Intermittent Fasting Part 2 – Fast-5 Diet

Ok folks, my approach to this post is the same as in part 1– I’ll present the facts from the book Fast-5, written by Bert W. Herring M.D.

However, I will assume that you now understand the basics.

This book is slightly different because the message is targeted more toward “normal people”, and less toward people who’re into fitness and working out. There’s more of an emphasis on the diet and the process of fasting in this book, and it promotes a feeding gap 5 hours long from 5pm to 10pm followed by a fasting period of 19 hours until 5 pm again the next day.

(I have tried this approach of 5/19 vs the leangains approach of 8/16 and have noticed no major differences. However I find it easier to eat two really large meals with the leangains one because 5 hours isn’t quite enough time for me to get hungry again – I might as well just eat one large meal in that case.)


Main Points from Fast-5


Once you are in a fasted state, and your body is using energy from storage (fat) rather than from fresh glucose absorbed from digesting food, it’s easier to keep this steady state than to flip back and forth from fat to glucose and back again. Changing back and forth causes fluctuations in the levels of hunger-related hormones such as insulin, ghrelin, leptin etc.

When you’re adjusting to the diet, your body is in the process of changing its primary energy source from glucose absorbed from food to ketones and fatty acids released from fat cells. As your glucose storage becomes depleted, the fat burning process starts, making it easier for you as your body adapts.

The sensation of hunger may be caused more by the changing levels of these hormones than from the lack of food in the stomach or gut. This is hormonal hunger.

Limbic Hunger

Have you ever wondered why you can’t seem to stop once you start eating for example, ice cream or potato chips?

The reason you don’t want to just eat one potato chip is because of LIMBIC HUNGER. By eating the first chip you trigger more appetite due to primitive limbic signals that tell our brains we should eat as possible while the food is available, plus it gives you an insulin spike. This increases your sensation of hunger, and will spur you on to eat the whole bag of chips unless you have the willpower not to.

(Basically limbic hunger is there since we were cavemen and it was a smart idea to binge-eat a lot because food was scarce and there might be a long time until we could get more of it.

This is the explanation for why it’s easier to not eat at all, than it is to eat just a little. It’s a bad idea to snack or eat a little because it raises your insulin levels and stokes your limbic hunger. For me, the effect of limbic hunger is very strong because my insulin sensitivity is low, since I know this from making the mistake lots of times I know from experience that it’s far easier to just abstain from eating in the first place)

Somatic Hunger

This is the sensation of discomfort in the gut that is often referred to as hunger or hunger pangs. Whenever the stomach is empty, hormones get sent out to inform the brain.


Is breakfast the most important meal of the day?

This slogan was brought to you by the same system that resulted in making 65% of the American people overweight: it helped selling lots of breakfast cereal and toaster pastries.

Sugar during the Fasted Period?

He claims that: “Aspartame may be better than sucralose because sucralose may have unpleasant side effects on your gut when it is the only thing you’re consuming”

However later remarking: “Don’t take the first bite until it is time for “break-fast”, and make sure you’re not accidentally breaking your fast with an unrecognized calorie creep such as milk, cream, sugar in your coffee, mints or chewing gums, before 5 pm.”

(I’d advise you to avoid sugar as much as you can)

Don’t break the fast with Alcohol

By drinking alcohol you will reduce the liver’s ability to metabolize. This can lead to a major drop in blood sugar which can feel bad as well as be unsafe for certain people. The research is inconclusive, but it’s better to be on the safe side.

(I have broken fasts of about 16-20 hours by drinking 2-3 times. It actually felt pleasant and I had a great time. But I doubt it was particularly healthy, especially when I went on a drunken binge)


When you’ve fasted on a daily basis for about two weeks, your glycogen storage should be depleted. By now your body will be fully activated to use its “fat-handling” enzymes. This will make your body better at metabolizing fat, which is only logical since that’s all you have been giving it to get energy from for 19 hours every day.

Your breath may smell bad by now. This is a sign that your body has begun the process of ketosis and is now running on ketones.


If you keep switching it up by not having a consistent schedule, it will make it harder for you due to your body not being able to hormonally adjust. Therefore you should carefully tailor your schedule in regards to what times work best for you every day.

(This is something I’ve frequently experienced and in my opinion there are huge benefits to having a steady schedule for eating and sleeping. This can be quite a challenge when you reside in a loud or harsh environment.

I know that this is true for me through first-hand experience, but what I wondering about is how this consistency principle aligns with Brad Pilon’s style of doing IF for 24h  1-2 days a week. I wonder if the body is able to adjust to it as effectively as doing a leangains or Fast-5 style of IF every day. If anyone can give me their opinion on this, then I’d be grateful.)

Fasting & Muscle retention

Here’s his take on this:

My doctor/friend/trainer etc. says that fasting burns muscle, is that true?

1.       Prolonged, multi-day fasting will if necessary, use muscle protein to make glucose for the liver and brain, since your body cannot make glucose from fat. The daily meal you have with the fast-5 plan makes protein and glucose available for use and storage, so it does not have to use protein from muscle. That is why it’s important to keep a balanced diet that includes a generous portion of protein and to engage in some light exercise. The dietary protein intake and the use of muscles for exercise work together to protect muscles mass.

2.       “If you do lose muscle in the weight-loss process despite protein intake and exercise, it’s going to be at most about one-twentieth of the weight that you lose, or 5 %. Exercise can restore that muscle.”

(So basically, don’t do prolonged periods of fasting (well above 24h) and lift weights.)

Insulin & Leptin

We all know how important insulin is in this process, but let’s take a closer look at leptin.

Leptin has a few things in common with insulin. They are both hormones used to suppress fat breakdown the fat cells and they both inhibit your body’s ability to release fat in the form of fatty acids (ketones) into the bloodstream as a way of providing energy to the body.

Another thing leptin and insulin have in common is that their levels become elevated when you have eaten recently.

Insulin acts right away and you get an almost immediate spike as result of eating. Insulin signals to your body that there is energy available for it to absorb right now.

Leptin on the other hand is slightly more long-term, reporting the recent trend of whether your body has been supplied with enough energy in the last day or two. When you eat, both insulin and leptin send the message to your body telling it to store fuel (fat) and not to release it.

(We dealt with insulin in part 1, you should know this, and therefore I won’t get into more depth. Here’s a good article on leptin if you want to read more.)

Obese people are commonly insulin resistant, resulting in their bodies having a slower response to insulin. This yields them higher peaks in insulin levels than non-obese people. Obese people therefore get more sudden hunger-pangs – hormonal hunger. Obese people also have higher leptin levels due to having more fat – and leptin is produced by fat cells.

Eating 3+ Meals per Day

Since it takes your body a couple of hours to digest food, and the blood glucose levels (insulin levels) needs a few hours until it drops back to the baseline, eating three or more meals a day will result in your body maintaining a steady flow of glucose into the bloodstream.

This keeps your levels of insulin and leptin to be high constantly and remaining active. Therefore you won’t be burning any body fat.

Going in between Meals

By eating fewer meals and going longer in between them it will cause insulin and leptin levels to fall down to a baseline level in which your body can burn fat.

Fat cells are not able to switch back and forth from absorbing glucose to releasing fats instantly like hitting a light switch. It takes time.

ATL – Adipose Triglyceride Lipase

Apart from insulin and leptin, there’s a third important component as to why fasting works – adipose triglyceride lipase.

There have been studies that indicated that fasting leads to an increase of activity/amount of ATL-enzymes inside fat cells, making it quicker for the body break down the triglyceride into a fatty acid so that it can be transported into the bloodstream and used as energy through ketosis.

(This is pretty straight-forward. If the body has to remain in a fasted state, of course it will adapt to it as efficiently as possible and make it easier for itself by increasing its ability to run off of fatty acids as opposed to glucose, when no glucose is supplied.)

Here’s part 3.


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  1. missytree says

    I started IF about two months ago. Love it. It’s easy, and I feel great! Excellent articles too, thanks for sharing.

    • Hey,

      I agree. It is way simple, if there ever was a magic pill to mental clarity and lower body fat that would be it. :)

      Thanks a lot!

  2. Nice.

    Liked this one better than part 1, easier to read / better layout. Your writing is improving my friend.

    Didn’t know the distinctions of limbic hunger & somatic hunger either, you learn something every day :)

    I started IFing everyday 2 weeks ago btw. I am doing a feeding gap of 7 hours and it seems to be working well for me, the first week was a bitch tho!

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