Dieting vs. Fasting - Research

Hi Dr. Darden -

Happy New Year and hope your holidays were great.

Question: a couple of friends have jumped on the Intermittent Fasting bandwagon and asked me to read a book by Dr. Jason Fung, MD, watch a couple of movies on the topic. One thing Dr. Fung brings up: with dieting, your metabolism is lowered for months or years if you lower your caloric intake. Studies, research, et al, are cited. With IF, and in some examples IF combined with a higher fat diet, metabolism remains the same or increases per Fung’s references, the MDs in the movies, etc.

Any thoughts on this?


Anybody can cite studies to prove pretty much anything.
So that in itself is meaningless.
To lose weight you have to create a caloric deficit , irrespective of the diet used (including Dr Fung’s).
Doing so in isolation will lower the basal metabolic rate. A major reason for this is that some of the weight lost will be muscle tissue.
That is one of the key reasons why Dr Darden has promoted progressive high intensity weight training for so many years.
Not only do his clients not lose muscle on a diet , but they actually gain muscle , thereby boosting ones metabolic rate.
There are of course other things to take into consideration, but in simple terms the best way to lose fat is to create a caloric deficit , and to progressively lift weights.



I tried IF for a while. I became dehydrated. I thought I was drinking enough water. My kidney function decreased to disease levels.
I know this because I get bloodwork a few times a year. My doctor sent me to a nephrologist.

I had to make a few changes. Limit caffeine. I stopped red meat. I went back to drinking lots of water along the lines of what Dr.Darden recommends.
My kidney function is back to normal now.

I don’t care what any possitive research says. No way would I use IF again.

The key to any diet is stick to something that is sustainable.

Did you ever notice people with low body fat that are ripped? Who say that is because they IF.

Read what Dr.Darden says about genetics.


I tried IF a couple years ago, never lost a pound and was hungry all the time…when I did eat I ate everything in site…not for me

Both the brain and muscles preferably use carbohydrates as the primary fuel. A high carbohydrate diet with calorie control (or restriction) works. Why interfere with the normal bodily functions? I rest my case. Eat your breakfast!

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Thanks for this post!

Understood, but, that wasn’t the question.

The question was on lowering your calories and the long term affect on your metabolism based on the results of multiple, fairly large studies and research.

I think if you take IF out of the equation. Lower/keep your calories to where you are fairly lean for you it should be better for your overall health.

As long as you lift weights in a progressive way and keep away from extreme/fad diets , then any reduction of metabolic rate will be small and short lived.


Mark/Dips - That is still not what is being asked in my post to Dr. Darden. The science cited by Fung (and I also believe work with his own patients) and others stated:

  1. Extended caloric reduction via a “diet” = slower metabolism.
  2. Intermittent Fasting = No reduction in one’s metabolism, better insulin sensitivity, more optimized periods of autophagy + growth hormone + glucagon.

Dr. Darden does advocate a low caloric intake in his books via 3x meals + 2x snacks/day, superhydration and HIT – with lots of emphasis on negative training. The reduced calories is for periods of six weeks.

“then any reduction of metabolic rate will be small and short lived.”

According to multiple sources cited by the authors, videos, etc., I’m referring to, this is not correct. I can try to find their references and post them. Would be interested in your references or work in this area?

I told you what happened to me with IF. When my kidneys declined so did my metabolism. Science and a Doctor figured out what happend to me.

Studies can be a crap shoot. I would look for how long the study was and who sponsored it.

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Sorry dips, I didn’t actually understand why you simply haven’t up your water intake, no matter which diet style you incorporated at that time?

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I am not a scientist.
I have trained people and given them diets ,I have competed in bodybuilding numerous times and have helped others with their prep.
At no stage has there ever been a problem noticed with anyones metabolic rate.
In fact when I was at my leannest ever in 2012 ,I increased calories , got even leaner and gained 2 pounds for my next contest (without any "assistance ").
In regards Dr Fung’s claims , I consider them complete BS.
His views on nutrition are certainty not mainstream (which in itself does not make them good or bad,. But it is important to mention that) and are carefully selected and often taken “out of context” to “prove his points”
I don’t have any issue with IF , but I do have with many of the unproven claims of superiority of it. by some of its supporters.
These represent my own views from 38 years of being involved with exercise and nutrition.



I was drinking about 48 oz. a day.

I used to be a late night eater, but it started to get to my stomach. So, I don’t eat 4-5 hours before bedtime which means I go about 12-13 hours a day ‘fasting’. Maybe even 14 hours on weekends. I did lose weight this way without trying. However, I also drink a lot of water throughout the day and still pack in enough calories during the day.

I was watching Joe Rogan who had Ronnie Coleman on recently. Ronnie said he used to wake up in middle of night to eat and go back to sleep during his competitive days. lol I cannot imagine.

dips, there’s your problem right there. 48 oz. is nothing. Even Dr. Darden would recommend a gallon of water a day.

Studies can say whatever they were designed to say.

According to this documentary, IF reduces metabolism as well.

Watch Beyond Weight Loss | Prime Video (

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I used to do that no food after dinner routine because heard that that food mostly turned to fat but I found after doing that I would wake up early and not get enough sleep. It seems my body type needs some carbohydrates before bed.

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Ok, but why haven’t you up that amount?
Sorry if I understood something wrong, english is not my first language…

Neither am I a scientist. I’ve read various books, papers, etc., and have been my leanest on a diet around 50% carbs, 30% protein, 20% fat. Also helped others while I was in the military get ready for team qualifcation, annual testing. Got in shape for some endurance events, did well. Did compete in a bb’ing contest once – mediocre genetics – so one and done.

Regarding Fung, I’d suggest calling them “clams” is a misrepresentation – if you haven’t read his references and work with his patients, then, I don’t understand how can dismiss them as BS.

Yet you note you’re not a scientist or MD (nor am I), but, said there has never been a problem with anyone’s metabolic rate. So assuming, you didn’t take bloodwork? Test factors that determine an individual’s metabolism before/after?

And Fung’s “views on nutrition” --he does encourage low carb, but, he also states in one of the books I read whole/complex carbs such as legumes are acceptable. But, he is very, very much against fructose and processed carbs – especially fructose because of its affect on the kidneys to include inflammation and other issues (he’s a nephrologist). Not mainstream, for sure, as it goes against the Standard American Diet.

If you haven’t read his books (have read three loaned me), watched his videos (also a couple of movies he’s in such as Fasting on Prime), etc., your statements appear to be misrepresenting Fung (and other MDs) regarding his information and recommendations.