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)

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

  1. I have been doing my own version if IF for about 5 years now, and it has worked very well for me. I began ding it after reading Dr. Eades blog on this subject.

  2. Dave, I’d love it if you’d take a look at this… and willing to hear from anyone who feels familiar enough with the benefits of IF to chime in as well.

    I’ve been doing a decent amount of “16hr fast / 8hr eat” cycles. (My intention is to do 6hr eat window – but somehow, not quite gotten there yet.)

    (Oh, I should note, I do drink Organic Coffee and Coconut Oil most of the time when I’m fasting – I’m not sure if the butter here in Costa Rica is grass-fed or not — unless I buy straight from a farm, which sometimes I do, of course.)

    So, anyway, I woke up the other day and decided to extend the fast 24 hours to see what happens.

    I found that extending to a 40 hour fast was WAY EASIER than I thought it would be. I have found some research that’s shown that 40 hours is about limit before going into starvation mode.

    So, basically, I’m wanting to come up with a weekly cycle that makes sense. I was thinking “40hr fast / 32hr eat” … which is great if there was only 6 days in a week.. (and also causes me to question if it’s “okay to really have a 32hour eating window… or do I want to put a 16hr break in between)

    So, I’m looking for opinions on good cycle that would essentially give me weekends to not worry about fasting… and yes, even slip in another 40hr in the middle of the week. Here’s what I’m thinking:

    Friday – 00:00 – 11:59p FAST

    Saturday – 00:00a – 11:00a FAST
    - 11:00a – 19:00p EAT
    - Q: any harm in eating later here?
    - 19:00p – 11:59p FAST

    Sunday – 00:00a – 11:00a FAST
    - 11:00a – 19:00p EAT
    - 19:00p – 11:59p FAST

    Monday – 00:00a – 11:59p FAST

    Tuesday – 00:00a – 11:00a FAST
    - 11:00a – 19:00p EAT
    - 19:00p – 11:59p FAST

    Wednesday – 00:00a – 11:00a FAST
    - 11:00a – 19:00p EAT
    - 19:00p – 11:59p FAST

    Thursday – 00:00a – 11:00a FAST
    - 11:00a – 19:00p EAT
    - 19:00p – 11:59p FAST

    and back to:

    Friday – 00:00 – 11:59p FAST

    Hoping you’ll have some insights… or at least look at this and think “That looks like an awesome schedule” or “You’re Freakin’ crazy because___”


  3. I began doing IF just before this blog was written by Dr. Eades. I have progressed to eating one meal a day and I have made several observations on this technique. Firstly, science is given either too much credibility or it lacks patience. Patience must always be included to factoring in the truth.

    As a pre-diabetic, I include a low carb high fat menu to fasting. Along with that I take in calories during my fast. These calories are in the form of fat. I include coconut oil and heavy whipping cream to my morning coffee. This , I feel, enhances the ketogenic strengths of the fasting since fasting is ketogenic. Now here is my question, since fasting is ketogenic, why include the ruinous affects of carbohydrates to something that is ketogenic? Keep it all ketogenic is my rule. I do not define the time I eat by hunger anymore. I may be hungry but I do not eat just because of hunger pangs. I eat when I feel that I should, following my fast. When I do sit down to a meal that is a balance between nutrient dense, animal protein balanced with some good low carb vegetables and fat, I do it to set-up my next fast, not to end a fast. I want to be able to go for the next 24 hours in the comfort of ketosis.My blood glucose remains stable.

    As for weightloss, it depends all on me. The more active I am and the stricter I am with what I eat will indeed contribute to weightloss. Now, that being said, IF does not cause you to rinse a ton of poundage from your body. This is where patience must be factored in a scientific equasion. I lose about 12-20 pounds in a year. But it is also important to not assume anything without patience. There are times when it seems like , not only am I not losing, I seem to be gaining. I tend to do that. But by the end of 12 months, results will happen. If I do not allow the passage of time, I will not see these results.