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Posted by on Feb 21, 2014 in Nutrition, Chewing It Over | 0 comments

Fasting, Weight loss and Muscle Maintenance

Fasting, Weight loss and Muscle Maintenance

A subject that has been creating some buzz among the health and fitness community lately, is the concept of fasting or intermittent fasting. Yes, I know. Your weight loss coach is gonna spank you, but let’s geek out for a bit. 

Does it induce the Starvation Mode? 

The earliest research demonstrating lowered metabolic rate in response to fasting dated back to 1987 [1]. Six male subjects experienced an 8% drop in metabolism in response to a 3 day (72 hrs) fast…not bad actually.

Other studies show metabolic rate is not impacted until 3-4 days (72-96) hours have passed; and to confound the situation even more, two recent studies have proved that metabolic rate is actually increased in short-term fasting due to increase in plasma norepinephrine [2] & [3].caveman

And of course, why shouldn’t it? This makes perfect sense from an evolutionary perspective. Epinephrine and norepinephrine are the fight-or-flight hormones that kick in to sharpen the mind and provide energy to seek food, hunt for prey if necessary, and increase survival. However, after several days of not eating, this tactic would offer no benefit and does more harm than good; so the next advantageous survival adaptation is conservation of energy….the so called ‘starvation mode’.

Does fasting cause muscle loss? 

Not a lot of credible studies have examined the effects of regular fasting, on muscle retention. But it’s safe to say that during  prolonged fasting protein catabolism (breakdown) becomes an issue. In order to maintain blood glucose, amino acids are converted into glucose (glucogenesis); if amino acids are not available from food, protein must be taken from bodily stores such as muscle leading to tissue loss. Research found that amino acids from muscle contributed 50% to glucose maintenance after 16 hours and almost 100% after 28 hours, after full depletion of liver glycogen.

What it means to you ma darlin’:

Fasting falls in the two categories of short-term and prolonged . The former is safe, the latter…not so much. Despite what you’ve heard, slipping into the starvation mode is not very likely with skipping a meal or breakfast (see here).

For those looking to increase muscle mass, before fasting consume a slow digesting protein such as casein (eg. cottage cheese) along with a bit of fat, to ensure availability of amino acids.


[1] Energy metabolism after 3 days of fasting
[2] Resting energy expenditure in short-term starvation is increased 
[3] Enhanced thermogenic response to epinephrine after 48-h starvation

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