Intermittent fasting, measured heart rate. More calories effective or not?

[SgtAnderson]

Hello,

People, I follow intermittent fasting.

This means a period of 16-20 hours no food and eat within 4 tot 8 hours. 
This does not need to be within 1 day.  You can fast for 20 hours and eat for 8 hours if u wish.

Anyway,

When I start eating at 14:00 and stop eating at 18:00.
I go to the gym between 12:00 and 14:00.
Now I notice I burn like 250 kcal per hour while fasted and If I eat some sugars before the training I burn like 350 kcal an hour with exact the same workout. (Strenght)

So now I wonder, deos your body actually always burn higher calories on a higher heart rate or is this relative? 
Do I burn the same amount of calories or do I actually burn a lot more when going to do training while not fasted?!

Would like to hear others opinion on this.

Thanks in advance.

[Dominique]

Yes, generally speaking you would burn more performing the same activity at a higher HR level than at a lower one, a bit like the same car would consume more gasoline at 80 mph than at 60 mph.

However, I would be surprised if you would burn less while fasted than when performing the same activity while not fasted. Do you perform the same lifts, with the same weights, for the same number of sets, reps per set and rest between sets?

What I would believe is you would have less energy with depleted glycogen stores, which would translate into lousier performance. This in itself would make an argument for not training while fasted, regardless of what Fitbit says about HR and calories burned. After all, the main purpose of strength training is to gain strength, not to burn calories or improve your cardio fitness (these would come as fringe benefits).

[SgtAnderson]

Thanks for your reply.

When u compare a car. Driving at 80 mph to a car at 60mph it will reach the end goal much faster.

So If higher heart rate would 'always' imply more calories burned then I would say I do burn more calories after eating.

The idea of Intermittent fasting is less insuline spikes, better controll of blood sugar.

Also I have been in a calorie deficit for a few weeks now witha 1 day per week 500 calories above maintenance(refeed). So my performance is not 100%, but does not really impact me yet.

Three times a week I perform the same lifts, with the same reps and the same rest in between sets.

Few days ago I started my eating window before I go do lifting, just to be sure I burn the most calories and be able to eat as much as possible.

But still I remain curious about the science behind it.

[divedragon]

I work out in a fasted state and do so for what fasting does to help you with your muscle growth.  When you fast, you alter your hormonal balance and the longer you fast, the greater is the alteration.  The biggest benefit is that your growth hormone production can increase as much 3000% - no I didn't put too many zero's in there.  Additionally, you produce more stem cells.  Just these two in combination would tell you that it's a good way to bulk up, but this isn't all.  While blood cells that are old are actually consumed as is a lot of other dead and dying cells in a process known as autophagy.  This leaves room for the stem cells combined with growth hormone to build back new cells including muscle tissue you damage during weight training.

The concept that without glucose you muscle can't do as much work is proving not to be true.  In fact, muscle tissue seems to prefer the energy it gets from ketones over that of glucose.  You may find that the further you are into fasting, the more energy you have.  Six months ago, I couldn't do 10 pushups.  Now I do at least 4 sets of 15 every day and I ONLY exercise fasted. 

Finally, several studies have shown that just fasting alone - even in the absence of weight loss, increases the lean to fat ratio.  Exercise only adds to that - which is why IF is being adopted by the bodybuilding community.

Fasting does lower you pluse.  During my most recent 7 day fast, my resting heartrate dropped to 54.  After re-feeding it came up to 62 which is normal for me.

[Dominique]

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@divedragon wrote:

The concept that without glucose you muscle can't do as much work is proving not to be true.  In fact, muscle tissue seems to prefer the energy it gets from ketones over that of glucose.

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Now, I would really like to see authoritative sources backing these claims.

[SgtAnderson]

My friend, thanks for your reply.

But you just stated the basic information of intermittent fasting.
You would imagine I know this(since why else would I do IF), but summing it up has nothing to do with my question. 🙂

The only thing I'm interested in is If I burn more calories while training fasted or non fasted or if it's equal. 

[divedragon]

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@Dominique wrote:

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@divedragon wrote:

The concept that without glucose you muscle can't do as much work is proving not to be true.  In fact, muscle tissue seems to prefer the energy it gets from ketones over that of glucose.

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Now, I would really like to see authoritative sources backing these claims.

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Sure, don't blame you at all for this.  Here a just a couple, but there are many studies that report these findings. The following is taken from this review of studies discuss this and outright state they are preferred by the heart.  For clarification, PF is prolonged fasting  or > 24 hours:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946160/

In rats, the combination of alternate day fasting and treadmill exercise resulted in greater maintenance of muscle mass than did IF or exercise alone (Sakamoto and Grunewald, 1987). Interestingly, when rats were maintained for 10 weeks on a PF diet in which they fasted 3 consecutive days each week, they were less prone to hypoglycemia during 2 hours of strenuous swimming exercise as a result of their accumulation of larger intramuscular stores of glycogen and triglycerides

And at this website: http://users.humboldt.edu/rpaselk/C438.S07/C438Notes/C438nLec36.htm

The ketone bodies are water soluble and are transported across the inner mitochondrial membrane as well as across the blood-brain barrier and cell membranes. Thus they can be used as a fuel source by a variety of tissues including the CNS. They are preferred substrates for aerobic muscle and heart, thus sparing glucose when they are available.

[divedragon]

My apologies that I didn't answer your question more directly.  I'll try to do better here.  The short answer is possibly more and here is why.

The amount of energy you expend during exercise, assuming your effort is equal, will be the same in fasted or non-fasted state.  There are, as I'm sure you know, 2 aspects to energy consumption: 1) Your basic metabolic rate + 2) Your exercise/activity energy burn = Totaly energy expended.  Evidence shows that during fasting, BMR will actually increase once in full ketosis.  With this in mind, if your BMR is higher and then you expend energy at an equal rate as non-fasted, your total energy expended will be slightly higher.  This rate depends on a lot of variables that include length of time in fasting (longer is better up to a point), fat reserves, hormonal balance, hydration level and many other factors, but the potential is certainly there to burn more calories by combining fasting with exercise.

[jbz16]

You all seem to be fairly knowledgable regarding IF, I've been following keto-diet and exercising very regularly for 2 weeks (in ketosis). Just going into my IF phases of my plan- how long should a normal IF phase last for maximum fat burn results? Are we looking at a couple of days? Or a couple of weeks? What has the least risk of being unhealthy for your body or repercussions of other problems developing for that amount of extended time?

What I have been doing is using my IF days on days where I don't have sports or training - then on the days where I will be expelling more energy for extended times, I go back into my regular meals throughout the day. I seem to have hit a weight loss plateau?

[divedragon]

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@jbz16 wrote:
You all seem to be fairly knowledgable regarding IF, I've been following keto-diet and exercising very regularly for 2 weeks (in ketosis). Just going into my IF phases of my plan- how long should a normal IF phase last for maximum fat burn results? Are we looking at a couple of days? Or a couple of weeks? What has the least risk of being unhealthy for your body or repercussions of other problems developing for that amount of extended time?

What I have been doing is using my IF days on days where I don't have sports or training - then on the days where I will be expelling more energy for extended times, I go back into my regular meals throughout the day. I seem to have hit a weight loss plateau?

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@jbz16At the risk of being quite verbose, I'll try to answer you questions as best I can.  Let me start with the Ketosis side of things.  Just because you are in a state of ketosis, doesn't mean you are burning stored fat.  If you've hit a plateau and are still solidly in ketosis, you are probably consuming too many calories.  You are remaining in the state because your body is breaking down dietary fat rather than stored fat. 

I don't do IF phases.  IF is a way of life for me and I fast every M-W-F.  If your desire is to loose fat and you've currently stalled, one way to kick start your weight loss again is to do a 7 day fast.  When I say that, I mean water, coffee, tea only for 7 days straight.  Drink lots of water during the fast.

As to exercise, the idea that you shouldn't exercise on a fasting day is derived from the false notion that without food we become weaker and therefor can't perform at the optimum level.  Qutie the opposite is true.  For maximum fat loss, exercise on fasting days and preferrably towards the end of your fast.  Why?  Fasting causes an increase in growth hormone and stem cell production.  Energy is derived from ketone bodies which more efficently convert ATP to ADP and back.  Growth hormones have been shown to increase as much as 3000 percent during fasting.  This can supercharge your muscle growth over exercise during  feeding states.  The longer the fast (in terms of hours per fast) the faster the results.  Exercising during fasting states will also ramp up your stored fat burn as your body will need to pull from these stores to fuel your workouts and recovery.

The biggest benefits from fasting seem to happen at between 36 and 48 hours.  My 3 day/week schedule gives me 3 - 36 hour fast/week and I workout in the evening of those fasted days.  6 months ago I couldn't do 10 pushups.  Now I do 20 at a time, 4 times a day and I'm 58.  Working up to more.

Some other benefits of fasting include brain neuron production, autophagy (removal of dead and dying cells throughour the body), reduction in total body inflamation, reduction in LDL with an increase in LDL particle size, increase in HDL, reduction in blood pressure, reduction in resting heart rate and improvement in bowel function.  The University of Southern California Center for Longevity recommends fasting to prevent age related cognitive desease.  There may be evidence that fasting can even help or prevent cancer as cancer cells can ONLY survive on glucose (your keto diet helps here too).  Combined with the autophagy that will chew them up and spit them out when they weaken and. you see where I'm going.

I consider making fasting a regular part of your diet.  Even if 2 days a week.  Consider a 5-7 day fast once a quarter on top of that.  Exercise in the fasted state and eat a lot of high quality, grown above ground vegies with your diet.   Let me know if I can be of any more assistance and good luck breaking your plateau.

[A_Lurker]

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@divedragon wrote:

I don't do IF phases.  IF is a way of life for me and I fast every M-W-F.  If your desire is to loose fat and you've currently stalled, one way to kick start your weight loss again is to do a 7 day fast.  When I say that, I mean water, coffee, tea only for 7 days straight.

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I don't want to open the debate on IF as a lifestyle and/or a way to lose weight, however, you should point out that most references on fasting suggest that you don't jump into a 7-day fast for the first time without at minimum discussing it with a doctor.

http://www.allaboutfasting.com/who-can-fast.html