A week ago, I embarked on the Fasting Mimicking Diet (FMD) and today I wanted to share my experiences with you.

Fasting Mimicking Diet

What is the Fasting Mimicking Diet (FMD)?

The FMD was designed by Professor Valter Longo, author of The Longevity Diet. Longo’s research primarily focusses on how to slow down the process of ageing.

Ageing is associated with a progressive functional decline of the immune system, often referred to as immunosenescence. This decline can lead to increased susceptibility to infection, autoimmune disease, chronic inflammation, and more.

After all who doesn’t want to age well?!

I for one have seen most of the people I know significantly deteriorate as they cross that bridge to 70 and the thought of it makes me shudder.

Why drag yourself to a hundred with disease, when you can be feeling good on your 100th birthday right?! I have no doubt that Captain Tom has inspired many of us during lockdown to realise that we can do exactly this.

The good news is that periodic fasting appears to be a really good start to achieving this goal of ageing well. So let’s take a look at the FMD in a little more detail.

FMD objectives and goals

Is to provide:

  1. Sufficient calories to be safe
  2. A variety of components that people can enjoy
  3. 100% plant-based diet
  4. An equally effective method of fasting as water fasting, but with food

So how does the FMD work?

The beauty of this diet is that you get to reap the benefits of fasting, but you still get to eat. This approach is definitely easier than fasting with no food. In fact, fasting with no food can cause a breakdown in body tissue, such as muscle, which is not something you really want to lose. The FMD preserves muscle, whilst getting rid of stored fat and cellular waste.

What are the benefits of FMD?

  • Promote and activate stem-cell regeneration in the immune system, nervous system and pancreas. Stem cells are the body’s raw material from which other cells with specialised functions are generated. It has become a hot topic of late as we are learning that you can actually guide stem cells into becoming specific cells that can be used to regenerate and repair diseased or damaged tissue.
  • Fasting destroys damaged cells and damaged components inside the cells. Additionally, the inside of cells are partially rebuilt, a process known as autophagy. I like to think of autophagy as a computer reboot, thereby rejuvenating your body on a cellular level.
  • Fasting can switch cells on to protect against ageing.
  • Shift the body into a visceral (abdomen) fat-burning mode, which continues even after returning to a normal diet. This, according to Longo, is possibly due to epigenetic changes that lead to the modification of DNA.
  • Weight loss, and I can vouch for this. I lost 2.5kg in 5 days (ding-dong!)
  • Improve fasting glucose levels
  • Decrease blood pressure in people with high blood pressure, but doesn’t seem to reduce it in those with low blood pressure
  • Improve cholesterol
  • Reduce C-Reactive protein, a key marker for inflammation
  • A reduction in triglycerides, which is your stored form of fat
  • Reduce proinflammatory cytokines and thus inflammation

Overall, it is said to reduce risk factors for diabetes, cancer, cardiovascular disease after just three cycles of FMD done over three consecutive months. What’s not to like?!

So how does this compare to other forms of fasting?

There are many different approaches to fasting, such as water fasting, religious fasting, periodic fasting, time restrictive feeding and intermittent fasting. At the time of writing this, ‘Prolon is the first and only Periodic Fasting Mimicking Diet and is scientifically developed, and clinically proven, to induce the protectionist and rejuvenation mode. No other meal programme is capable of inducing these benefits.’

Without going into the specifics of each diet, the table below provides a good cross comparison on the key areas.

Fasting Mimicking Diet

How often should you be doing the FMD?

The FMD guidelines suggest that you should do this once per month for three consecutive months. However, variations include once a season, twice a year, or even once a year. In some challenging conditions, like autoimmunity, the suggestion is once a month for a year.

Why did I embark on the FMD?

Apart from gaining a deeper understanding of the plan before recommending it to my clients, I wanted to review the impact on thyroid, adrenal and immune health. I have a long history of adrenal insufficiency and Hashimoto’s disease (autoimmune thyroiditis), which can make fasting complicated for some individuals. Fortunately for me, I have no problems with intermittent fasting or time restricted feeding, yet I do find that low calorie ‘diets’ negatively impact my blood sugar, adrenal and thyroid function.

From my personal research into the FMD, I felt confident, that the product was well rounded, with no specific food allergens that would be problematic to me and also with no risk of nutrient deficiencies. One of the key criteria for me was that the products didn’t contain any soy, which can be very problematic for people with thyroid disease like myself. I was also aware of some success stories in people with Hashimoto’s disease and wanted to find out for myself.

What was my experience with the FMD?

Some of you might have been following my journey with Prolon on Instagram and Facebook. If you haven’t then you can watch the short videos I did each day to showcase the daily meal plans. You can find this under ‘Fasting’ stories on Instagram.

Preparation week

It is recommended that you reduce your protein consumption to at least 0.8 grams of protein per body weight in kilograms for at least a week before you start the FMD. The protein should predominantly be obtained from vegetables and fish. To complement this, you need to take an omega-3 supplement at least twice a day during the preparatory week.

Day 1

The food consisted of 1,100 calories broken down as follow:

  • 500 calories from complex carbohydrates (vegetables, such as broccoli, tomatoes, carrots, pumpkin, mushrooms, etc.)
  • 500 calories from healthy fats (nuts, olive oil)
  • 1 multivitamin and mineral supplement
  • 1 omega 3 & 6 supplement
  • Sugarless tea (up to 3-4 cups a day)
  • 25g plant-based protein, mainly from nuts
  • Unlimited water

I actually found the first day pretty easy. I didn’t feel that hungry and actually really enjoyed the food, apart from the minestrone soup (which fortunately became a favourite by day five).

My energy levels were really good, I had no specific ‘symptoms’ that prompted me to feel concerned.  I am specifically referring to pain around my thyroid, low blood sugar, noticing changes in my adrenals, bowel movements and sleep.

Day 2 -5

  • Total calorie intake was 800 calories a day (vegetables, such as broccoli, tomatoes, carrots, pumpkin, mushrooms, etc.)
  • 400 calories from healthy fats (nuts, olive oil)
  • 1 multivitamin and mineral supplement
  • 1 omega 3 & 6 supplement
  • Sugarless tea (up to 3-4 cups a day)
  • Unlimited water

Day 2

My energy levels were really good throughout the day and despite feeling a bit hungrier, I managed well. Day two was the only day where I noticed some symptoms that signalled inflammation, but it didn’t last. My thyroid was great, my mood was amazing, my mental clarity was definitely improving and my bowel movements were still good.

Day 3

I felt really hungry at the start of day 3. My energy levels were great, cognitive function was definitely much sharper, my thyroid felt good, I had no issues with blood sugar imbalances at any point throughout the day and my sleep was good.

Day 4

I noticed an increase in ketones, which led to not really feeling hungry. Sadly, this didn’t last beyond the first meal. In fact, I found that I was really hungry for the rest of the day once I had my first meal. Having said this, the hunger doesn’t really last that long and soon subsides, so it really isn’t that bad! I found that my energy levels continued to increase, so did my mental clarity and mood. I had no issues with my thyroid, adrenals, blood sugar (this was so stable) and bowel movements and sleep.

Day 5

Despite feeling a bit hungry between meals, my energy levels and mental clarity was amazing. Interestingly, my recovery from exercise was good (something that can be challenging for me sometimes). Could this have highlighted a reduction in inflammation? Time will tell!

Prolon Diet

The benefits for me

  • Significant increase in energy
  • Improvement in mental clarity
  • Amazing blood sugar control (I never experienced a single wobble)
  • Fantastic recovery from exercise
  • Weight loss
  • Good sleep overall
  • Thyroid felt great
  • Good mood

Throughout the 5 days I continued to follow time restricted-feeding, fasting for approximately 16 hours (some days I did go a little longer), and then eating in an 8-hour window. This worked really well for me during the FMD. I am not advocating that this is the way to use the FMD, but it was a good way for me to manage the programme.

Is the FMD right for you?

The FMD is NOT suitable for:

  • Children under the age of 18
  • Pregnant women
  • Lactating women
  • People with nut allergies
  • Anyone with serious medical conditions

If you have any medical conditions or take prescription medication, then it is best to do it under the guidance of a practitioner.

The people who are most likely to benefit are those who with:

  • Insulin resistance and metabolic syndrome
  • High blood sugar
  • Undergoing chemotherapy
  • High triglycerides
  • Excess/stubborn abdominal fat
  • Weight loss resistance
  • Low energy
  • Difficulty concentrating
  • Poor memory
  • High Blood pressure
  • Risk for cardiovascular disease /cardiovascular disease
  • Chronic inflammation
  • Autoimmune disease

You can actually complete a quick questionnaire to find out if the FMD is right for you.

Autoimmune Disease and the FMD

At present there is not a great deal of research on the effectivity of the FMD for autoimmune disease. A few small scale studies on patients with Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA) in both humans and mice show a potential promise, but more research is needed to fully evaluate the impact of the FMD on autoimmune disease.

In one study, 20 patients with MS reported significant improvements in physical and mental health after just a single cycle of FMD.

Thyroid and the FMD

Whilst I am not aware of any specific research on the impact on thyroid disease, I believe this is something that is happening in the side wings as I write this.

Fasting most certainly doesn’t work for everyone, and this can be especially true for people with hypothyroidism.


Stress very often plays a significant role in the onset of hypothyroidism and can change the way the body converts and utilise thyroid hormone. When the body is under stress, it can present as increased levels of reverse T3, which is a biologically inactive metabolite of thyroxine (T4) formed by deiodinase enzymes. The activity of these deiodinase enzymes are regulated by both nutritional and physiological conditions. Higher levels of reverse T3 are generally associated with periods of prolonged stress, starvation or extreme carbohydrate restriction, chronic heart failure. When someone has higher levels of reverse T3 (which fortunately I don’t have), fasting might exacerbate symptoms and further impact thyroid function.

My advice therefore is to work with a practitioner who can tell you whether the FMD is suitable for your thyroid health.

One other key consideration of the FMD for thyroid disease is the role of stem cells.

Stem cells and your thyroid

There has been a few studies, albeit on rats and mice, that has shown promising results in improving thyroid function with the use of stem cell therapy.

One study showed that mice without thyroid glands, were able to produce normal amounts of thyroid hormone eight weeks after stem cell transplant. These stem cells were used to grow thyroid cells without any sign of tumour formation.

Another study with rats showed that stem cell transplants reduced both thyroid antibodies and proinflammatory cells (Th17), whilst increasing cells that help maintain tolerance to self (T-reg cells).

One of the key benefits of the FMD is an increase in stem cells. We know that starvation forces the bone marrow to create new stem cells and replace faulty immune cells with healthy ones. This can therefore be another promising aspect of the FMD for thyroid disease, but we definitely need more research before we get too excited about it.

I hope you have found this helpful. Please leave any questions or comments below.

Nutritional Therapist Cheshire, Health, Nutritionist Cheshire, Functional Medicine Cheshire, Rootcause Solution


  1. https://prolonfmd.com/wp-content/uploads/2016/10/cell-press-may-2016.pdf
  2. https://prolonfmd.com/wp-content/uploads/2016/10/jama-august-2016.pdf
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5862044/
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3856718/
  5. https://www.tandfonline.com/doi/abs/10.1080/08916934.2019.1697689
  6. https://www.frontiersin.org/articles/10.3389/fendo.2014.00055/full
  7. https://www.empoweryourhealth.org/magazine/vol10_issue1/the_promise_of_stem_cell_regenerative_therapy_for_restoring_thyroid_function
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2709484/
  9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6816332/