Fasting Mimicking Diets?

Fasting is one of those wellness topics that seems to divide opinion faster than oat milk versus dairy. Since beginning my nutrition studies, it is something that comes up constantly in conversations with friends, practitioners, clients and wellness enthusiasts alike. Everyone seems to have a view.

Some people swear by it. Others hear the word “fasting” and immediately reach for a croissant in self defence.

For years, I sat somewhere in the middle. Curious, sceptical and slightly hungry. I had attempted to fast before. In my twenties I dabbled and tried a water fast, lasting just over 24 hours before developing a headache, low energy and an intense emotional attachment to pasta. It did not go well.

Because the reality is, I genuinely love food. The smell of it, cooking for people, sharing meals with family and friends, the texture, the taste and even the simple act of chewing. Honestly, I sometimes think chewing itself is part of my emotional regulation strategy. But despite my love affair with food, the research around fasting and longevity is fascinating. Particularly when it comes to inflammation, metabolic health and a process called autophagy.

What is autophagy?

Autophagy is the body’s natural clean up and recycling process. During this process, damaged or dysfunctional cellular material is broken down and recycled so the body can repair and renew itself more efficiently.

Think of it as a spring clean for your cells.

Research suggests autophagy may play an important role in healthy ageing, inflammation, metabolic health and disease prevention, particularly during periods of fasting or mild stress¹. As someone interested in preventative health and healthy ageing, this obviously caught my attention. So recently, I decided to try a five day fasting mimicking diet, also known as an FMD.

What is a fasting mimicking diet?

Unlike complete fasting, a fasting mimicking diet involves eating carefully designed low calorie, low protein foods that help shift the body into a fasting like state while still providing nutrients. The aim is to encourage fat burning, cellular repair and metabolic reset without fully depriving the body of food.

Appreciating the sleek packaging

My reasons for trying it?

Well it was partly curiosity, but I also felt like I needed a biological reset. Easter chocolate had lingered slightly too long, my caffeine intake had started to creep up and my rheumatoid arthritis inflammation had been more noticeable recently. Feeling puffy, sluggish and slightly out of sync with myself.

What does the research suggest?

Whilst associated with weight loss and deceased fat mass, rather than protein muscle loss (unlike GLP-1 drugs)²,  I was also intrigued by emerging research, involving randomised control trails (RCT - gold standard testing),  showing improvements in biological ageing markers, with 3 cycles of FMD (15 days over 3 months) being associated with a decrease in biological age of 2.5 years in median biological age, independent of weight loss; with reduced insulin resistance, lower liver fat and reduced systemic inflammation (C-reactive protein/CRP)³.  Another recent RCT involving Stanford University investigating individuals with mild to moderate Crohn’s Disease (CD) highlighted that following an 5-day FMD once a month, for 3 months, achieved clinical remission in 64.6% of individuals and there was a statistically significant decrease in faecal calprotectin (a marker of inflammation with in the gut), and other CD related immune markers, compared to the non-FMD control group⁴.

With suggestions within the health arena of discussions with leading medical authorities in the US, Middle East and UK looking to potentially integrate this protocol into medical guidance, with a particular focus on Type 2 Diabetes, this felt like it deserved my attention.

And honestly, I simply wanted to experience it for myself.

Day 5 and smiling

Five days without normal food: an honest review

Day 1

Surprisingly manageable. I even survived sitting with my family while they enjoyed a full Sunday roast as I quietly sipped soup and attempted to radiate inner wellness.

Day 2

This was harder. I had an all-day event to attend and definitely noticed brain fog by the evening. Oddly though, being busy actually helped because it distracted me from constantly thinking about food and how I felt. I took the soup (already made up) in a thermos flask and it was a great conversation starter during the event.

Day 3

Brutal. I felt cold. I missed vegetables. I missed crunchy textures and chewing in general. I also became disproportionately upset by the absence of olives in the meal pack. My husband kindly informed me that my stomach had spent the night making dramatic growling noises, which apparently kept him (and the cat) awake.

Day 4

Something shifted. I woke up feeling mentally clearer, lighter and much less focused on food. Whilst I still felt cold, my energy felt steadier and I seemed more settled into my daily routine.

Day 5

By the final day, my joints felt noticeably less swollen, my skin looked brighter and someone commented that my eyes looked “sparkly.” Although admittedly this may simply have been relief that normal meals were finally in sight. I felt calmer too.

Did it work?

Yes, I lost weight. Around 2.5kg. But genuinely, that was not my main goal.

What interested me more was how differently I felt afterwards. My cravings had changed quickly. I naturally wanted healthier foods, although I accept that I do typically tend to eat healthy, nutritious food. My desire for coffee dropped dramatically, I just did not need or think about it, and my body simply felt calmer overall. I've not felt the need for my typical pre-fast mid-afternoon nut snack since I finished too.

Maybe it was phycological, but I felt cleaner just like after a spring clean.  I was advised that the effects would taper down over the days following the fast, rather than just dropping off like the edge of a cliff, and I felt the ongoing effects until the start of the new week.

As someone living with rheumatoid arthritis, I was particularly interested in how it affected inflammation and joint swelling. With a recent flare due to hormones and medication issues (more about that another time), I was realistic that symptoms were unlikely to disappear. Personally, I noticed a clear improvement, with less morning stiffness and pain in my hands and hips. I appreciate this is entirely anecdotal and everyone’s experience will be different but for me I saw this as a sign that something internally had shifted.

Others in my support group were more experienced, with some individuals being on their 12^th fast and having experienced first hand the health benefits and improved blood test results over the years. So yes it is interesting.    

Would I do it again?

Yes. Although ideally not during an especially stressful, demanding work week, during school holidays and definitely not when I know there are family celebrations or social events planned that might tempt me.

I liked the idea that everything was provided for me in a box, containing smaller numbered boxes for each day and simple to understand guidance and instructions.  There were soups, crackers, green olives, snack bars, herbal teas, occasional supplements and a glycogen drink to mix with water (depending on weight) – noting that the menus can vary (I had meal plan variety 3). The food was fine – by day 5 I was ready to move on, but the items were surprisingly tasty.

Inside the box - my 5 days of eating planned out for me

The research around fasting mimicking diets is growing rapidly, particularly in relation to metabolic health, inflammation and healthy ageing. However, it is important to say that fasting is not suitable for everyone, especially those with a history of disordered eating, certain medical conditions or specific nutritional needs.

This is why professional guidance and suitability checks matter.

Overall though, it was one of the most interesting health experiences I have tried in a long time. Not because it felt extreme or restrictive, but because it made me think differently about food, my habits, inflammation and the body’s remarkable ability to adapt and repair.

And now, if you will excuse me, after five days of powdered soup and olive scarcity trauma, I am off to fully appreciate the simple joy of chewing a proper meal in the sunshine. Assuming British weather allows it.

Details:  

I used the Prolon 5-day FMD as an introduction and was a guest within a practitioner supervised group. If you have any questions regarding Prolon, or are interested in trying it for yourself then please reach out and contact me (via contact tab on the website).

References:

1.      He, J. and Qi, T. (2026) “Autophagy: mechanisms, roles in human diseases, and therapeutic perspectives,” Frontiers in Cell and Developmental Biology, 14. Available at: https://doi.org/10.3389/fcell.2026.1776289.

2.      Wei, M. et al. (2017) “Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease,” Science Translational Medicine, 9(377). Available at: https://doi.org/10.1126/scitranslmed.aai8700.

3.      Brandhorst, S. et al. (2024) “Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk,” Nature Communications, 15(1). Available at: https://doi.org/10.1038/s41467-024-45260-9.

4.      Kulkarni, C., Fardeen, T., Gubatan, J. et al. A fasting-mimicking diet in patients with mild-to-moderate Crohn’s disease: a randomized controlled trial. Nat Med 32, 1023–1033 (2026). https://doi.org/10.1038/s41591-025-04173-w