A five-day nutrient cycle that triggers fasting-like shifts linked to healthier ageing
Imagine eating nut bars and vegetable soup for five days, then going back to normal life… and lab tests say you’ve become 2.5 years “younger” biologically.
🥣 That’s what new research on the fasting-mimicking diet (FMD) suggests: a tightly designed 5-day, plant-based, low-calorie protocol that makes your body act as if you’re water fasting, even though you’re still eating.
Key Takeaways
- Fasting-mimicking diet (FMD) is a 5-day, low-calorie, low-protein, plant-based protocol done about once a month
- In two clinical trials, 3 cycles of FMD lowered biological age by ~2.5 years on average, and improved insulin resistance, liver fat, and immune ageing markers.
- Another trial found 4 monthly FMD cycles improved blood vessel function and cardiometabolic risk vs a continuous Mediterranean diet in overweight hypertensive adults.
- The method works by lowering glucose, insulin and IGF-1, raising ketones, and pushing cells from growth mode into repair mode
- It’s promising but not for everyone: people with diabetes on meds, underweight, pregnant, or with eating disorders need medical supervision
What Exactly Is the Fasting-Mimicking Diet?
🤔 FMD is often called the “fake fasting” diet because it keeps you fed while making your body behave like you’re on a water fast.
For 5 days, total calories drop to roughly 40–50% of your usual intake. Protein and carbohydrates are kept low, while unsaturated fats (like olives, nuts, seeds, olive oil) make up most of the energy. The foods are mostly plant-based soups, nut bars, teas, veggie snacks and specific supplements.
After those 5 days, people go back to a normal or Mediterranean-style diet for about 25 days. That cycling is important: the goal is short, intense metabolic stress, then plenty of recovery time.
For many, this feels more realistic than “always eat less” or “never eat after 6 pm.”
What The New Research Actually Tested
The big 2024 Nature Communications paper didn’t just look at weight loss. It zoomed in on markers of ageing and disease risk.
Across two clinical trials (including adults 18–70):
- Participants did 3 to 4 monthly FMD cycles, each lasting 5 days
- The rest of the month, they ate normally (often Mediterranean-ish, not strictly controlled)
- Researchers measured:
- Fasting glucose, insulin, HOMA-IR (insulin resistance)
- HbA1c (long-term blood sugar control)
- Liver fat and abdominal fat with MRI
- Immune markers, including lymphoid-to-myeloid ratio
- Biological age, using a validated algorithm based on blood markers
🧪 The headline result: after just three 5-day cycles, participants’ median biological age dropped by about 2.5 years, while controls didn’t see that shift. Insulin resistance improved, liver fat dropped, and immune profiles looked more “youthful.”
Separately, a 2023 randomized trial in overweight, hypertensive adults compared 4 cycles of FMD with a continuous Mediterranean diet over 4 months. Both groups improved, but the FMD group showed stronger gains in blood vessel function and cardiometabolic risk markers, even though they only restricted for 5 days a month.
How “Fake Fasting” Changes Your Biology
The power of FMD is not magic food. It’s messaging. You’re sending specific signals to nutrient-sensing pathways that control ageing and repair.
1. Glucose & Insulin Drop, Ketones Rise
During the 5 days:
- Calories fall by about half
- Carbs are low
- The body taps into stored energy and starts producing more ketones
Glucose and insulin come down, and insulin resistance markers like HOMA-IR improve. That’s why FMD is being studied for pre-diabetes and metabolic syndrome, not just longevity fans.
2. Growth Pathways Quiet Down
Protein is kept very low to dial down IGF-1 and mTOR, which are growth-signaling pathways. These are great when you’re building muscle, but chronically high IGF-1 is linked to faster ageing and higher cancer risk in animal work and some human data.
By suppressing these pathways for a few days, FMD appears to shift the body from “grow” mode to “repair” mode.
3. Cellular Cleanup & Immune Renewal
🧬 In both animal studies and human biomarkers, FMD cycles:
- Support autophagy, the “cell-cleaning” process that clears damaged components
- Encourage regeneration of immune cells
- Improve the lymphoid-to-myeloid ratio, a blood marker associated with a more youthful immune system
That immune shift is part of why researchers talk about immune system rejuvenation, not just better blood sugar.
How FMD Compares To Other Popular Diets
This is where FMD earns its “biohacking protocol” reputation.
Versus standard intermittent fasting (16:8, OMAD)
- IF focuses on when you eat
- FMD focuses on what and how much you eat for 5 days
- FMD has more controlled protein and macro ratios, which appear crucial for lowering IGF-1 and biological age
Versus ketogenic diets
- Keto can raise ketones but often includes moderate to high protein, which keeps IGF-1 signalling up
- FMD is brief, low-protein, higher-fat and intentionally designed to trigger “fasted state” biology despite food intake
Versus chronic calorie restriction
- CR asks you to eat less every day, for months or years
- FMD compresses restriction into short, intense cycles
- Early data suggests these periodic hits of metabolic stress may deliver many of the same benefits, with better real-world adherence
Five hard days per month is easier than being “good” forever.
Who Might Benefit Most (And Who Should Avoid It)
🧭 Based on the current evidence, FMD could be particularly interesting for:
- People with pre-diabetes, insulin resistance or fatty liver, under medical supervision
- Longevity seekers focused on biological age and immune ageing
- Busy professionals or athletes who want structured “repair weeks” instead of constant restriction
But there are clear red flags. FMD is not recommended for:
- Children and teenagers
- Pregnant or breastfeeding people
- Anyone underweight, or with a history of eating disorders
- People with serious chronic illness (especially kidney disease, advanced liver disease, or frailty)
- People with diabetes on glucose-lowering medication unless closely supervised, because glucose can drop significantly.
If any of that sounds like you, this protocol belongs in a doctor’s office conversation, not a solo experiment.
How A Research-Inspired FMD Cycle Looks
This is not medical advice, and the exact commercial formulas used in trials are proprietary, but here’s roughly what participants did:
Day 1
- About 1,100 kcal
- Low protein, low carb, rich in unsaturated fats
- Plant-based foods like nut bar, vegetable soup, olives, herbal teas, plus a micronutrient supplement
Days 2–5
- About 750 kcal per day
- Very low protein (around or below 10% of calories)
- Low carbs
- Fats mostly from nuts, seeds, olives, olive oil
Days 6–30
- Back to normal or Mediterranean-style diet
- Emphasis on vegetables, legumes, whole grains, fish, olive oil, minimal ultra-processed food
📌 One important detail: researchers saw most of the benefits after three consecutive monthly cycles. So this is not a “one weekend and done” trick.
If you ever try an FMD-style approach with a clinician, expect:
- Lower energy on fasting days
- Possible headaches, irritability, sleep changes
- The need to adjust training volume (not the week to crush personal records)
FAQ
Does FMD really slow ageing, or just tweak lab numbers?
Right now, we have surrogate markers: biological age algorithms, insulin resistance, liver fat, and immune ratios. Those are strongly linked to disease risk, but we don’t yet have 10-year follow-up showing fewer heart attacks or longer life. It’s very promising, not proven immortality.
Can you do FMD all the time to get more benefit?
Probably not a good idea. Chronic low calories and low protein risk muscle loss, hormonal problems and frailty. The whole point of FMD is brief, periodic stress, then full recovery with a healthy diet.
Can you just copy this at home with salads and nuts?
You could approximate the pattern, but the trials used carefully designed meal kits with validated macros. If you improvise, you might miss the low-protein and low-calorie targets, or go too hard and feel awful. Anyone with health issues should work with a professional.
Sources
- Brandhorst S et al. Fasting-mimicking diet causes hepatic and blood markers changes indicating reduced biological age and disease risk. Nature Communications 2024. https://www.nature.com/articles/s41467-024-45260-9
- Mishra A et al. Fasting mimicking diet cycles versus a Mediterranean diet and cardiometabolic risk in overweight and obese hypertensive subjects: a randomized clinical trial. npj Metabolic Health and Disease 2023. https://www.nature.com/articles/s44324-023-00002-1
- National Institute on Aging. Can fasting reduce disease risk and slow aging in people? 2024. https://www.nia.nih.gov/news/can-fasting-reduce-disease-risk-and-slow-aging-people
