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Dr. Krista Varady Interview Part 1

April 7, 2010 Written by JP    [Font too small?]

I recently had the distinct pleasure of interviewing Krista Varady, one of the leading researchers in the field of alternate day fasting (ADF). By my count, Dr. Varady has co-authored six studies and two scientific reviews on the effects of ADF and caloric restriction in both animal and human models. In addition, there are several other trials that are complete and/or in the works that will hopefully be published in the near future. Dr Varady was extremely generous with her time and imparted quite a lot of information. So without further ado, here’s part one of my two part interview with Dr. Krista Varady of the University of Illinois, Chicago.

JP: What is it about alternate day fasting and caloric restriction (CR) that interests you?

Dr. Varady: Well first of all, I basically started out in my PhD program wanting to research lifestyle interventions to help prevent chronic diseases – so heart disease risk and cancer risk. When I first started, I was looking at nutraceuticals, so certain plant supplements such as plant sterols to lower cholesterol levels and help prevent heart disease. And basically, when I was doing these studies, I noticed that the people that were losing weight always saw the best changes in disease risk indicators. So that kind of spurred my interest in weight loss studies, and calorie restriction happens to be the main weight loss regimen.

JP: Can you help explain the distinctions between alternate day fasting and caloric restriction?

Dr. Varady: Caloric restriction is basically daily calorie restriction where an individual would restrict themselves by about 15% to 40% of their energy needs daily. So basically every single day you’re undergoing the same amount of restriction, whereas alternate day fasting involves a fast day wherein the individual would only eat 25% of their energy needs. So about 500 calories or so and that’s alternated with something called a “feed day” where the individual would eat ad libitum – so as much as they want. However in our studies we show that people end up losing weight because they can’t fully make up for the lack of food on the fast day on the feed day.

JP: Are you aware of any significant differences in how individuals experience ADF vs. caloric restriction?

Dr. Varady: What intrigued me about alternate day fasting was that it seems that people can actually adhere to it a little bit better than daily caloric restriction. So with daily caloric restriction you are restricting every single day and basically you end up going to sleep feeling kind of hungry. Where as with alternate day fasting even though you do undergo a really extreme fast day or extreme caloric restriction day you can always look forward to the next day. And you can pretty much eat whatever you want. I really do think it will help to increase adherence within these kinds of regimens, because with calorie restriction, adherence tends to drop off after about 8 weeks or so. That’s what’s been shown in a lot of studies.

JP: How long does it generally take for people to adapt to this new way of eating?

Dr. Varady: A lot of the subjects were saying that for the first two weeks it was pretty tough to basically change from a 3 meal a day eating pattern to just eating 1 meal a day and then 3 slightly bigger meals the next day. But they said that about after two weeks they totally got used to it and weren’t that hungry on the fast day anymore. They could undergo these really long periods of fasting without really feeling deprived. The other interesting thing that they were telling us was with regard to the feed day. The people didn’t binge. They only ate about 100% to 110% of their calorie needs.

Source: Obesity 2010 Mar 18. (link)

JP: I noticed a particular detail when reviewing your study that appeared in the March 18th edition of the journal, Obesity. In that experiment, the participants were required to eat only one meal on their fast days during the time frame of 12:00 PM – 2:00 PM. Is there a specific rationale for this?

Dr. Varady: The whole reason we even put a time frame in there was to control for the fasting period. It would be a slightly different study if we allowed them to eat the lunch time 500 calorie meal throughout the day. Their bodies wouldn’t go into a fasting state. We picked 12:00 – 2:00 because we wanted it to be right in the middle of the day. So they were waking up fasted and they basically had to wait a couple of hours until they could eat. If you give the calorie load in the middle of the day, it’s been shown to improve people’s work capacity. Whereas if you give them the meal right in the morning a lot of people will feel horrible by the middle of the day. It’s just from reading other fasting studies.

JP: Is it fair to say that you believe that the actual practice of prolonged fasting may impart added benefits beyond that of just reducing calories on alternate days?

Dr. Varady: That’s another study I want to design to see if we actually see different effects if we compare people on alternate day fasts that are consuming their meals within that amount of time (12:00 – 2:00) compared to people that are allowed to eat throughout the day. I think that if we did do that study, we’d actually see better effects from people doing the confined eating period. I think our bodies are used to that from the hunter-gatherer days where we’d have days of plenty where we could eat a bunch and then all of a sudden there was nothing out there and we’d have to fast. So I think our bodies are capable of doing that.

JP: I have one final question about the distinctions between ADF and CR. There have been numerous health effects associated with caloric restriction based primarily on animal studies. Can similar results be expected with regard to alternate day fasting?

Dr. Varady: With respect to heart disease risk indicators, we pretty much saw the same things happen. So we saw total cholesterol go down as well as triglycerides. And those are things we’re seeing in both the mouse models and in humans.

I’m going to end the first part of the interview at this point. Part two will focus on the past, present and future of alternate day fasting. Some of the topics that will be discussed will include anti-aging, cancer, cardiovascular disease, diabetes, exercise and the role that nutritional supplements could play in the context of ADF.

Note: Please check out the β€œComments & Updates” section of this blog – at the bottom of the page. You can find the latest research about this topic there!

Be well!


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Posted in Diet and Weight Loss, Interviews, Nutrition

38 Comments & Updates to “Dr. Krista Varady Interview Part 1”

  1. Nina K. Says:

    Good Morning, JP πŸ™‚

    great interesting interview, i’m excited looking for the next part πŸ™‚

    It seems (to me) that all studies about diet and nutrition drive us back to the basics: back to paleo and/ or a gatherer-hunter lifestyle πŸ™‚

    Greetings and stay healthy πŸ™‚
    Nina K.

  2. Linda Says:

    I have tried both alternate day fasting and calorie restriction (CR)and have opted for CR because, once I became accustomed to the routine, it became easier and felt more natural than a fasting-feeding regime. The important aspect of calorie restriction not mentioned here is that it is imperative that you have optimal nutrition at the same time as reducing your caloric intake. All in all, I find that by being properly nourished and being able to load up daily on substantial portions of vegetables and other healthy, low-calorie foods, I do not feel deprived or particularly hungry on CR. In fact, as so many CR practitioners report, one feels enormously energized.

  3. JP Says:

    Thank you, Nina!

    I tend to agree re: diets that return us to our historical roots (hunter-gather, whole foods, etc).

    I hope you’ll enjoy part two as much or more! πŸ™‚

    Be well!


  4. JP Says:

    Thank you for sharing your experience, Linda! Very interesting indeed.

    I have the same impression: If you’re going to participate in an dramatic form of caloric restriction or fasting, diet composition and quality become all the more important. Dr. Varady addresses that issue, in part, in the conclusion of the interview wherein protein and supplements are discussed.

    If you don’t mind saying, how long have you been on a CR diet? What types of changes have you noticed and have been evidenced in your blood work or other diagnostic tests?

    Be well!


  5. Nina K. Says:

    …i think people in japan/okinawa which follow the “eat-until stomach is only 80% filled” live automatically an CR lifestyle. despite that i find they live in a paradise they don’t need to die because they are already there πŸ˜‰ πŸ™‚

    Nina K.

  6. Larry Fratis Says:

    What an interesting post! I have always believed in the experience of fasting. Although I have fasted 3 to 4 days at a time in the past. This might be a great alternative for me.

    I have bookmarked your site. Thanks!

  7. JP Says:

    Thank you, Larry!

    If you try out ADF, please let us know your impressions about it – especially in comparison to your previous 3-4 day fasts.

    Be well!


  8. Linda Says:

    To answer your question, JP, I have only been on a systematic CR regimen since about the beginning of this year and intend having blood tests at the 6-month mark. I was not overweight before, with normal blood pressure, etc, but I am still interested to see the numbers on paper mid-year. Visible changes so far are: I feel marvelous and more alert, I have incredibly clear skin and eyes, I escaped a relentless round of colds and ‘flu this winter, and I am slimmer, trimmer and more energized than ever before (I am in my early fifties). True CR takes tremendous dedication and isn’t for everyone, but it suits me and I feel too good to stop now.

  9. JP Says:

    Good day, Nina.

    I suspect that’s part of the reason for their longevity – eating light and living in a relatively pristine environment. Generally speaking, I think they’re also very active, probably have higher sun exposure/Vitamin D levels and access to a fresh, nutrient-rich diet. All great things! πŸ™‚

    Be well!


  10. vadim Says:

    Wonderful interview! Very intresting, although I am a bit unclear how alternate fasting is done. Lets say you eat one meal at 2 pm. What would be considered fasting time wise? Would it be from 2 pm onward to what time? Next morning? How many hours is it that you have to fast before you start feeding on the next day? Am I making sense? Lets just break down two days of alternate fasting. I eat today at 2 pm a caloric meal in the amount of 500 calories. I am finished for that day is it right? Then I wake up the next day and what time should I be eating? Is it 12 hours window?

  11. JP Says:

    Thank you for adding that, Linda. I’m happy to know that you’re feeling energetic, happy and healthy while undergoing CR. That’s very encouraging.

    I hope you’ll stay in touch as time goes on. The results of your personal experiment (and your follow up examination) would be of great interest for many of us.

    Continued success and be well!


  12. JP Says:

    Thank you, Vadim!

    Here’s my understanding of how it works:

    Day 1 – Eat as you normal would.

    Day 2 – Eat one, normal-sized meal between the hours of 12:00 PM – 2:00 PM and nothing else until the next morning.

    Repeat the pattern.

    So, in terms of percentages it breaks down roughly like this:

    Day 1 = Eat 100% of your normal calorie consumption. In terms of calories, that might mean approximately 2,000 calories (as an example). However no calorie counting is needed.

    Day 2 = Eat about 25% of your normal calorie intake (within the specified, 2 hour window). Based on a 2,000 calorie-a-day model, your day 2 caloric intake should be around the 500 calorie mark.

    Repeat the pattern.

    I hope this makes sense. If not, please let me know.

    Be well!


  13. Sue Says:

    I find it easier to eat a dinner on ADF. Day 1 eat 3 meals, day 2 fast until dinner time or eat around 2pm and again at dinner – eat the same calories either in 1 meal or 2 meals on ADF. What do you think of the idea that fasting may contribute to gallstones. Not eating stagnates bile in gallbladder.

  14. JP Says:


    Prolonged fasting and quick weight loss appear to increase the incidence of gallstones in certain individuals. This is a significant concern in those undergoing gastric bypass surgery. However, it should be noted that ADF prompts other positive changes in the body re: gallbladder function. For instance, it improves insulin sensitivity, elevates adiponectin and reduces leptin levels.

    That said, I suspect it would be prudent to exercise regularly while engaging in ADF. I’m not suggesting anything too strenuous – even a moderate walking routine could be enough to reduce the risk of gallstones.

    Be well!


    Insulin resistance:



    Insulin Resistance Causes Human Gallbladder Dysmotility

    Increases Adiponectin and Lowers Leptin:







    Physical activity and decreased risk of clinical gallstone disease among post-menopausal women

  15. Sue Says:

    Thanks JP. So exercise increases the motility of the gallbladder.

  16. JP Says:

    That appears to be the case, Sue.

    Another good reason to exercise regularly. πŸ™‚

    Be well!


  17. anne h Says:

    They don’t die because they are already there– in paradise….
    What a great group of readers you have, JP!
    Love it!

  18. JP Says:


    I couldn’t agree more. I’m very grateful to have such a fantastic group of folks chiming in and tuning into my site. Case in point … you! πŸ™‚

    Be well!


  19. Larry Fratis Says:

    I think this is a great fasting program. I had been used to just fasting with water years ago. I felt good while doing so once I got used to it but recent findings have shown that may lead to dangerous consequences. I’ve tried this regimen for about a week now and I can’t believe the advantages to this as opposed to the
    previous. Thanks so much for the info.

  20. JP Says:

    You’re very welcome, Larry. I wish you continued success.

    Please report back with more details about your experience with ADF in the future.

    Be well!


  21. MP Says:

    I have tried limiting food, carb restiction, and ADF. I have found ADF to be the most effective and easiest to maintain over longer periods of time. I use a slightly modified ADF version, fasting every Mon/Wed/Fri of each week. I don’t fast on the weekends. It’s just too hard to manage. After the first week on and off any negative symptoms are all but gone. I have tried different fasting methods and this by far is the best. Also I find my problem with any diet is mental. Mainly stemming from boredom. Having 2 to 3 extra hours of day that needs to be filled has been and is my biggest challenge. Eating for some reason quells the “uneasiness” that overcomes me when I want or need a break from whatever it is I am doing. Plus my internal alarm goes off at the predicted brkfst/lunch/Dinner times. Physical activity helps during these bouts but nothing has topped eating. I have been doing ADF, on and off (no pun intended) for about 4 years. It certainly is the most rewarding and managable program for my lifestyle which consists of a lot of traveling.

  22. JP Says:


    Thank you for sharing your experience and technique with us.

    I find that drinking warm water which a pinch of sea salt helps me manage my own internal alarm clock. I don’t know if you and others will feel the same way about it. But for me, it’s quite soothing.

    Be well!


  23. Jiriya Says:

    Hi JP

    Love the website and the article.

    When will the 2nd part be available?


  24. Jiriya Says:

    No worries mate

    Just found it πŸ™‚

    Stay Blessed


  25. JP Says:

    Thanks, Jiriya! πŸ™‚

    Be well!


  26. Prabal Says:

    I do calorie restricted diet, by skipping the evening meals. Because after office (am in a high-stress job) I tend to eat a lot in the evening. I think I will try the ADF diet. I think Calorie restriction is a must for everyone ( not those who’re malnourished anyway, of course).

  27. JP Says:

    I wish you all the best, Prabal. I hope ADFing proves to be a winning strategy for you.

    Be well!


  28. Elaine Says:

    Great to read different experiences! I started 3 weeks ago after watching the Horizon programme…as a nurse and a colonic hydrotherapist it really ‘twisted my noddle’!!! Feel fab but only a couple of lbs gone….then saw people were only eating once a day whilst I’d spread my 450-500 calories over the day…Mmmmm, will try this way!

  29. JP Says:

    I hope changing to the once daily meal makes a big difference for you, Elaine!

    Be well!


  30. Kat Says:

    would you mind me asking if following this will effect a gallstone as i carried this many years left unopt because i was carrying twins. so would like to know as I know drastic dieting can cause problems just wondered would this be ok as it it feels something at last that i can follow as its not everyday.


  31. JP Says:

    Hi Kat,

    I’m unaware of any specific information about gallstone formation during intermittent or alternate day fasting. I know there’s a theoretical risk during extended fasts and a documented risk in times of significant weight loss (gastric bypass surgery, etc.). I’m sorry I can’t offer a more definitive answer at this time.

    Be well!


  32. JP Says:

    Updated 12/08/15:


    Eur J Clin Nutr. 2015 Nov 25.

    Intermittent energy restriction and weight loss: a systematic review.

    BACKGROUND/OBJECTIVES: Intermittent energy restriction (IER) is an eating pattern of regular daily periods of restricted energy intake followed by periods of unrestricted energy intake. This is gaining prominence as an alternative weight-loss strategy to daily energy restriction (DER). The aim of this systematic review was to determine the effectiveness of IER on weight loss in overweight and obese adults and compare this with DER.

    SUBJECTS/METHODS: A systematic literature search was conducted using the CINAHL, Embase, Medline, PsycINFO, Cochrane and Scopus databases. Eight studies that assigned overweight or obese adults to IER or to a DER ‘control’ were deemed eligible for inclusion.

    RESULTS: All studies reported significant weight loss for IER groups. Average weight loss was approximately 0.2-0.8 kg per week. IER resulted in comparable weight loss to DER when overall energy restriction remained similar between diets. The majority of studies that reported body composition outcomes have shown equal efficacy for fat mass, fat-free mass and waist circumference.

    CONCLUSIONS: Weight loss was achieved in overweight and obese adults following IER and this loss was comparable to a DER diet. IER may be an effective alternative strategy for health practitioners to promote weight loss for selected overweight and obese people.

    Be well!


  33. Pat Carnegie Says:

    Interesting information. This method reminds me of the fast walk/slow walk style of exercise which has been found to be beneficial. I am going to try this after researching caloric values of foods I generally eat and enjoy.

  34. JP Says:

    Hi Pat,

    Thank you. I think you may be referring to interval training? If so, I agree. There are some similarities – especially as they related to our ancestors. For most of the history of mankind, we ate and “exercised” based on availability and necessity. Oftentimes, that would mean great variability of food and movement.

    Be well!


  35. JP Says:

    Updated 06/02/16:


    J Nutr Health Aging. 2013;17(8):674-80.

    Efficacy of fasting and calorie restriction (FCR) on mood and depression among ageing men.

    OBJECTIVE: An intervention study on the FCR (Fasting and Calorie Restriction) dietary regime was carried out to determine its efficacy in improving mood states and depression status among ageing men.

    SUBJECTS: A total of 32 healthy males (MeanΒ±SD), aged 59.7Β±6.3 years, with a BMI of 26.7Β±2.2 kg/m2 were recruited to the study.

    METHOD: Participants were randomized to either the FCR group (and were instructed to follow a calorie restricted dietary regime with intermittent fasting) or to the control group (in which individuals were asked to maintain their current lifestyle), for a 3 month period. Mood was assessed using the Profile of Mood States and depression was assessed using Beck Depression Inventory-II and Geriatric Depression Scale-15 at baseline, week 6 and week 12 of the intervention.

    RESULTS: A total of 31 subjects completed the study (n=16, FCR and n=15, control). Significant decreases in tension, anger, confusion and total mood disturbance and improvements in vigor were observed in participants in the FCR group compared to the control group (p<0.05). No significant changes in mean depression scores were observed. Weight, BMI and percent body fat were reduced by 3.8%, 3.7% and 5.7% respectively in the FCR group.

    CONCLUSIONS: Our findings show that a FCR dietary regime is effective in improving mood states and nutritional status among ageing men.

    Be well!


  36. JP Says:

    Updated 06/05/16:


    Cell Rep. 2016 May 25.

    A Diet Mimicking Fasting Promotes Regeneration and Reduces Autoimmunity and Multiple Sclerosis Symptoms.

    Dietary interventions have not been effective in the treatment of multiple sclerosis (MS). Here, we show that periodic 3-day cycles of a fasting mimicking diet (FMD) are effective in ameliorating demyelination and symptoms in a murine experimental autoimmune encephalomyelitis (EAE) model. The FMD reduced clinical severity in all mice and completely reversed symptoms in 20% of animals. These improvements were associated with increased corticosterone levels and regulatory T (Treg) cell numbers and reduced levels of pro-inflammatory cytokines, TH1 and TH17 cells, and antigen-presenting cells (APCs). Moreover, the FMD promoted oligodendrocyte precursor cell regeneration and remyelination in axons in both EAE and cuprizone MS models, supporting its effects on both suppression of autoimmunity and remyelination. We also report preliminary data suggesting that an FMD or a chronic ketogenic diet are safe, feasible, and potentially effective in the treatment of relapsing-remitting multiple sclerosis (RRMS) patients.

    Be well!


  37. JP Says:

    Updated 09/06/16:


    Obesity (Silver Spring). 2016 Sep;24(9):1874-83.

    A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity.

    OBJECTIVE: To evaluate the safety and tolerability of alternate-day fasting (ADF) and to compare changes in weight, body composition, lipids, and insulin sensitivity index (Si) with those produced by a standard weight loss diet, moderate daily caloric restriction (CR).

    METHODS: Adults with obesity (BMI β‰₯30 kg/m(2) , age 18-55) were randomized to either zero-calorie ADF (n = 14) or CR (-400 kcal/day, n = 12) for 8 weeks. Outcomes were measured at the end of the 8-week intervention and after 24 weeks of unsupervised follow-up.

    RESULTS: No adverse effects were attributed to ADF, and 93% completed the 8-week ADF protocol. At 8 weeks, ADF achieved a 376 kcal/day greater energy deficit; however, there were no significant between-group differences in change in weight (mean ± SE; ADF -8.2 ± 0.9 kg, CR -7.1 ± 1.0 kg), body composition, lipids, or Si. After 24 weeks of unsupervised follow-up, there were no significant differences in weight regain; however, changes from baseline in % fat mass and lean mass were more favorable in ADF.

    CONCLUSIONS: ADF is a safe and tolerable approach to weight loss. ADF produced similar changes in weight, body composition, lipids, and Si at 8 weeks and did not appear to increase risk for weight regain 24 weeks after completing the intervention.

    Be well!


  38. JP Says:

    Updated 08/10/17:


    Nutr Diet. 2017 Aug 9.

    Is two days of intermittent energy restriction per week a feasible weight loss approach in obese males? A randomised pilot study.

    AIM: The 5:2 diet (two non-consecutive days of 2460 KJ (600 calories) and 5 days of ad libitum eating per week) is becoming increasingly popular. This pilot study aimed to determine whether the 5:2 diet can achieve β‰₯5% weight loss and greater improvements in weight and biochemical markers than a standard energy-restricted diet (SERD) in obese male war veterans.

    METHODS: A total of 24 participants were randomised to consume either the 5:2 diet or a SERD (2050 KJ (500 calorie) reduction per day) for 6 months. Weight, waist circumference (WC), fasting blood glucose, blood lipids, blood pressure and dietary intake were measured at baseline, 3 and 6 months by a blinded investigator.

    RESULTS: After 6 months, participants in both groups significantly reduced body weight (P = <0.001), WC (P = <0.001) and systolic blood pressure (P = 0.001). Mean weight loss was 5.3 ± 3.0 kg (5.5 ± 3.2%) for the 5:2 group and 5.5 ± 4.3 kg (5.4 ± 4.2%) for the SERD group. Mean WC reduction for the 5:2 group was 8.0 ± 4.5 and 6.4 ± 5.8 cm for the SERD group. There was no significant difference in the amount of weight loss or WC reduction between diet groups. There was no significant change in diastolic blood pressure, fasting blood glucose or blood lipids in either dietary group.

    CONCLUSIONS: Results suggest that the 5:2 diet is a successful but not superior weight loss approach in male war veterans when compared to a SERD. Future research is needed to determine the long-term effectiveness of the 5:2 diet and its effectiveness in other population groups.

    Be well!


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