Here's What To Know About the ProLon Diet

This "fasting with food" plan is gluten-free and uses mostly plant-based ingredients. Here's what it's all about and what to know if you're thinking about trying it.

As registered dietitians may be able to tell you, fasting seems to be competing with the popular keto diet when it comes to shedding pounds. Of the numerous ways to fast, the ProLon method might be compelling enough for you to try it, and to recruit someone to try it along with you.

The five-day meal program called ProLon is actually a fasting-mimicking diet. In other words, the plan shifts your body into fasting mode and allows your cells to reap the benefits of fasting, while still allowing you to eat a limited amount of food. Here's a primer on what the diet is, its benefits, cost, potential downsides, and more.

What the ProLon Plan Is

What is intriguing about ProLon is that it's based on years of research from one of the most well-known longevity experts in the country, and the studies on its outcomes are impressive. It's also in line with some eating philosophies: ProLon is 100% plant-based, gluten-free, and non-GMO, with no artificial additives.

ProLon was created by Valter Longo, PhD, director of the Longevity Institute at the University of Southern California in Los Angeles. The company's research partners include well-respected organizations, such as the Mayo Clinic and the Texas-based MD Anderson Cancer Center.

After over a decade of studies in both animals and humans, Dr. Longo developed a patented eating plan that activates the body's fasting mode, but provides enough food to simultaneously nourish cells and support metabolic balance. This "fasting with food" approach also reduces some of the risks tied to extreme fasting, which may include very low blood sugar and/or blood pressure, reduced immune function, fatigue, and low productivity.

The specific combination of limited plant protein, calorie restriction, good fats, and low-glycemic index carbohydrates in ProLon regulates the body's nutrient-sensing pathways, meaning cells believe they're not being fed. At the same time, the diet triggers anti-aging pathways responsible for cellular repair and regeneration.

ProLon vs. Other Types of Fasting

ProLon is considered to be a type of periodic fasting, as opposed to time-restricted feeding (for example, narrowing your eating window to 4–8 hours a day) and intermittent fasting (such as eating just 500–600 calories two nonconsecutive days a week).

The studies on ProLon's outcomes are pretty remarkable, particularly given that the plan is just five days in length. One study published in Science Translational Medicine in 2019 compared a control group with no diet intervention to a group that followed ProLon five days a month for three months. The ProLon group lost body weight and belly fat while maintaining lean muscle mass. They also experienced reductions in blood pressure, cholesterol, and CRP, an inflammatory marker, in addition to an increase in stem cell production, as well as reduced levels of insulin-like growth factor (IGF-1), a hormone linked to cancer risk when elevated.

According to scientists, these health-protective results appear to be limited to the precise makeup of the ProLon plan and are not seen in other periodic fasts, such as a juice cleanse, or even a longer-term keto diet. The latter has actually been shown to trigger unhealthy outcomes, including constipation, vitamin and mineral deficiencies, and increased cholesterol.

In addition, the majority of the ProLon results were sustained, even after participants resumed their normal diets. For example, 115 days after the protocol, 60% of the weight lost and reductions in waist measurements were maintained.

Other research-based ProLon outcomes include reductions in glucose, insulin, triglycerides, and blood pressure, as well as improved stress resistance and cognitive performance.

What's Included in the ProLon Plan

ProLon's packaging is stellar. The sleek, modern, glossy white kit is reminiscent of unboxing a new MacBook or iPhone. Inside sit five smaller boxes, marked Day 1, Day 2, etc. Each contains all of the food allowed for that specific day, which is made up of 73 carefully chosen plant ingredients. The protocol does not allow you to change the order of the days or swap foods from one day's allotment to another. You can, however, decide how you'd like to arrange your daily meals, although a suggested menu card is provided.

Foods provided include dried soup blends (which require adding hot water), proprietary nut and cocoa-based bars, pouches of olives and kale flax crackers, and a few supplements, including algal oil for plant-based omega-3 fatty acids, and a multivitamin/mineral. The kit also contains herbal teas and a large water bottle used to sip a flavored glycerol-based drink, which is used days two through five to help maintain fullness.

A very straightforward instruction sheet is provided, which lays out how to follow the plan. An FAQ on the brand's website answers additional questions about things like coffee (one cup of black per day is allowed), adding lemon to water (one wedge per day is OK), sprinkling herbs into the soup (one teaspoon per day is permitted), and drinking sparkling water (fine, as long as it's all natural with no artificial sweeteners).

What Following ProLon Is Like

For some people, getting through the five days isn't easy. Particularly, people who are taller, have a muscular build, or work a physically demanding job may find following this diet challenging. Here's an example of what you may expected day to day on this diet.

Day one may feel like a bit of a breeze. That day provides the most food, which is all tasty and enjoyable. If you're already on a plant-based diet, the switch won't be that significant. And having all of your food for the day pre-planned frees you from making meal decisions and makes the diet easy to follow.

On the first night, you may be thinking, "OK, I can do this, it's only five days." But you may start missing fresh food on day two. Especially if you typically eat five cups of non-starchy veggies each day, plus two cups of fruit, in addition to fresh avocado and plant proteins like lentils and beans.

You may also find yourself growing weary of eating only packaged foods and feeling the hunger. However, you may be encouraged by a reduction in bloating and feeling lighter—reasons to stick it out.

By day three some people get hangry, while others may experience a euphoric-like high and mental clarity that can accompany fasting.

Day four can seem slightly easier, because you're over the hump. But the dry packaged food can become pretty unappealing by this point, and you may want to do things to make it more palatable. For example, you can soak the kale flax crackers in the soup to mix up the texture, savor every morsel of the bars, and drink the juice from the olive pouches. You may also find yourself not sleeping well and becoming distracted by thoughts of foods you can't wait to eat again.

By day five you may be ready for ProLon to be over. Some people experience fatigue on this day—but it's the last day, so it's manageable. Once you've made it through day five, the ProLon protocol encourages slowly transitioning back to solid food on day six.

ProLon Results

Results of the ProLon diet are mixed. Some people see the desired results, while others don't. This makes sense, as the research shows that those with the highest BMIs experienced the greatest weight loss results.

Some of the results, like the weight loss and smaller waist size, can simply be due to water weight and less bloating. After resuming a normal diet, you may maintain some of the waistline difference and weight loss. ProLon provides 1,100 calories on day one, and 750 calories days two through five, which can be very extreme for people who are muscular and have physically demanding lifestyles.

Everyone's experience will be a bit different. In the three-month study mentioned earlier, the average weight loss was 5.1 pounds, primarily from abdominal fat. And in case you're wondering, no, you should not extend the program past five days or complete more than one cycle per month. After three months, the company encourages repeating the diet "from time to time" when looking for rejuvenation.

ProLon Pros, Cons, and the Bottom Line

ProLon isn't cheap. One kit costs $249, so about $50 per day, although this does include a consultation with a registered dietitian or nurse practitioner. Strenuous exercise should not be preformed while following the plan, and activities like driving long distances, prolonged sun exposure, or being in a hot tub or sauna should be avoided. Researchers say that exercise may actually negatively impact the outcome of the fast, so if anything, only slow walking, stretching, and light yoga are advised. The plan also encourages paying attention to how you feel, as side effects like lightheadedness can occur.

You should not try ProLon if you're pregnant or nursing, underweight, or have a history of an eating disorder. And anyone with a chronic medical condition, including type 2 diabetes, or heart or liver disease, should get a doctor's approval prior to trying ProLon.

As for allergies, all of the ingredients in ProLon food are visible online, so if you have any food allergies or intolerances you should check to see if you can follow the plan. ProLon states that the diet is not appropriate for those with allergies to nuts or sesame, for example.

Bottom line: Some people are encouraged to try the diet again, while others feel the opposite. The research seems to suggest, however, that the long-term results are unique to the ProLon protocol.

Here are a few caveats apart from those above for anyone curious about ProLon. First, if any kind of strict eating plan tends to trigger you emotionally, skip ProLon. In other words, if a previous cleanse led to a pizza binge by day two, ProLon is not the plan for you. If you're a premenopausal person, don't schedule ProLon just before your period, when cravings can be more intense. And if your work is physically demanding, it's safest to wait to follow ProLon when you have five consecutive days off.

Finally, don't go it alone. If you don't have a significant other, friend, or family member to do it with you, follow ProLon under the supervision of a registered dietitian who can coach you through the five days. The support and personalized guidance can invaluable. ProLon can be an investment in your health. Just be sure to examine if it's the right one for you before you hit the "add to cart" button.

Cynthia Sass, MPH, RD, is Health's contributing nutrition editor, a New York Times best-selling author, and a private practice performance nutritionist who has consulted for five professional sports teams.

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  1. Wei M, Brandhorst S, Shelehchi M, et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular diseaseSci Transl Med. 2017;9(377):eaai8700. doi: 10.1126/scitranslmed.aai8700

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