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Fast-5 = Calorie Restriction?

Calorie restriction—defined as limiting an animal's intake to some fraction of what it would eat given the opportunity to eat without restriction ("ad lib")—has been shown to prolong healthy lifespan, reduce inflammation, increase resistance to cancer growth and more. You can read more about calorie restriction (CR) in this recent Time article.

To achieve these benefits, some people self-impose a calorie intake limit, and various ways of doing this have been endorsed (The Longevity Diet, The CR Way, and Alternate-Day Diet). Different ways of achieving similar results through intermittent fasting have also been suggested, including the Fast-5 Diet, the QOD Diet and Eat-Stop-Eat.

Of these, Fast-5 uses the shortest fasting interval (19 hours) and a regular daily schedule. The results of the alternatives appear comparable, so I suggest people go with whichever option works best for his/her schedule. One of the notable aspects of Fast-5 is the appetite correction that occurs in maintenance phase—people tend to remain at a stable weight without counting calories. In my experience, that level of calorie consumption is substantially lower than what I ate when I was eating on an ad-lib schedule. How much lower? I have to guesstimate because I didn't count calories back then (nor do I now.)

What I eat now seems to average 500-700 calories less per day than what I used to eat when I ate ad-lib with three meals a day. Out of a total calorie intake of 2000-2500 per day, that amounts to a cut of 25-35% per day, which puts it in the realm of significant calorie restriction. Since it's relatively easy to do, Fast-5, which is encouraged for weight loss and weight maintenance, may make anti-aging benefits of CR (and intermittent fasting) accessible to a much broader population than the CR alternatives above, and that would likely help a lot with heart disease and other chronic diseases associated with advancing age. What has your experience been?


I don't count calories either, but I think I'm eating at least 500-1000 fewer per day. I've been maintaining a healthy weight for about a year now, using Fast-5 (I originally lost ~25 pounds in 4 months of F5). My former diet ALWAYS had ~500 calorie breakfast (cold cereal, milk, OJ), snacks and a smallish lunch, then eat like crazy in the evenings. Now I just eat like crazy in the evenings and fast the rest of the time. It is surprisingly easy to do.

I haven't been counting calories either. I just try to put healthy stuff in my body as much as I can.


I started fast 5 2 days ago. I eat for 5 hours in the morning and stop after lunch. It works good for me to far. I intend to keep you inform as time goes on.I feel like I sleep a little better.

I use Fast-5 with calorie limitation. I prefer that phrase to calorie restriction, which somehow evokes in my mind an image of starving Auschwitz victims. My goal is to lose 1% of my current body weight each week. I wrote a simple Excel program to give me the goal for each week, and for the past 7 months I have been "on chart."

Currently, I eat 1000-1100 cals/day, all taken at one very enjoyable luncheon seating where I eat slowly for a whole hour. Very pleasant. I do not feel deprived or unhappy. I do take note of the grams of protein (I try for 45) and of fiber (I try for 21); but that is not always to achieve. So about once or twice a month, I may have an "All Fiber Day" or an "All Protein Day," always adhering to the calorie limit. Yes, I'm occasionally hungry, but that seldom happens and besides, hunger never killed anybody -- except those aforementioned Auschwitz victims.

Love Fast-5.

Linda in Amarillo


I was wondering if you'd be willing to share how you did the excel program? I am somewhat versed in stats and excel, and this sounds like a great way to monitor progress!

Rachel in Chicago

Over the average, I think I am consuming some less calories. If I binge, probably Im not. But, before Fast-5 I would eat almost all day long. Often with multiple binges, eating sugar, and carb loaded snacks almost contuniously sometimes. But now, I dont have the chance to do that. If I try to only eat until I am comfortably full, I would say that Fast-5 Cuts my calories consumed between 25-40% + less than I would be eating if I was eating normally. I dont count calories much, so I wouldnt know what my normal would be.

I'm a week into trying the 19hr daily fast & it has been easier than I thought it would be. However, my friends & family think I'm nuts. This just shows me how crazy our society's attitude is toward food (must have breakfast, 3 square meals, etc.).

Also, I think I'm liking the other health benefits of CR more than just the weight loss.

Thanks Bert!

Yes, even my dr thought I was nuts when she asked what I had been doing (that was in March!) When I went back in October, she just marvelled at the continued slow loss, and I think, that I had stayed with Fast-5! She has been my (trusted) primary care physician for 22 years! Glad she gave me such a hard time about needing to lose!


I'm curious as to what the other health benefits are that you're experiencing?
I know what you mean: my family seems very concerned and think this diet is unhealthy. I can only go by the fact that I feel better!

I started this because I tend to skip breakfast and usually break my fast around 11-1. I have lunch at one. I found it easy to simply do what I always do and start eating lunch at 1 and have my dinner at 5. My preferred eating time is 1 to 6. I simply just stop eating after 6 when sometimes I would have snacks. I don't think I could wait until 5 since it does not fit in with what I have been doing naturally and I think I will feel deprive and ultimately fail. So far I don't feel I am "dieting" but simply being more mindful of when I start to eat and when I stop. Already the urge to gorge during this time period is lessening since I eat what I have normally eaten and I feel sated (takes me a long time to feel hungry after a meal anyway). So if I set my window from 1-6 does that make any difference since I am still fasting 19 hours?

I'm doing well with me eating time from 5 to 10 P.M. I usually skip breakfast because I go out the door in a hurry, and was never a lunch eater. I like to snack at night so the 5 to 10 windows works well. I think its important to follow your lifestyle when you
select your eat time. Plus I noticed my appetite has lessened since I started the fast5 three weeks ago.

Yes, as you said, any window you use that leaves the 19-hour fasting period intact should work. This question is discussed in more detail along with other questions that may be helpful on the FAQ (Frequently Asked Questions) page.

i tried f-5 for a few months a couple of years ago; i discontinued basically b/c every day, when eating time finally came i was ravenous & would eat even more than everything in sight; yet next morning i was feeling weak & lazy & discouraged (even my eyes were getting weak & lazy)
back then i was eating, as i recall, something like 5-8 or 6-9 pm, just b/c some people had said that evening eating was best
when i gave myself permission to eat whenever i felt like it, i found out that most of the times my ideal meal time was at about midday
so now that i feel like trying f-5 again (seeing the failure of other foodstyles), i'll see what type of schedule i end up following -- i tend to think that i'll be eating something like 11-4 or 12-5
we'll see how things unfold

i appreciate everyone's presence here; thanks & be well

so now i've been eating 2 meals daily: lunch sometime 12-2 pm & dinner at ~4 pm

in my fasting window i drink (1-3) yerba-mate teas ad lib & this seems to be making a huge difference in my experience: i'm not a zombie in the morning any longer as i was the 1st time i tried f-5

thanks & be well

Please tell me more about Yerba Mate. What brand, how to prepare, etc. Thanks, Alan


I love yerba mate! I've lived in Argentina where the drink is a big part of everyday life. I agree with rafonly's comment that it gives a nice energy boost, without any crash that is typical with other caffeinated beverages.

There are two forms of yerba mate: loose leaf, and in tea bags. The easiest way is to buy the tea bag version. Search for yerba mate, and look for "mate cocido." You prepare mate cocido like other teas. Heat up some water near boiling, let it steep for a 3-5 minutes, and it's ready to drink. I found that I like the brand cruz de malta, but I'm sure other brands are good, too.

If you want to be adventurous you can try the loose leaf kind. You'll want to pick up a mate (the gourd cup) and a bombilla (the straw that filters).

For doing fast 5, if you are consuming outside of your feeding window you'll want to avoid adding any sugar to the drink. Be prepared for a bitter drink. That's not for everyone, but I like it even without any sweetener.

Best of luck,
Jon G

Hi, i've recently joined this website and got greatly interested in Yerba mate tea. but i've found out that drinking this tea can increase risks of various of types of cancer? do you know anything about that?
i'm confused!

I would want to see the studies. This sounds dubious, if not ridiculous. Notice she said the cancers were greatly increased in those who also smoked. Duh!!

heysuze's picture

I seem to recall it had to do with how the raw material was partially smoked when drying it. They initially thought the cancer causing effects might be avoided by limiting the temperature of the brewing water to less than 150 degrees, not boiling hot, but now I am reading this may not be true.

I'm sure the flavored yerbe mate has calories, but not the tea leaves themselves.. yerbe mate is full of anti oxidants... I've only heard how good it is for you.

Yerba Mate contains calories (at least the Guayaki loose-leaf brand). Only 10 per serving on my bag, but that's still something. I just started researching Intermittent Fasting, so I apologize if I am misinformed... but I have read that consuming any calories during your fasting period will lower the effectiveness of the fast. This is why drinking juice during fasting periods is not recommended.

Again, I hope you'll correct me if I'm wrong, but I believe you're only supposed to consume water and teas without sugar/calories during the fasting period.

have you or someone else written on the epigenetic impact of f-5?
i'm interested in studying nutrigenomics at grad level (for future research) & tend to think that f-5 must have an impact on the modulating of a person's gene expression

can you share your ideas & experience in this regard w/ us?

thanks & be well

For those reading this who don't know what epigenetics is, I include a brief description. Epigenetics is the study of how DNA is packaged and modified inside cells. While the sequence of the DNA remains unchanged, the packaging and other epigenetic modifications change the accessibility and use of the genes encoded in the DNA. All of an individual's cells have the same DNA sequence except the germ cells (sperm and egg) and cells that have DNA rearrangement mechanisms such as T cells in the immune system.
In order to make one cell (the zygote, the union of sperm and egg) into many different kinds of cells, modifications are made to which genes in the DNA are expressed (copied and used for making protein). Stem cells, which can become many different kinds of cells, thus become differentiated into the specialized cells like muscle, nerve, skin, bone, fat, liver, etc. Once differentiated, cells do not typically have the ability to de-differentiate to become stem cells again.

Epigenetic changes can control gene expression, but they're not the only way those changes can be initiated. Signals passed via transcription factors can also alter gene expression by increasing or decreasing the number of RNA copies made from a DNA gene. Other factors like microRNAs can also influence gene expression.

I do not know of any specific evidence indicating that Fast-5 results in epigenetic changes rather than from changes in conventional cell signaling through hormonal changes. However, investigation of epigenetic changes that result from caloric restriction (CR) is relatively recent and unfolding. In some animal experiments, CR applied at one time appears to make a difference months to years later, suggesting epigenetic changes have occurred. The similarity of changes that occur with Fast-5 to those occurring with caloric restriction suggests that some of the mechanisms behind the observed changes may be shared. Epigenetic changes, therefore, may be playing a role in some of the changes observed following a switch from conventional eating to the Fast-5 program, but it will take research focused on this question to answer it with certainty.

is there an easy to understand answer to what these changes were?

Could you explain what changes you're talking about? Are these positive or negative changes? Thank you.

All the changes I know of that are associated with fasting are beneficial, and we're talking about minor changes like more emphatic sense of satiety (fullness), decrease in appetite, and a feeling of more energy. Any change in the body could be based on an epigenetic change, but until researchers look specifically, we can't know exactly what is at the root is of a change. The changes may be due to an alteration in hormonal balance, or they may be a change in how a control organ such as the hypothalamus is giving signals. Within the control organ, cells are doing something differently. Those changes in the cells suggest there has been a change in which proteins and how much of each protein the cells are making from each gene (a gene is a "protein recipe" contained in the DNA cookbook). Those changes can happen as a result of different stuff sticking to the DNA causing the cell to make more or less of different proteins, or a result of how the DNA is packaged (epigenetic change). Whether the change is the result of hormonal balance, gene expression control, or epigenetic doesn't really make a whole lot of difference. The only reason epigenetic changes are noteworthy is that epigenetic changes are a recently discovered mechanism of gene expression control.

I have tried them all. Atkins, Sommers, weight watchers, etc. I started Fast 5 two days ago and so far it is surprisingly easy. A little growling at previously normal meal times, but nothing bad or uncomfortable. I honestly think this is the answer for me. I am 58 yrs and need to lose about 65 pounds. I do work out with resistence training and moderate cardio. I have been successful with the previous diets, but whenever I relax them the least, the weight comes steadily back. This is a program I think I can live with. There is no question that diet trumps exercise for weight loss. I am looking forward to seeing how this works out, and I hope to keep you posted. Thanks.


Welcome to Fast-5. This group has lighter traffic than the Yahoo group, which has a link on the home page. It sounds like you know what to do and you're on your way. Please make sure you read the summary and FAQ pages here, and don't be surprised if you have a tough day in a day or two--it gets better quickly after that. Good luck and best wishes!


Thanks for the welcome. I finished my fourth day and I have to admit it was a little tougher today; midday I started thinking more about food. I did hold out and did ok, a reasonable meal about 6pm and filled up. My question today is how do I handle the scheduling of my fasts. I am doing ok during the work week, but can see problems with the weekends and upcoming Thanksgiving holiday, etc. If I go ahead and revert to 2 or 3 meals on the weekends, does this reset my fat mobilization back to square one? Do I need to go at least two weeks before I "relax" the fasting program? I really hate to take 2 steps back, but with family, holidays, etc. I am in a quandry. Thanks for any advice.


Hello Bob'sbigboy,

I have found that moving the feeding window around from day to day is not an issue for me. During the week, i have a feeding window between 12noon and 4pm. On the weekends I usually switch it to 5pm-10pm. If there is a breakfast scheduled on Sunday morning, for example, I switch it again to be in the morning.

During Thanksgiving, just switch your eating window to fit the schedule of your dinner and eat and enjoy with your family. One thing you might try is to add in a longer fast the day before or the day after Thanksgiving. Kind of a mix between Fast-5 and Eat, Stop, Eat. It is very easy to overeat during a Thanksgiving type dinner so if you incorporate a long fast before or after the dinner you can help to balance out your calories. Think of your allotted calories as PER WEEK rather than PER DAY. I do an all day fast of around 38-40 hours before a big event. This means that I would eat normally two days before the event and stop eating at the scheduled time. Then, the next day, I would fast all day and all evening, not eating at all, just water and tea. The next day would be the big event and I would break my fast during that meal and not worry.

The great thing about intermittent fasting is that you can adjust it to fit your schedule rather than trying to adjust your schedule to fit it.

I am definitely eating less in my opinion. I have been on fast-5 for a couple weeks and I was about 165 when I started and am about 160 now. When I was pre fast-5, I was having a couple eggs for breakfast, snacking on peanuts through the day and having a lunch of one double cheeseburger... the mcdouble ... maybe without the bun. Then for dinner having what my wife cooked. Now I have omitted the snacks on peanuts, the eggs and the double cheeseburger. For dinner I have what my wife cooks (albeit sometime I do have seconds and feel I overate... I feel more senstive to that now). In the beginning of fast-5, I was having more during my window but now I don't seem to be doing that as much as I am recognizing it just makes me lose weight faster if I don't overindulge and its not that uncomfortable as I don't feel any more hungry after dinner than I do during the day so am thinking of just limiting it to my dinner. That means that I end up with a 23 hour fast instead of a 19 hour fast. I don't know if that means anything at all, as far as having more fasting time, but it seems doable. What concerns me with it though is I am sure I am not eating that many calories. Certainly not the 1500 that people recommend you get every day even while dieting. Regardless it seems to work. I also do weight lifting exercises in order to maintain muscle mass (heavy weights with low reps). Since starting fast five, my waist has gone down at least an inch, maybe two. I am starting to consider waist size vs. BMI or weight as I have seen studies that correlate waist size to fitness. I am 55 years old and the 34 inch waist pants are feeling generously sized or basically a perfect fit for a thin person--not tight at all. Well I do weigh 160 and that is the limit for me as 5'7 charts and BMI do say that over 160# is considered overweight. Interestingly its also the weight where my waist to hip ratio goes into a good category. When I started to diet and my clothes started to loosen, I found a fear factor that I was getting weaker or withering away. This is weird but I think its because the general population is so husky nowadays that normal weight people appear to be weak and scrawny. I am getting over this fear and its also part of the reason I began lifting heavy weights for low reps, to be sure I don't lose to much muscle. I am hoping to get so I can wear 32 inch pants and then see how that goes and I imagine I will just keep on fast-5 forever. My targets are 158, 155 and then 152. It seems by the charts my optimum might be 148 or 147. Yesterday I heard Richard Simmons on Fox News talk about how he was about 160 and then reduced down to 135. He is a half inch shorter than me maybe so its interesting that is also the weight I landed at when I was in the Navy and did a two month fast while on a submarine tour. After getting to that weight, exercising became a piece of cake. I immediately took up running when I got back from patrol and was able to start with five miles a day. I will see what its like to be 148 I have no clue what my final goal should be or if I need a goal. I do know when I was 145 getting out of navy bootcamp I was not lean really so a low weight might not be bad for me given that I have tiny wrists. I am not large frame but might be medium. Now that I see the fallacy in the diet and exercise recommendations out there (eat all day etc.) , I am starting to doubt almost anything people have to say on weight, diet and fitness. So far so good!

ham.in_acan's picture

Dear Bert Herring, M.D.

I wanted to Thank You for creating the Fast 5 plan and sharing it for free, you are a Saint! I want to donate as soon as I can.

I just started Fast 5 on Wednesday using calorie restriction of 1200 calories and just started adding 20 minutes of exercise daily. I have become an expert in counting calories down to the tenth of a calorie. I weighed myself this morning and found I lost 2 pounds in 2 days. You can’t imagine how happy that made me. :) Especially, when I have been dieting and losing 1 to 2 pounds a week. I was hoping Fast 5 would speed up my weight loss. I do feel different since I have been practicing the Fast 5 plan. I found I don't want to eat as much and I don't miss it. The first day was more of a mental challenge than physical one.

I really like the definite guidelines of when to start eating and when to stop eating. I find by eating in the 5 hour window that I can reach that "maximum fullness" that I sometimes crave and still have food left over. Yesterday, I had to force myself to eat my daily calories of food and ended up having some food left over.

I usually plan my meals in advance before I was having breakfast, lunch and dinner. Now, I just squish all those calories into a 5 hour window. I do try to nourish my body with the proper nutrients and don't have many bad vices. I drink mostly water and eat whole foods, fresh fruit and vegetables. I was lucky to have a mother that taught me how to like almost all vegetables.

At one time I did fall into the processed foods, white flour, white sugar, butter and the red meat trap. Now, I have read enough reliable information to prove to myself that those foods are really not that good for my arteries or much else. I still eat meat but tend to stay more with turkey, chicken, fish or use boiled egg whites as my protein.

Today is the first day I felt like I could REALLY succeed. I felt like I could control my diet and calories and achieve the weight loss I desire and maintain it. You don’t know how important that is to me. It’s like passing a mile stone. Something mentally and physically just clicked for me. Thank You again Dr. Herring for creating a great program!


Joan Zanetti

I went to a bookstore and asked the saleswoman, "Where's the self-help section?" She said if she told me, it would defeat the purpose. --George Carlin

You're welcome, and no I'm not a saint. What I'm sharing would be widely known if the public were not inundated with money-driven misinformation that compels people to eat, eat, eat. Please do not expect the rapid weight loss you've seen over a couple of days to continue at that rate. That weight is mostly water and has to go some time, and it's a nice way to start, but that rate can only be sustained in real fat loss with massive energy output. Each pound of fat accounts for about 3500 calories. Two pounds per day of fat would require a calorie deficiency of 7,000 calories, which is enough energy to run 70 (yes, seventy) miles and most people just don't put out that much energy in a day, so that much fat would not be burned even if no food were consumed at all. A deficiency of 500 calories a day, however, is manageable (with some help from the appetite center).

The weight loss you described of a pound per week is really good -- IF it can be sustained. That means 52 real pounds per year. The key is sustainability -- can you live with it? Most people who try Fast-5 find that they can live with it and feel better doing it than they do on a conventional eating schedule.

One of the keys for Fast-5's effectiveness is that it controls intake by getting the appetite system working like it should. If you don't want food, you don't have to will-power fight to avoid excess intake. Give it time and let your body adjust. You're more than a few days into it by now, so the hardest part should be behind you.

Best wishes for your success!

I just heard about the Fast-5 program as I was continuing research about the benefits of intermittent fasting.

I guess I'm in the "Building Up" phase because I'm still only fasting 16 hours... 8PM till noon the next day (or perhaps 12:30).

It seems like after that, I get light-headed, etc. Not sure if I'll be able to build up to the 19 hours (and hadn't originally thought about it since my IF plan was to go 16/8.)

But, even at this level, I've experienced what you're talking about... I already feel better and have more control over my eating.

Your point about breaking your fast with a highly nutritious food was very well taken.

I'd tried the "Alternate Day" fasting but breaking the fast daily seems to work best for me. After reading Eades' article on this fasting study, I knew I'd have to go at least 16 hours.

Whatever I end up with, I feel much better overall and have noticed improvement in just a very short time.

Thank you for your work.


Im confused. Reading all the posts I am confused wether you should only eat 1 meal a day or eat until full in your 5 hour window? It makes sense to eat one meal to lose weight, of coarse you will, but I thought the beauty of fast 5 was you have no restrictions in your window if you just have the will power to get through the 19 hour window? I am on day 11. I started at 132 then have been fluctuating down, knowing mainly water weight when I lost 4 pounds. My current weight is 130. I changed my window to 4-9 which seemed to work better with my family. I eat a snack at 4 so Im no ravenous by dinner at 6, then usually have another snack at 8. Im worried I may be eating too much? My food is definstely not perfect choices. Example. Yesterday I had a small bag of Doritos to hold me over. Dinner was steak with asparagus with hollindaise sauce sweet potatoe a salad and garkic bread. Then my dessert later was a piece of coffee cake with tea. I never eat these things. I think Im over indulging? I also work out 1 hour per day. Combination of weigh training and cardio. Any suggestions?

For most people, it doesn't matter. One can snack, then have a meal, or have a meal, then snack, or graze through the window, or have two smaller meals at the beginning and end of the window. The point is to follow your appetite -- if you feel like eating a meal, have one. If not, have something smaller.

What's important is what works -- as long as your routine is working for you then keep it up. When it doesn't work, it's time to try something different, like focusing on one meal, or a shorter window or whatever. At 11 days, you're just getting started, so give it a couple of weeks and see if you fall into a routine that's comfortable and you lose weight at a pound per week or better (if you have that much to lose).

With Fast-5, a key change is appetite, so however you choose to eat usually turns out to be okay because you take in the same number of calories. How the fasting period enables the body to adjust appetite appropriately isn't clear, but that appears to be what is happening. This enables one to be flexible with eating, and that's a plus. The less rigid we are about what we intend to eat, the more we can listen to our appetite and eat the proper amount.

Food choices can help a little because a heavy carb intake tends to make hunger more prominent the next day.

I have been praying about doing another Daniel Fast (21 days, no meat/dairy/animal products/eggs, no sweeteners of any kind, no "precious foods" (like honey); Allowable foods include fresh fruits and vegetables, whole grains, legumes/beans/nuts/seeds, and drink only water), and I was wondering how the two taken together might affect a person? Would you recommend starting the Fast5 first, then after a week or two starting Daniel?

Another thing I am curious about is what happens when you throw coffee into the mix. I am not a big fan of tea, but I LOVE coffee (black, of course). The last time I did Daniel, I was faithful for 9 of the 21 days (but I kept my coffee...) and I lost 11 pounds. On day 10 I ended up with a plate of buffalo wings in front of me and just couldn't resist! :) Oops!

Thanks for all of this information! I am truly fascinated!!

I started the fast-5 on sunday 3 days ago, ive chosen to eat between 2pm and 7pm as I work nights from 9 till 5 then sleep roughly 7 hours so these 5 ours are pretty much when I would eat anyway just had to put off breakfast/dinner till 2. so far i'm finding it easy to stick to few rumbles in the stomach while on break at work and first thing when I get up but nothing I cant ignore suppose its just my body getting used to the new eating times. im looking for a drink that doesn't contain calories that I can drink throughout my fasting 19 hours if anybody knows of any as ive only been having water but not a great fan of it on its own. also Ive read that on the fast 5 for two consecutive days between your 5 hours eating your calorie intake should be around 500 is this right or just eat the same sort of amount all week?
thanks for any help any one can give, I want this to b a success.