up any red flags."

She added that the primary goals of a prolonged fast lean more toward reducing inflammation and balancing gut bacteria than losing weight. "If someone is considering this program for quick weight loss, it would not be something I would recommend," Puello told POPSUGAR.

Sarah Gold, MS, RDN, owner of Sarah Gold Nutrition, agreed. "Quick fixes like this don't actually teach an individual enough about healthy eating to lead to sustained positive changes," Gold said. And while this diet does include healthy fats, vegetables, and other good-for-you foods, it's missing entire food groups that are recommended as part of a healthy diet, including fruit, dairy, and fish.

Is the ProLon Diet Safe For Everyone?

Instagram influencers may tout the ProLon diet as a nearly universal solution, but researchers note that there are some things to consider when following this plan or any fasting-mimicking diet. "Fasting-mimicking diets or any type of prolonged fasting interventions lasting more than 12 hours, particularly those lasting several days, require supervision, preferably from a health care professional familiar with prolonged fasting," Dr. Longo and his colleagues wrote. They also noted that "additional studies are necessary to determine its safety for subjects who are 70 years and older."

Puello cautions anyone who has had bariatric surgery against the ProLon diet. Bariatric patients have higher protein and micronutrient needs than others, and so missing multiple days of adequate nutrition is not advisable, Puello explained. She added that anyone with a history of eating disorders should avoid this program.

Also on the list of those who should steer clear of fasting-mimicking diets, according to Harris-Pincus: pregnant people, those with certain medical conditions such as type 1 diabetes, or anyone with an occupation that requires them to be active and alert, such as first responders, heavy-machinery operators, pilots, or bus, truck, or train drivers. She also stressed the importance of discussing the ProLon diet with your doctor before starting the program, as certain prescription medications may be affected by a dramatic decrease in calories.

Bottom line? The ProLon diet may lead to positive health outcomes in some people - especially if the program is repeated every month for three months in a row, then every three to six months after that. But to say that this diet is safe and appropriate for everyone is a bit of an overstatement. Your best bet is to talk to your doctor before you fork over the $249 for your five-day box.