Working out during Intermittent Fasting

[renee9605]

I have been on a 16:8 IF schedule, eating from 12pm-8pm. I usually work out after work, so around 4:30pm, but I'm thinking of trying to switch to a schedule that would allow me to work out in a fasted state. But that would mean exercise at 5:30am. It's a pretty vigorous cardio-kickboxing workout, where I average 375 calories in 30 minutes. My concern is this: is 6 hours post-workout too long to go before eating? This is, of course, on the assumption that I'm not feeling dizzy, fatigued, nauseous, etc. My primary goal is fat burning. Thanks in advance!

[bikerhiker]

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@renee9605 wrote:

I have been on a 16:8 IF schedule, eating from 12pm-8pm. I usually work out after work, so around 4:30pm, but I'm thinking of trying to switch to a schedule that would allow me to work out in a fasted state. But that would mean exercise at 5:30am. It's a pretty vigorous cardio-kickboxing workout, where I average 375 calories in 30 minutes. My concern is this: is 6 hours post-workout too long to go before eating? This is, of course, on the assumption that I'm not feeling dizzy, fatigued, nauseous, etc. My primary goal is fat burning. Thanks in advance!

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Before I discuss your situation, I like to lay out the frame work on fat burning and the 4 facts.

Fact 1: 1 pound of fat = 3500 calories

Fact 2: 1 pound of lean muscle mass = 600 calories

Fact 3: When a person is in a higher body fat %, which is classified as obese in the BMI range, this person will burn fat while engaging in a high caloric deficit.

Fact 4: When a person is in a lower body fat%m which is classified as lean and average in the BMI range, this person will lose muscle mass while engaging in the same high caloric deficit as Fact 3.

So let's bring this into some perspective.

Consider a person who is engaging a 500 calorie deficit/day for 7 days, you will get 2 different outcomes depending on your body fat % during the time of the caloric deficit.  One outcome would be that with a 500 calorie deficit/day, in 7 days you will lose 1 lb of fat (500x7 =3500 calories).

However, the same person who has a lower body fat % and engages the same 500 calorie deficit / day will lose roughly 6 lb of lean muscle mass after day 7 (3500 calories / 600 calories).

For example, anyone who is obese can engage in a high extreme caloric deficit like what you see with the 1000 calories challenge or even the 600 calories challenge.  That 600 calories is the average calories the Venezuelans get per day.  Fat loss will occur, because when the body has so much body fat, it can spare some of that to cover the caloric deficit from meals and the hard workout.  But eventually your weight will plateau because your body will protect the body fat for survival purpose.  So the next phase of losing body fat is to do body recomposition to focus on building more lean muscle mass and increasing caloric consumption to be able to promote protein synthesis for more muscle growth.  So what you should be asking is; how could I modify my diet to compensate for my current body fat% and activity level so I can burn fat, while increase lean muscle mass.  If you didn't ask this question, then I would highly suspect that what you are doing now is not burning fat, but rather losing muscle mass and bone density and what the scale reflects to you is that loss; not body fat.

To promote loss of body fat, you need to tailor your calorie consumption based on

1, current body fat% (you need to measure it)

2, activity level (you need to measure those to)

Then calculate your true TDEE and macros as reflected in the now and make sure they are correct to your body fat% and activity level as the leaner you go, the more precise they have to be as you want muscle growth and not gaining more fat.  Timing your meals won't work at all.  It doesn't really matter when you eat your meals.  If you need to consume 3500 calories; whether you skip breakfast and eat only lunch and maybe dinner does not really matter, because you eventually end up with 3500 calories.  The first law of thermodynamics states that energy can neither be created nor destroyed; it can only be transformed from one form to another meaning food into fuel for the body. 

What intermittent fasting can create is the potential of lost of lean muscle mass, because when the body is starved for fuel, it doesn't chose where it gets its energy, especially when the body fat% is low enough that it is in survival mode.  In survival mode, It gets its emergency fuel from where it is the easiest to burn-- glucose and that comes from your lean muscle mass by the process called gluconeogenesis. 

Do you know what's the most effective fasting the natural way that's guaranteed to work day after day?  It is called sleep.  Did you know that the difference between sleeping for 5.5hrs as opposed to sleeping for 8.5hrs?  If you sleep only for 5.5hrs, your fat loss can decline by 55 percent!  Why worry when you should eat and skip meals when you can get the best bang for the buck just to have a deeper longer sleep.  Here's the research to this study from US National Library of Medicine.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2951287/

I think your concern right now should be -- what am I burning while doing all these workouts and intermittent fasting?  Am I burning more body fat, or am I losing more lean muscle mass and bone mass?

[Dominique]

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@renee9605 wrote:

I'm thinking of trying to switch to a schedule that would allow me to work out in a fasted state.

[...}

My primary goal is fat burning.

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If you’re primarily interested in losing fat, the most important is to make sure you’re in an overall caloric deficit. Nutrient timing (how you spread your intake across the day) will only play a minor role. And working out in a "fasted state" won’t cause you to burn more fat. 

[Baltoscott · Accepted solution]

Hi @renee9605 -- I work out in the mornings and usually have something to eat both before and after on the theory that I want carbs available to fuel the workout, and I want protein available to rebuild and repair the muscle breakdown I create. 

But there are researchers looking into working out in a fasted state and I just read an interesting article in the NYT about a study suggesting that you may be able to increase your daily negative energy balance (assuming you are trying to lose weight) by skipping breakfast before working out. Here is a link to the study itself.

Since you already seem to be happy on a 16:8 IF schedule (not for me, thanks!), why not give it a try for a couple of months?  If you don't like it, it's easy enough to go back to your current schedule.  And one BIG plus about morning workouts is that if you have to miss one for some reason, you still have a lot of day left to make it up.