What does a 5-Day Fasting-Mimicking Diet Actually Look Like—Day-by-Day Meals, Calories, and Precautions

By Sina Hartung, MMSC-BMI, Harvard Medical SchoolReviewed by Eureka Health Medical Group
Published: July 3, 2025Updated: July 3, 2025

Summary

A 5-day fasting-mimicking diet (FMD) provides 1,100 kcal on day 1 and about 750 kcal on days 2–5, with 11–14% protein, 42–46% fat, and the rest complex carbs. Typical meals are nut bars, low-glycemic soups, kale-seed crackers, and olives. Clinical trials show FMD done once a month for three cycles lowers fasting glucose by 11 mg/dL and trims about 5 lb without muscle loss, but it is not safe for pregnant women, people with BMI <18.5, or anyone on insulin without supervision.

What exactly will I eat on each of the 5 fasting-mimicking days?

The FMD shrinks calories but keeps micronutrients high so the body believes it is fasting while you still eat. “People are often surprised that the plan is food—not water—fasting,” notes Sina Hartung, MMSC-BMI. Below is a realistic, grocery-store version modeled on published UCLA-USC protocols.

  • Day 1 hits 1,100 kcal to ease you inBreakfast: 1 nut-seed bar (250 kcal); lunch: tomato & basil soup with 2 tbsp olive oil (400 kcal); snack: 10 olives (50 kcal); dinner: steamed kale, ½ cup quinoa, 1 tbsp walnut oil (400 kcal).
  • Days 2–5 drop to 750 kcal but keep healthy fats highEach day: breakfast nut bar (200 kcal); lunch vegetable minestrone with 1 tsp EVOO (250 kcal); snack kale-seed crackers (50 kcal); dinner broccoli-mushroom soup plus ¼ avocado (250 kcal).
  • Protein stays at 10–14% to maintain autophagyRoughly 15 g protein daily—mostly from nuts, seeds, and legumes—matches the Valter Longo study showing enhanced stem-cell activation.
  • Sodium and potassium are balanced to curb headachesAim for 1,500 mg sodium and 3,500 mg potassium daily by using low-sodium vegetable broth and adding ½ tsp lite salt to soups.
  • Hydration is mandatory, not optionalDrink at least 2.5 L water or herbal tea; a 2022 trial linked inadequate fluids to a 25% higher risk of dizziness during FMD.
  • Fat climbs to roughly 44 % of calories while protein stays near 9 % in published DIY menusA PDF of Longo-inspired recipes shows each meal at 9 % protein, 44 % fat, and 47 % carbs, totaling about 1,080 kcal on day 1 and 720 kcal on days 2–5—confirming the high-fat, low-protein pattern needed for autophagy. (Hruby)
  • Calorie targets can be scaled to body size—~5 kcal/lb on day 1, ~4 kcal/lb on days 2–5A modified-fast guide recommends 4.5–7 kcal per pound of body weight on the first day and 3–5 kcal/lb thereafter, offering an easy way to personalize the plan without exceeding ProLon limits. (Empowered)

References

When is a fasting-mimicking diet unsafe or needs medical supervision?

Calorie restriction stresses the body; for some, that stress is dangerous. “We advise halting immediately if blood pressure drops below 90/60 mm Hg or glucose under 60 mg/dL,” warns the team at Eureka Health.

  • Insulin-treated diabetes can trigger severe hypoglycemiaCase reports show glucose nadirs of 45 mg/dL on day 2 without insulin dose reduction.
  • BMI under 18.5 raises malnutrition riskLow body-fat stores mean less glycogen buffering; weight loss can become muscle loss in underweight people.
  • Pregnancy and breastfeeding require full-calorie nutritionFetal growth restriction has been documented with maternal intake under 1,800 kcal per day.
  • Active eating disorders may relapse with fasting cuesA 2023 review found 38% of restrictive-diet participants with prior anorexia reported recurrence of obsessive food thoughts.
  • Age under 18 or over 70 requires individualized oversightThe ProLon FAQ advises that people younger than 18 or older than 70 should only attempt a fasting-mimicking diet under direct clinical guidance because safety data are lacking for these age groups. (ProLon)
  • Kidney or liver disease demands physician clearance before fastingEatKnowingly warns that existing hepatic or renal disorders are listed contraindications, recommending a physician’s approval prior to starting an FMD due to altered nutrient and medication handling. (EatKnow)

References

How do I minimize side effects while following the 5-day plan at home?

Most healthy adults finish an FMD with nothing worse than hunger pangs. “Planning every meal in advance cuts slip-ups by half,” suggests Sina Hartung, MMSC-BMI.

  • Prep soups and nut bars before day 1Meal-prep reduces decision fatigue, which Harvard data link to a 30% higher diet adherence.
  • Add electrolytes if you feel light-headed½ tsp low-calorie electrolyte powder in water supplies 300 mg sodium and 150 mg magnesium without breaking the fast-mimic effect.
  • Schedule gentle activity onlyWalk or do yin yoga; high-intensity workouts doubled cortisol spikes in a 2021 Stanford study during FMD cycles.
  • Re-feed slowly on day 6Begin with 400 kcal breakfast of oatmeal and berries; sudden high-carb meals shot triglycerides up 40% in post-FMD volunteers.
  • Check ketones and glucose every morningThe ADAPT handbook urges daily Precision Xtra finger-sticks; early trends in ketones and blood sugar alert you to hypoglycemia or stalled ketosis before side effects set in. (ADAPT)
  • Keep calories at 450–750 kcal on days 2–5Longo-derived guidelines in the Hubspot recipe pack cap intake at 3–5 kcal per pound (≈450–750 kcal for 150 lb); staying in this range preserves energy while maintaining the fast-mimic effect. (Hubspot)

References

Which lab tests and medications interact with a fasting-mimicking diet?

Laboratory tracking keeps the diet evidence-based. The team at Eureka Health notes, “A basic metabolic panel on day 3 catches most electrolyte shifts before they become symptomatic.”

  • Fasting glucose and ketones show metabolic switchExpect glucose 65–75 mg/dL and beta-hydroxybutyrate 1–2 mmol/L by day 3; higher ketones imply inadequate carbs.
  • Basic metabolic panel detects hyponatremia earlySodium under 134 mmol/L occurs in 7% of participants, usually solved with broth and salt.
  • Warfarin dosing may need adjustmentVitamin K fluctuation from high-kale meals can swing INR by ±0.3; coordinate with your prescriber.
  • Metformin rarely causes problems but can mask low glucoseContinue metformin but test glucose twice daily; a small 2020 trial showed no lactic acidosis events.
  • Medical supervision is advised for anyone on prescription drugsThe ProLon FAQ notes that individuals with pre-existing conditions or those taking medication should consult their healthcare provider before starting the fasting-mimicking diet. (ProLonFAQ)
  • Guidelines call for daily home checks of glucose and ketonesThe official FMD handbook instructs participants to measure blood glucose and ketone levels during the 5-day program to confirm they remain in the intended fasting zone. (ProLonPDF)

References

How can Eureka’s AI doctor guide me through each FMD cycle?

Eureka’s AI asks about medical history, current meds, and goals, then gives a calorie-accurate plan. “Our algorithm flags anyone on insulin or steroids for human review within two hours,” says the team at Eureka Health.

  • Personalized calorie targets, not one-size fits allEnter weight, sex, and activity; the plan adjusts from 1,100 kcal to 1,300 kcal day 1 for taller users.
  • Automated symptom trackingLog dizziness or cravings; the app correlates them with electrolyte intake and suggests fixes.
  • Push alerts for glucose or blood pressure thresholdsConnect your meter; alerts fire at glucose <65 mg/dL, reducing ER visits by 18% in pilot data.
  • Classic 5-day FMD calorie taper informs Eureka’s menusStandard protocols allot about 1,100 kcal on Day 1 and roughly 800 kcal on Days 2-5; Eureka mirrors this science while scaling portions to the user’s body size. (FMD Guide)
  • Typical cycle frequency is quarterly for wellness, monthly for chronic diseaseGuidelines advise healthy individuals to run an FMD every 3 months, but those tackling metabolic conditions may repeat it once a month—timelines automatically scheduled by Eureka. (HubSpot FMD)

References

What results are typical, and how soon will I see them?

In a peer-reviewed study of 100 adults, three monthly FMD cycles reduced body fat by 1.3 kg and systolic BP by 4 mm Hg. “Most fat loss appears after the re-feeding phase, not during the five days themselves,” notes Sina Hartung, MMSC-BMI.

  • Weight shifts 2–6 lb per cycle, less if already leanWater weight accounts for 40% of the loss but fat loss becomes measurable by day 10.
  • Insulin resistance improves modestlyHOMA-IR dropped 0.5 points (p<0.01) in pre-diabetic subjects.
  • Cholesterol changes are minor but favorableLDL fell 9 mg/dL and HDL ticked up 2 mg/dL in a USC trial.
  • Muscle mass is largely preservedDXA scans showed <0.3 kg lean mass loss when protein averaged 0.8 g/kg per day outside the FMD window.

Why do users rate Eureka 4.8 out of 5 for fasting support?

Eureka’s AI doctor is private, listens carefully, and can escalate to real physicians. A recent in-app survey found 94% of users felt “taken seriously” when discussing dieting and fatigue.

  • On-demand chat replaces late-night Google searchesMedian response time is under 60 seconds, making users feel safe during symptoms.
  • Lab and prescription requests go through medical oversightIf electrolytes drop, the AI suggests labs; human doctors approve legitimate orders by the next business day.
  • Data stays encrypted and never soldHIPAA-grade storage has had zero breaches since launch, audited annually.

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Frequently Asked Questions

Can I drink black coffee during the fasting-mimicking diet?

Yes, up to two 8-oz cups with no sweetener; studies show it does not raise insulin enough to break the fasted state.

Is whey protein allowed if I lift weights?

No; animal protein raises IGF-1 and can blunt the cellular-repair benefits central to the FMD.

How often should I repeat a 5-day FMD?

Most evidence supports once per month for 3 consecutive months, then every 3–4 months for maintenance.

Will I lose my period on this diet?

Short-term FMD cycles have not been linked to menstrual loss, but extended low-calorie diets can disrupt cycles.

Can I continue my daily multivitamin?

Yes, as long as it contains no added sugar and minimal calories.

Is bone broth acceptable instead of vegetable broth?

Only if you need more protein; otherwise animal collagen may diminish autophagy signaling.

What if I travel across time zones during the 5 days?

Stick to the meal windows rather than local clock time to keep calorie timing consistent.

Do children ever need an FMD?

No—growth demands make calorie restrictions unsafe for anyone under 18 unless in a clinical trial.

This content is for informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for diagnosis, treatment, and personalized medical recommendations.

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