Real Life Extension: Caloric Restriction or Intermittent Fasting? (Part 2)


There are options for extending your life, but is it worth it? (Photo: Megan*)

This is the second half of our two-part article on real experiments (and successes) in life extension, authored by Dr. Michael Eades. Part 1 covers supporting research for caloric extension (CR) and intermittent fasting (IF).

Dr. Eades continued from Part 1:

We fooled around with a number of different eat-fast-eat regimens and came up with something that works pretty well. We set up our cutoff time as 6 PM. On the day we started, we ate until 6 PM, then fasted until 6 PM the next day. On the next day we ate supper right after 6 PM and ate breakfast and lunch (and a few snacks) the next day until 6 PM when we started fasting again.

The advantage of this regimen is that we were able to eat every day. One day we would get supper–the next day we would get breakfast and lunch. On no days would we go entirely without food. This schedule worked the best for us.

The big surprise in the whole process was how easy the whole thing was. We realized that intermittent fasting and dieting had opposing attributes and disadvantages. Diets are easy in the contemplation, difficult in the execution. IF is just the opposite – it’s difficult in the contemplation but easy in the execution. Here’s what I mean.

Most of us have contemplated going on a diet. When we find a diet that appeals to us, it seems as if it will be a breeze to do. But when we get into the nitty gritty of it, it becomes tough. For example, I stay on a low-carb diet almost all the time. But if I think about going on a low-fat diet, it looks easy. I think about bagels, whole wheat bread and jelly, mashed potatoes, corn, bananas by the dozen, etc. – all of which sound appealing. But were I to embark on such a low-fat diet I would soon tire of it and wish I could have meat and eggs. So a diet is easy in contemplation, but not so easy in the long-term execution.

Intermittent fasting is hard in the contemplation, of that there is no doubt. “You go without food for 24 hours?” people would ask, incredulously when we explained what we were doing. “I could never do that.” But once started, it’s a snap. No worries about what and where to eat for one or two out of the three meals per day. It’s a great liberation. Your food expenditures plummet. And you’re not particularly hungry. You’re either eating until 6 PM or you’ve got a meal waiting at 6 PM, so though it’s tough to overcome the idea of going without food, once you begin the regimen, nothing could be easier.

My wife and I fooled around with our regimen for a few weeks here and there just to prove to ourselves that we could live with it and that it was a doable strategy for just about anyone. We ultimately drifted back to our normal low-carb existence just because it seemed to work better with our schedules. It seemed that we always ended up with some kind of dinner engagement on the nights we were supposed to be fasting, necessitating a change in our fasting schedule.

Over the period that we followed the various IF regimens we lost a couple of pounds (we really didn’t have much weight to lose, nor did we have health problems that needed fixing) because, unlike the rodents, we couldn’t eat twice as much during the eating days as we would have eaten were we not fasting. We didn’t check any lab work to see if any values had changed. We weren’t doing a hard-core study; we were simply evaluating IF as a practical means for humans to use to improve their health.

I then wrote a blog post about IF that became the most commented post on my blog. It seems that the idea of IF had struck a chord with a lot of people, many of whom took up the torch and started IFing.

People started commenting that they were doing great on the IF. Some were losing weight, but others weren’t. Or if they were, they were losing much less than they thought they should be losing given the caloric reduction. As I mentioned, it seems that humans have a difficult time doubling up on calories on eat days, so in most humans an IF is also a reduced-calorie diet. And humans, it appeared, weren’t losing as much as their reduction in calories would predict. Reports started popping up on low-carb bulletin boards describing how blood sugar levels had gone up in people IFing and how some people had seen their blood pressure go up.

Like many of my readers, the research community had jumped on the IF bandwagon as well. And, in a similar fashion, the results were not all positive. Papers appeared showing that subjects IFing, or even regularly skipping a couple of meals per day, were developing insulin resistance, impaired glucose tolerance, elevated blood pressure, and decreased thermogenesis. Even Mark Mattson published a couple of human studies, including a randomized crossover designed experiment that showing the above disorders in women who ate the same number of calories in one meal per day as opposed to three meals per day.

I must hasten to add that the loss of insulin sensitivity, the impaired glucose tolerance and high blood pressure did not reach major levels. But they were significantly more pronounced than the same measures in the same subjects consuming the same number of calories divided into three meals instead of just one. The finding that troubles me the most, however, is the decrease in thermogenesis found under iso-caloric conditions. Said decrease in thermogenesis can only be worse in a true, real-world, intermittent fast in which the calories are typically lower than usual.

The decreased thermogenesis explains why the IF doesn’t work particularly well as a weight-loss regimen even though in most cases it is a reduced calorie diet [see the “the real science of fat-loss: why a calorie isn’t always a calorie” post for more on this phenomenon]. The subjects in these studies who consumed only one meal per day had reduced thermogenesis even while consuming the same number of calories that they did when eating three times per day. Imagine the reduction in thermogenesis if the calories were reduced as well as they are in most IF regimens.

The energy balance equation states that the change in weight equals calories in minus calories out.

Δ Wt = kcal in – kcal out

Many people think that the items on the right side of that equation are independent variables. In other words, if kcal in decreases weight will be lost because kcal out stays the same. But it doesn’t work that way because those terms aren’t independent variables – they are dependent variables. If kcal in goes down, often kcal out goes down as well to compensate. If people increase kcal out by exercising, they end up increasing kcal in because they eat more. It’s called working up an appetite. And since exercise doesn’t burn a whole lot more calories than simply sitting on one’s butt, it doesn’t take a lot of food to compensate. This effect is called adaptive thermogenesis. (Here is a full text article that goes into depth regarding the mechanisms involved.)

IF fasting, by significantly decreasing thermogenesis, decreases kcal out because our thermogenesis is what burns a whole lot of our calories. If the kcal in are decreased by the IF and the kcal out are decreased by the diminished thermogenesis brought about by the IF, it’s no wonder the IF doesn’t result in a lot of weight loss for most people.

The one question that remains unanswered is whether or not the intermittent fast followed in a low-carbohydrate way will lead to these same problems. To me, that point is kind of moot. Why? Because I looked at the IF as a strategy that allowed me to eat a lot of high carb foods that I would normally avoid and not pay the health consequences for it. If I’m going to limit myself to low-carb foods, why go on the IF? I can get the same results just following a regular, whole-food, low-carb diet without having to eat only every other day.

It’s looking like the intermittent fast is another of those ideas in science that looks good in animal studies then not so good in human studies, proving once again that rats and mice aren’t simply furry little humans. And it appears – for humans, at least – that the intermittent fast is indeed beginning to look like the reality of a late-night gimmicky infomercial: long on promises, short on delivery. I suspect that it is also a cautionary tale about the applicability of caloric restriction studies to humans.

Sorry to be the bearer of bad news, but that’s the way science sometimes works. Lab results and reality are often two different animals.

Guest writer biography: Dr. Michael Eades is one of the best-known bariatric (obesity treatment) doctors in the US and was the first doctor to introduce insulin resistance to the mainstream via his books, including the national best seller Protein Power.

Related and Most Popular Posts:
Real Life Extension: Caloric Restriction or Intermittent Fasting? (Part 1)
How to Lose 20 lbs. of Fat in 30 Days… Without Doing Any Exercise
From Geek to Freak: How I Gained 34 lbs. of Muscle in 4 Weeks
The Science of Fat-Loss: Why a Calorie Isn’t Always a Calorie
Relax Like A Pro: 5 Steps to Hacking Your Sleep
How to Travel the World with 10 Pounds or Less (Plus: How to Negotiate Convertibles and Luxury Treehouses)
The Art of Letting Bad Things Happen (and Weapons of Mass Distraction)

Posted on: March 3, 2008.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Comment Rules: Remember what Fonzie was like? Cool. That’s how we’re gonna be — cool. Critical is fine, but if you’re rude, we’ll delete your stuff. Please do not put your URL in the comment text and please use your PERSONAL name or initials and not your business name, as the latter comes off like spam. Have fun and thanks for adding to the conversation! (Thanks to Brian Oberkirch for the inspiration)

111 comments on “Real Life Extension: Caloric Restriction or Intermittent Fasting? (Part 2)

    • Probably, that is part of a reason that citing them so often as a source of knowledge of how we “ought” to live/eat/etc, does not make that much sense to me.


      • Well, yes and no. Understand that ‘lifespan’ as a metric averages how long each infant born to a particular population can expect to live. In other words, societies with high infant mortality rates can expect their ‘lifespans’ to come down quite a bit. Paleolithic man could easily live into his 60s, 70s, or even 80s, much like modern man can. But without prenatal care, hospitals, sterile delivery rooms, antibiotics, and starvation, infants were MUCH less likely to make it to toddler age.


      • Most humans died of early age due to problems with their teeth/mouth. Along with the reasons said above, I doubt anyone lived those high of years.


  1. Aloha!

    Kudos on EVERYTHING. My wife Anna and I have been living what we affectionately call “The National Geographic Lifestyle” for some time now, living in amazing places (Texas’ Big Bend region, Hawai’i), meeting amazing people (!!) and doing amazing things (!!!). We’re in the Puna district of the Big Island now, using T4HW as an instruction manual for a lifestyle we’ve been refining for years.

    You’ve nailed it, man. Maybe we’ll cross paths along the way.




    Hi Dave,

    Congrats on all, and thanks for the kind words! As for the offending content, I’m not sure what you’re referring to, but thanks all the same, I suppose :) Perhaps that was in response to another commenter…

    All the best,


    PS – We’ve removed the offending content from our website. Google had it flagged.


  2. I still believe there are just too many variables to an IF implementation to dismiss it. Such as could the person IF daily with shorter eating window? Could the person start 1x a week? How many meals does the person have in the eating window? Is the person eating healthy? Is the person eating junk food? Does the person exercise? Is it strength training? How often does one IF per week? Do you take weekeneds off? etc…etc…etc.

    That being said, IF works for some….and may not work for others. But there are always variables to change around and play with. I believe fasting must be a part of a person’s lifestyle for maximum health. Otherwise if you are always busy eating (which sucks up alot of the body’s energy), it takes away from the functions of cleansing, repairing and rebuilding cells? Especially in those that may already be at greater risk, toxic overload or have more damage that needs to be repaired?

    Alot of people doing exercise (CF especially) have seen positive results with the daily fasting of 15-18hours and eating Paleo type foods otherwise. There can also be advantages to that protocol M-F with the weekends off to enjoy more choices. Carb cycling can also be applied to the pwo workout window and/or high/low days.

    In the end. IF can work for weight loss if you are not eating crap and exercising. Eating healthy all day of course can also work for losing weight. IF gives other benefits to promoting life and disease prevention other than weight loss that something such as CR (calorie restriction) does not. One must modify IF to their lifestyle and goals. I just love not stressing about food all day long (but I also know how to eat healthy).

    Brain – Paleo man’s lifestyle was not based on cancer or heart disease. It was more because he got eaten by a tiger, broke his leg and starved to death, or some other thing that would be fixed by emergency care today or a quick trip to the supermarket. Had little to do with his long term health parameters.


    • I totally agree with this comment from Mike OD.

      Dr Eades even admits “I looked at the IF as a strategy that allowed me to eat a lot of high carb foods that I would normally avoid and not pay the health consequences for it.”

      IF will help with weight loss for some people (those not chunking up on high calorie processed foods when not fasting) and for those for whom weight loss is not an issue there is plenty of evidence to suggest a whole host of other health benefits contributing towards longevity and well being.

      Other rarely mentioned benefits which I’ve personally gained from IF:

      I no longer fear hunger. Hunger pangs are over within 5 minutes and in a 24 hour fast, once adapted, will only occur 2-3 times. This means there are plenty of other times on non fast days when I don’t immediately gobble the closest and most available food as soon as I’m hungry (often very unhealthy food if out and about at the time) and instead often choose to wait until I can eat something healthy.

      Rather than fasting in order to then eat whatever I want the rest of the time, I found I made much healthier choices throughout the week.

      I also massively reduced my portion sizes when I was eating, completely subconsciously. I just found I couldn’t stomach as much food in one sitting. I actually felt full and when full, able to stop eating.


  3. It seems that you’ve contradicted yourself. You say in Part I that you think the paleolithic diet is optimum for modern man, but then in Part II here, you say that you looked at IF as a strategy for consuming high-carb foods without paying for it. I think that you’ve sabotaged your dieting results.

    The thermogenic effects of eating a Paleo/Low-carb diet combined with IF should be the way to do it… not intermittent fasting between high-carb days. Going with the Paleo analogy, Paleolithic man didn’t eat bread and potatoes in between fasts, he gorged on more protein and fat.

    Also, it seems to me that the best meal to have on your one-meal days would be the morning meal, no? Fast between 9:00am and 9:00am…

    The article is still an interesting read, though. Thanks!


  4. Hmm. Interesting that when ‘part I’ (the “yay, we’re going to try IF” portion) was published, it got 25 comments, many extolling the benefits of IF.
    When ‘part II,’ by the same author, noting newer research and issues with IF and the possibility that “it appears – for humans, at least – that the intermittent fast is indeed beginning to look like the reality of a late-night gimmicky infomercial: long on promises, short on delivery. I suspect that it is also a cautionary tale about the applicability of caloric restriction studies in humans.”, somehow, the comment section and the chorus in support of IF goes silent.


  5. I don’t know much about IF, but I have some experience with religious fasting (24-26 hour fasts for Yom Kippur in Judaism; and my friends do sunrise-to-sunset fasting for Ramadan).

    Like I said, I don’t know about the heath effects. What I *have* noticed, from numerous yearly 24-hour fasts (sundown to sundown) is that by around 11 am on the day of the fast (ie: about 17 hours in), I get *extremely* hungry. At around 2 pm, the hunger goes away, but I become utterly incapable of any sustained mental focus. I can’t study, read novels, or do any of the other things that usually occupy my time.

    I can’t imagine doing this every other day. My productivity would plummet.

    Then again, I suppose other peoples’ mileage may vary. If it works for you, more power to you.


  6. On the contrary the Paleolithic man lived quite long. Take the Hunza Indians for example who lived over 100 and were reported to have erectile function @ 99. These beings lived without “modern society” and lived the “paleolithic” lifestyle. Much more on this topic can be read through the works of Westin A. Price in his book Nutrition and Physical Degeneration.

    Mr. Organic


  7. There’s a couple flaws in many of the animal studies. Rats generally are fed the same thing regardless of caloric intake. Humans, however, tend to eat poorer as calories go up. When we binge it’s usually pizza rather than grilled chicken.

    The other flaw is that most animals (and to some degree humans) are designed to eat all they can while food is available as they must prepare for times of famine. So the control group ends up eating way above maintenance calories. The reduced calorie group doesn’t get orca fat and therefore doesn’t get heart disease. Voila 20% longer lifespan.

    This doesn’t necessarily imply that an arbitrarily reduced calorie diet or periodic fasting is superior to eating a clean diet at maintenance calories (whole foods, higher protein, and less simple carbs).


  8. Hey Tim, what are you on Bryers-Miggs? There are tests online if you don’t know offhand.

    Curious if you are what I think you are (which I will encode below). The relevant question is whether your suggestions apply to all personality types, or whether you should, in the interest of correctness, claim a limited audience for your ideas.

    My guess for you (letters are shift twice right across keyboard such that an ‘A’ becomes a ‘D’). I encode it so that you can look at this AFTER testing yourself.



  9. Tim,

    I’m not trying to be overly critical, but I’m somewhat disappointed with this article. Part 1 was an exciting read, as IF seems to be a great discovery in life extension that many of us aren’t particularly aware of. Then I read Part 2, which discredits most of the supposed benefits of IF, and I wonder why you posted the article in the first place. I guess my question is, what was the purpose of this post?



  10. I agree. I was really excited about the implications made in the first post, and I consider you a reliable source Tim, so I trusted you. But this posting seems like a flipflop, and misplacing my trust always pisses me off.

    In future articles, will you say one thing, and then turn around and say another a few days later? Or is this a one-time deal?


  11. Tim,

    As I mentioned in a previous post, I’ve used variations of IF’ing, usually in the form of a 16/8 fasting/eating window. From the research I’ve found, it might increase insulin sensitivity for more favorable nutrient partitioning.

    IF’ing using a conjugated calorie scheme i.e. high carb, low fat on training days and low carb/higher fat/lower calories on non-training days, *should* keep insulin sensitivity high and maximize protein synthesis post workout (and new research showing an earlier protein synthesis peak in trained individuals).

    Assuming one hasn’t had psychological food issues in the past, this could be an effective tool in the trainee’s arsenal.



  12. Well, the humans didn’t do the study correctly so the data there seems pretty useless. Also, food quality is an issue. I’m not saying this to support IF but just to say the data looks shaky.

    By the way, the statement about exercising not burning many calories only applies if the exercise you’re doing isn’t building muscle. Something like unchallenging aerobic activity which many people think will help them lose weight and discover otherwise.


  13. The purpose of this post is just this: other peoples thoughts and opinions are just that. Also you should never be satisfied with what you know or have been initially told.
    Part one of the article was an introduction and brief reflection on a subject which may be new to many readers. Part two actually describes scientific data and results. All I’m saying about the information in part one is that you mustn’t read it like scripture. To support my second point I’d like to add that not even all the data from the studies were identical.
    So after reading both of these posts the reader will have a decent introduction and a basic understanding of the subject. Yet you shouldn’t feel as though that is all there is to know on the subject.
    One more thing; I agree with Allen about simply eating a clean healthy diet. I don’t know why things ever really have to be more complicated than that. Refer to Tim’s post here:How to Lose 20 lbs. of Fat in 30 Days… Without Doing Any Exercise.


  14. The only problems with diets like these is that they aren’t worth it. Severely cutting down on food fed to worms lengthens their life as well. It is a proven theory. The problem with not eating is that the quality of life becomes so low that those years aren’t worth living.

    Like the old joke: A guy walks into the doctor’s office. After being examined, the doc says, “I am sorry but you only have 3 months to live.”

    The guys asks if there is anything he can do to live longer.

    The doc replies, “You can quit drinking, smoking, and womanizing.”

    “Really? and that will help me live longer?” he eagerly replies

    “No, but you will sure feel like it.”


  15. So it looks like you’re saying IF is good for health/longevity/reducing appetite? But bad for weightloss?

    If so I should definitely give it a try. (always hungry and can’t gain a pound to save my life)