Yang – Part 1 – What is Lost During a Diet or Fast?

There was an interesting study done back in the mid 1970’s. The study may not be possible today since there may now be ethical issues about starving people. We seem to have a fear of fasting that fails to take into account our human history of long fasts and famines.


The six subjects in the study were each given one of three different diets for ten days each. Over the course of the thirty days they ate either a ketogenic diet, a mix fat/carbohydrate diet, or they were fasted.
This is a pretty unique study since it provides the opportunity to see what effects fasting has vs other means of weight loss. Perhaps most interestingly is that they looked at what was lost during each of the three diets. Here’s the results of the losses from each in table form (with percentage of the total weight loss):
Diet/Intervention Weight Loss Water Loss Fat Loss Protein Loss
Ketogenic Diet 466 g/day 61.20% 35.00% 3.80%
Mixed diet 278 g/day 37.10% 59.50% 3.40%
Fasting 751 g/day 60.90% 32.40% 6.70%
Here is the same data in grams per day:
Weight Loss Water Loss Fat Loss Protein Loss
Ketogenic Diet 466.6 g/day 285.6 163.3 17.7
Mixed diet 277.9 g/day 103.1 165.4 9.4
Fasting 750.7 g/day 457.2 243.2 50.3

Ketogenic vs Mixed Diet

Once again the Ketogenic diet is shown to be more effective at weight loss than a mixed diet. However, the different is almost entirely made up of a much larger water loss on the keto diet than on the mixed diet. Looking at the grams per day of fat loss (the only thing that really matters in weight loss) the keto diet and the mixed diet are almost identical. Protein losses were equivalent on both the Keto and Mixed diets so there’s not much of an advantage to either. In the case of Keto vs Mixed it might just come down to which diet is easier to comply with and Keto wins that hands down for most people.

Fasting vs Ketogenic Diet

The results here show that a person can lose more weight fasting than they can even with either a ketogenic or a mixed diet. After all, they are eating nothing while fasting. Fasting produced almost three times the weight loss of the mixed diet. And when it comes to fat loss, fasting also wins hands down with a 1/3 greater amount of fat lost.

However, protein losses while fasting are almost twice those of the ketogenic diet on a percentage basis. The loss of 50g of Protein a day is almost two ounces of protein per day. That could be a significant amount for someone and is not a great preservation of Lean Body Mass.

The answer here may be found in the subjects themselves. They were six grossly obese males. The mean weight was 140 kg (308 lbs). They were great subjects for fasting since they had more than enough fat mass to support a ten day fast.

Fasting was slightly better about not having as much water loss as the Keto diet but Fasting was not as effective for weight loss as a percentage of weight lost.

What Does This Study Say About Fasting?

  1. Fasting produces the quickest weight loss of any of these three methods.
  2. Over 60% of the weight lost during a fast was water weight. This was the same for the Ketogenic diet. A mixed diet with carbohydrates is better at holding onto water. Much, it not all, of water weight is quickly regained after leaving the any diet.
  3. Fasting does not spare Protein as well as the Ketogenic diet. In fact, it is about twice as bad at preserving Protein.


Another Bone to Pick with Dr Fung

Another point I disagree with Dr. Fung is on the subject of Electrolytes. Dr Fung’s book, The Complete Guide to Fasting, leads many people to think that they don’t need electrolytes while doing Extended Fasting. They reach that conclusion from soundbites like the chapter heading:

Electrolytes Remain Stable (TCGtF, p 49)


Prolonged studies of fasting have shown no evidence of electrolyte imbalances…

This is led many to conclude that they don’t need to be concerned about electrolytes during extended fasting.

This is further exacerbated by Dr Fung being a clinician, IE, Dr Fung runs a weight loss clinic. He has thousands of patients and if he says that electrolytes are not needed then they are not needed… Or so the logic goes.

However, there are many others in the keto community who will tell you that they got into serious trouble by ignoring electrolytes. In particular, they had to end fasts due to electrolyte levels being way too low and some have ended up in the ER getting electrolytes via IV bags.

Looking at What Fung Actually Says

Fung’s book has different messages on electrolytes depending upon the fasting length.

p.48-49 During short-term fasts, salt depletion is not a concern.

p. 49 During prolonged fasting (more than a week) the kidneys are able to reabsorb and retain most of the salt needed by the body. However, some salt supplementation may be required.

People seem to miss the second part (on Extended Fasting).

There very little guidance on supplementation in the book, but several examples are found in the book (p. 240):

If you experience dizziness during your fast, most likely, you’re becoming dehydrated. Preventing this requires both salt [ed: Sodium and Chloride are two electrolytes] and water.

The same advice is given for headaches on the same page.

Also (p 241):

Muscle Cramps
Low magnesium, which is particularly common in diabetics, can cause muscle cramps. You may take over-the-counter magnesium supplement.

Facts Keep Getting in the Way

I have a serious concern with Dr. Fung’s method when it comes to Extended Fasts and the evidence against needing electrolytes. On p 50, Dr. Fung has Figure 1.4 which states in the legend:

Figure 1.4 Electrolytes remain stable during extended fasting

The book shows charts for Chloride, Potassium and Sodium.

But what is missing from these charts? What is in the charts themselves? And, who is the subject of the charts?

The charts are from the Guiness Book record holder for longest extended fast, Angus Barbieri. I have written about Angus’ fast. His fast was medically covered in this study (Stewart, Features of a successful therapeutic fast of 382 days’ duration).

Angus was a big man

There are some significant things of note. Angus was 456 lbs at the start of his fast. To use his extreme situation as evidence that electrolyte supplements are not needed during an extended fast is sketchy at best since he had so much available substrate to draw from during his fast.

Missing Data?

Further, Dr Fung omits in his book Angus’ Magnesium (Mg) levels which were published in the study and did show him with low Mg levels for much of the fast. The Normal range is clearly marked and the points are below that line. This is the figure from the study itself.

As you can see Angus’ Magnesium levels did drop during his fast very quickly and were on the low range of normal for almost the entire fast.

Fung doubles down with the statement (p 228):

While monitoring the world-record-breaking 382 day fast, researchers measured the magnesium content within the cells, which remained firmly in the normal range.

Dr Fung does go on to note (p 229) something ignored by many:

Nevertheless, we often supplement patients with magnesium to be on the safe side.

Did Angus Get Supplements?

The study also clearly notes that Angus was given supplements for the entire duration of his fast:

During the 382 days of his fast, vitamin supplements were given daily as ‘Multivite’ (BDH), vitamin C and yeast for the first 10 months and as ‘Paladac’ (Parke Davis), for the last 3 months.

I am not sure if the formula for Multivite has changed between the mid 1960’s and today, but the current formula is:

As you can see, Angus was actually given Magnesium, Potassium, Calcium and Phosphorus during his fast in the form of a supplement. Not in high dosage but not ZERO either.

Did Angus Receive Other Electrolytes?

The most serious issue with respect to Dr Fung’s claims about Angus’ fast however, is the study indicates that Angus actually did receive additional electrolytes during the fast.

From Day 93 to Day 162 only, he [sic: Angus] was given potassium supplements (two effervescent potassium tablets BPC supplying 13 mEq daily) and from Day 345 to Day 355 only he was given sodium supplements (2.5 g sodium chloride daily).

Here’s the chart from Dr Fung’s book which clearly shows Angus’ Potassium levels dropping below normal to the point where he was given potassium supplements (day 93 in the study). They went up to normal after Angus was given the Mg supplements and even after he discontinued the supplements.


Angus Barbieri is an example where electrolyte supplementation was required which is the exact opposite of what Dr Fung says in his book. Angus Barbieri was not only given Potassium when his levels fell, he was also given Sodium Chloride for another portion of his fast. He also had a daily vitamin which contained these elements.

Angus Barbieri was medically monitored and tested during his extended fasts. The doctors could tell when to supplement and when it was unnecessary.

It is a serious mistake to use Angus Barbieri as evidence that electrolyte supplementation doesn’t need to be done in Extended Fasting. Fung’s book on this subject is sloppy and ignores the evidence in the study. It sends a mixed message in the practical advice section later in the book from what it sent in the earlier part of the book.


I Keep Running into Fung-damentalists

I am a huge fan of Dr. Jason Fung. You can see throughout this BLOG how Dr Fung’s video on Diabetes and Intermittent Fasting turned my life around. But I also keep running into people who misunderstand Dr Fung’s words in his book and lectures.

An Extended Fast is not Short Fast

One of the ways that people frequently misunderstand Dr Fung is to take what Fung said about Short Term Fasts (3-4 days) and make it apply to longer (Extended) fasts (5+ days).

The study Dr Fung quotes on this point was (Zauner, Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine).

With any study it is important to know at least a few things:

  • Who were the participants? Are they like me?
  • How long was the study for?
  • What type of study was it?
  • What special conditions were there for the study?

In the case of this study the participants were:

Eleven healthy, lean volunteers (7 women and 4 men) participated in the study.

The study only lasted four days.

The first measurement was made after an overnight fast [started at 2100 the previous day (day 1)]. Further measurements were undertaken 36 h (day 2), 60 h (day 3), and 84 h (day 4) after the beginning of starvation. All volunteers entered the metabolic unit at 0700.
So, quoting the study to say that it is applicable to an Extended Fast it not justified based on the study. And that is not what Dr Fung has said. And if someone specifically asked Fung if the study warrants drawing conclusions about metabolism on longer fasts I seriously doubt he would say it does.
The study was done on an outpatient basis to mimic real life except the the study did limit sporting activity. Also, if you were told to limit yourself to only “necessary activities” would you do less? I’d skip doing the laundry for four days, etc.
The study was performed on an outpatient basis to keep subjects under normal living conditions. However, the subjects were instructed to perform only necessary physical activities (ie, to avoid sports).

What Did Fung Actually Write?

On several pages of Dr Fung’s book, he writes that Fasting does not lower metabolism. For instance:

In fact, metabolism revs up, not down, during fasting (The Complete Guide to Fasting, p 73).

And here:

And, studies show that after a four day fast, resting Energy Expenditure increased by 12-percent. Rather than slowing the metabolism, fasting revs it up. (TCGTF, p 49).

 As I have showed above the context of what Fung is writing is about a fast which lasted only four days. Further, Fung includes the data from the study in the chart (TCGTF, p 74).


Dr. Fung is talking about a short (four day fast). It is a mistake to extrapolate from a four day fast to a much longer fast.

The chart actually shows a decline in metabolism (the red line in the figure above) from day three to day 4 (45.3 to 44.3).

The reason that the body gets that energy burst at the start of any fast is explained in the study:

Our results indicate that an increase in serum norepinephrine concentration rather than a decrease in serum insulin concentration initiated by the decline in blood glucose concentration may be the primary initial signal of metabolic changes during early starvation.
This is a short term effect until ketone levels rise a few days into the fast and are able to provide energy at that point.
And to be fair to those who misunderstand him, Dr. Fung has not made this any easier due to the expansive language he uses. When he says “metabolism ramps up during fasting” in this context he means intermittent and short fasts. To take what Dr Fung says specifically about short term fasts and extrapolate it to Extended Fasts is not warranted either from the evidence from the study nor from Dr Fung’s own words.

Protein Sparing Modified Fast Calculator

I put together the previous formulas into one single webpage, the Protein Sparing Modified Fast Calculator. I’ve put my own current numbers into the calculator. Just hit the “Calculate” button to see my numbers. Feel free to try it out with your own numbers and see if it helps you figure out any of this. I don’t see the numbers you enter nor are they stored in any database. All of the calculations are done on your phone web browser or Internet browser (Firefox and Chrome works but Internet Explorer doesn’t).

If you find any errors, please let me know. I tried it with my own numbers and they make sense but I didn’t have a woman’s secret numbers to check.

Here’s a decent introduction to the Protein Sparing Modified Fast (PSMF). I only take exception to one point which is the question of how long you can do a PSMF. They say you can’t do it for an extended period of time. If you continually re-calculate your numbers you should be able to fine tune for maintenance levels. This calculator makes that re-calculation relatively easy. Here’s the results I got for my numbers.

Your Scale and Metabolism Numbers

Current Weight: 199.8 lbs
Goal Weight: 171.3 lbs
Lbs from Goal Weight at start: 28.5 lbs
Body Fat at start: 25.4%, 50.8 lbs
Lean Body Mass (LBM): 149.0 lbs
Basal Metabolic Rate (BMR): 1818.0 cal/day
Initial Total Daily Energy Expenditure (TDEE): 2500 cal/day
Initial Maximum Fat Loss on Protein Sparing Modified Fast: 0.45 lbs of body fat per day


Protein Sparing Modified Fast (PSMF) Dietary Macros (per day)

It is very important on the PSMF that you eat at least the macros listed here. If you go below these numbers you risk lowering your metabolism and you actually can’t lose body fat any faster. Attempting to be just above the numbers is OK.

Protein: 119.2 g (476.8 cals)
Carbs: 20 g (80 cals)
Fat: 40.9 g (367.7 cals)
Your total Dietary Calories are 924.4 cals for maximum fat loss.

If you consume 216 g (1943 calories) of fat you will stay at your current weight.At your goal weight you will be able to consume 119.2 grams of Protein, 20 grams of Carbs, and 176.3 grams of Fat.


Can You Fast?

One important question to ask when considering extended fasting is whether or not you have sufficient body fat to fast.

You currently use 2500 cal/day. You have 1575 calories per day available from your body fat for maintenance. You have less calories available from body fat than your daily requirements and may not be able to fast. If you fast, your body may drop your base metabolism, energy expenditures or may consume protein stores. You will be -924 calories short per day

The thermic effect of food contributes somewhere from 5-20% of your current TDEE number so if you are fasting that can reduce your TDEE. Reducing your TDEE by 10% would result in you using 2250 calories per day. Calculating in a 10% Thermic Effect of food still leaves you in a caloric deficit during fasting. The Protein Sparing Modified fast solves this issue by providing the calories needed for the deficit.

How Much Muscle Can You Gain?

The Maximum Lean Body Mass that you can carry on your frame is 186.5 lbs at your goal of: 15.0% Body Fat. That would be a weight of 214.5 lbs.


Use this information at your own risk and with the advice of your medical professional. We are not doctors nor do we pretend to be one on the Internet. We do not take responsibility for errors in these calculations. We do not guarantee that these numbers will work for people at the extremes of the ranges. If you discover an error in calculation, please let us know through email: keto at land-boards dot com.

Chia Seeds

I referred to Chia Seeds in another BLOG post as part of my refeeding strategy for ending extended fasts.

Chia Seeds are one of those SuperFoods which should be a part of our diet. They provide a lot of fiber and very few calories. One ounce (about 2 tablespoons) contains 139 calories, 4 grams of protein, 9 grams fat, 12 grams carbohydrates and 11 grams of fiber, plus vitamins and minerals.

For Low Carb folks the 12 grams of carbohydrates are before subtracting fiber so the net carbs are 1-2.

To use them I soak the seeds in water (1/4 cup seeds to 1 cup liquid) until they take on a chewy texture reminiscent of tapioca pudding, about 20 minutes. Soaked chia seeds can be refrigerated for up to 5 days, so you can make a big batch at the start of the week.

I eat them one day before ending a longer (more than 7 day) fast. I also eat them three hours before refeeding. I usually eat them with a dill pickle which acts as a Sodium bomb.


Electrolytes are not Optional During a Fast (KetoGains)

One things I have struggled with on extended fasts is getting the formula right for electrolytes. There’s a variety of advice on what to do about electrolytes during a long fast varying from next to nothing (the “tough it out” mentality) to very specific minimums.

KetoGains has the following recommendations for electrolytes:

That is probably the best listing I have found in one place of what to take and how much to take.

Franky I think I failed to go past 25 days in my last extended fast due to not keeping control of my electrolytes so I’ve got a particular interest in getting this right. I really haven’t paid much attention to electrolytes in the past. All I have done has been to add Morton Lite Salt to my coffee (a couple of shakes). Mortons Lite Salt is half Sodium Chloride and half Potassium Chloride.

The Nutrition Facts Label for Morton Lite Salt shows:

The problem with Morton Lite Salt is that it is intended to be used to replace regular table salt and the manufacturer adds Iodine. Each 1/4 tsp has 40% of the RDA for Iodine. Too much Iodine can be a bad thing. 3/4 tsp would exceed the daily RDA for Iodine and only provide 36% of the Sodium and 30% of the Potassium.  My conclusion is that the Morton Lite Salt is a good thing to add as a shake or two into coffee since it gets both Sodium and Potassium over a few hours or a day, but is insufficient for daily needs during extended fasting. So what to do for electrolytes during fasting?


For Sodium, this can easily be solved by using either Sea Salt or Pink Himalayan Salt. These salts do not contain Iodine. Morton Fine Sea Salt costs $2.24 for a 17.6 oz (500g) container.

Here is the nutrition label for the Morton Sea Salt.

To meet the 5000 mg minimum listed on the Ketogains electrolyte slide would be 10 servings of 1/4 tsp. The cost per day is ($2.24 for 36 servings or 6c per day).

Sodium: Use 2-1/2 tsp of Morton Sea Salt


Where should Potassium come from? The KetoGains Electrolyte slide shows Potassium from either Nu-Salt® or NoSalt.

Nu-Salt® contains 0.530 grams or 530 milligrams of Potassium per 1/6 tsp. (1 g) serving. So a tsp of Nu-Salt® would have 3180 mg of Potassium. A half tsp of Nu-Salt® would have 1590 mg of Potassium.

NoSalt is a similar product. It is available at WalMart for $5 for 11 ozs.

Here is the nutrition facts for NoSalt.

Presumably the .25 Serving size is 1/4 tsp? One tsp would be 2560 mg of potassium which is in the Ketogains range. That means that the container has about 60 days worth of NoSalt ($5.00/60 days is less than 10c per day).

Potassium: Use 1 tsp of NoSalt or NuSalt

Warning for Taking Dietary Postassium

Note some medications, such as ACE inhibitors for blood pressure interfere with Potassium. Read this warning. Consult your physician for specific information.


This is probably best done with a supplement.The Ketogains suggestion is to avoid Magnesium Oxide and use Magnesium Citrate instead. The Magnesium Citrate is available in smaller doses of 70 or 100 mg so more tablets are needed).

These are available from Walmart for $6 for a bottle of 100. Three capsules would get to the minimum 300 mg of the Ketogains numbers. That would be 18c per day.

Magnesium: Take 3 of 100 mg Magnesium Citrate tablets


  • Sodium: Use 2-1/2 tsp of Morton Sea Salt
  • Potassium: Use 1 tsp of NoSalt or NuSalt
  • Magnesium: Take 3 of 100 mg Magnesium Citrate tablets

These are numbers for fasting only. Less are required when eating since some of these come from food.


Biochemical Stages of Short and Long Fasts

Here’s a great paper on what happens during a short and a long fast.

The paper covers the daily feast/fast cycle of the regular American diet. It also covers what happens over a longer fast. One of the interesting charts relates to a longer fast:

The chart on the left is the Glucose level over a longer fast and the chart on the right is the Ketone Bodies chart. Per the charts the Blood Glucose falls faster than the Ketone Bodies can kick in. That could the reason that the third day of an extended fast is considered to be the toughest. This also explains why it is much easier to enter a fast being already in Ketosis because your Ketone levels are higher.


The Cori Cycle – Not a new kind of bicycle

I had an interesting response to intense exercise the other day. I was many days fasted and went to an introductory CrossFit class. I measured my blood sugar after I got home from the class and my blood sugar was around 80 points higher. Did some digging to try and find out why.

My first assumption was that the liver was dumping glycogen and that’s partly true. Turns out that the muscles store around 80% of our glycogen stores and the liver contains the rest. The muscles use the glycogen locally and they don’t dump glucose into the blood stream. All of the glucose does come from the liver which takes it out of stored glycogen. That would account for some of the rise. I usually see a ten point pop with some exercise like bike riding but not like that time. The CrossFit exercise was very hard compared to normal exercise.

Here’s where the the Cori Cycle comes into play. I was fasted during the exercise for more than 20 days. From the Wikipedia article:

The Cori cycle is a much more important source of substrate for gluconeogenesis than food. The contribution of Cori cycle lactate to overall glucose production increases with fasting duration. Specifically, after 12, 20, and 40 hours of fasting by human volunteers, the contribution of Cori cycle lactate to gluconeogenesis is 41%, 71%, and 92%, respectively.

This was a piece of data which I didn’t have before. This makes sense of the experience that I had with intense exercise. The muscles released a lot of lactate which at the end of the exercise gets converted in the liver through gluconeogenesis into glucose. Hence, the large pop in blood sugars.

Here is a great discussion of exercise and the Type 2 Diabetic with Dr Finney.


Tapped Out at 25 Days

I made it 25 days on my Water Only Fast. Ended yesterday. I miss fasting already. Felt better while fasting than I do on food. Ended with Chia Seeds and a pickle. The Chia Seeds act like a slowly moving cork through the system which is good after a long fast.

Thinking about doing Chia Seeds once a day on my next fast. Won’t technically be a water fast, but I like the idea of keeping some fiber moving through my system. I am just a few lbs over my goal weight so I am not in all that much of a hurry.

Weight loss was 24 lbs. Should hang onto a lot of it since I really kept up on salt.

Can’t wait to do my next Extended Fast. Maybe after the Keto meetup this weekend.

Tomorrow is my third intro class to CrossFit then I can join the regular people in torturing myself. I know that this will be much harder than Keto and Intermittent Fasting. And I will definitely keep up the Intermittent Fasting and Keto. Never going to give up the gains I have made with Keto + IF.