Can fasting improve your immunity?

Can fasting improve your immunity?

We’ve had countless inquiries from our patients and community about whether or not fasting is safe or beneficial for increasing immune function at this critical time. We know that a lot of you utilize intermittent fasting and time restricted eating which you can continue if it feels manageable throughout this time.  However, most of your interest has been specifically focused on the fasting mimicking diet (FMD), Prolon.

Is the fasting mimicking diet helpful for fighting COVID-19 or boosting general immunity?

Dr. Valter Longo, PhD, shared his expertise about how FMD may help or harm specific patients or populations. 

Dr. Longo is one of the preeminent researchers focused on human nutrition, aging, fasting and caloric restriction. His lab at University of Southern California (USC) is among the select few centers in the United States granted funding to study the effects of diet in the context of viral infections. His lab completed preliminary work in mice and received funding recently to conduct human clinical trials. They will be studying immune function in elderly patients who have completed two rounds of the fasting mimicking diet.

I’ve had the privilege of meeting with Dr. Longo twice and we have been using the FMD in our clinic for two years. L-Nutra, the parent company for the FMD, donates 100% of profits to the Create Cures Foundations.

Can fasting improve immune response to COVID-19?

In his most recent comments, Dr. Longo highlights the complexity of this topic. We know that long-term, severe restriction of calories leads to immune impairment. However, short-term fasting mice are shown to have improvements in hematopoietic stem cells (in mice, these stem cells increase during the fast) as well as improvement in the neutrophil to lymphocyte ratio. The result is that mice get a rejuvenated healthy immune system.

In humans, Longo has measured white blood cell (WBC) levels during fasting mimicking diet and has observed a small but positive effect on WBC counts. Initially, the count goes down slightly, but after the 5-day FMD is completed there is improvement in neutrophil/lymphocyte ratios. This ratio improvement is associated with better resilience to stressors including infections. Much more on the N/L ratio here

Additionally, fasting is a safe way to intermittently suppress mTOR. The benefits of mTOR suppression are seen not only through fasting research but trials using the drug Rapamycin (mTOR inhibitor) for elderly patients which results in improved immune function.

Are you a good candidate for using FMD now?

This is a summary of Dr. Longo’s basic guidelines for fasting to improve resilience and boost immune function in this unique time. Want to hear the whole conversation? Click here.

  • If you’re at home, without symptoms, there is evidence to support that using the fasting mimicking diet, ProLon, will boost immunity.
  • If you are in the middle of an FMD and you start having symptoms of infection, he recommends discontinuing. 
  • If you have symptoms or feel run down, do not begin Prolon.

Other nutritional factors for improved immunity

Low glucose levels have been shown in human trials to improve immunity against viruses. Even if fasting is not the right option for you right now, Dr. Longo’s prudent recommendation for good immune function reflects the advice in his book, The Longevity Diet: Maintain balanced glucose and low-moderate protein levels. 

Waking glucose levels between 75-95

Glucose level 45-60 minutes after eating and between meals stabilizes between 80-110

Protein intake around 10-15% of your diet for healthy adults (excluding pregnancy) engaging in moderate activity between 18-70 years old.

Is time-restricted eating helpful?

Weight loss and glucose regulation are also beneficial for immune function. While most do not need to restrict eating to time-restricted eating, people that are overweight in the absence of hormonal imbalance can benefit metabolically from a 12-16 hour daily fast.

Prolonged 16-hour daily fasting can be detrimental, but in the short term, it is likely a safe way to normalize weight and blood sugar. The HbA1c (3-month blood sugar average), is typically improved in fasting and fasting mimicking diets. 

In our clinical practice we’ve observed that women in childbearing years (from adolescence to menopause) tend to benefit more from extending a 12-16 hour fast by eating an early dinner versus skipping breakfast. On the other hand, men and post-menopausal women seem to benefit from either.

Contraindications to ProLon 5-day Fasting Mimicking Diet:

  • Age <18 years old
  • Weight <100 lbs
  • Body fat percentage under 18% for women and 12% for men
  • Cardiovascular disease – talk to your provider
  • Pregnancy/breastfeeding
  • Diabetes – talk to your provider

Ongoing FMD research trials:

  • FMD with metformin
  • FMDs during chemotherapy
  • FMD for children with type I diabetes
  • FMD and cardiovascular disease
  • Effect of FMD on blood glucose and HbA1c levels
  • FMD and Multiple Sclerosis
  • FMD and Inflammatory Bowel Disease

If you would like more information, please contact us at

If you're interested in Prolon, buy it at a 10% discount.

Disclaimers: Jeff Grimm, NP-C, sells the FMD in his office and speaks for the parent company L-Nutra. 

About Megan Barnett, MS

Megan Barnett, MSMegan Barnett is a functional medicine practitioner in Portland, Oregon. In her clinical practice, she helps patients identify the root cause of their health problems, then designs individualized and evidence-based approaches to alleviate symptoms and help their bodies heal. She has a Bachelor of Science in Dietetics from Kansas State University and a Master of Science in Nutrition and Functional Medicine from University of Western States.