Thursday, June 09, 2011

Metabolic Flexibility

Experimenting with consecutive intermittent fasting and fasted training this week(see post -The Next Level) I discovered a concept that seems to be the logical goal of my current WOE which includes both intermittent fasts and fasted training.

From the beginning of this paleo/primal journey back in 2010 I felt that what made us Homo Sapiens unique was our ability to adapt, specifically in regards to nutrition. We are the ultimate omnivores - how else do we explain how our species can thrive across the globe living in various enviroments which offer completely different food sources. We are designed to be flexible with metabolic systems cabable of adaptation to what energy sources are available.

"How I approach my personal diet is to fill the bulk of my daily food with paleo staples;grass fed meats(beef, lamb and turkey), cold water fish, greens, veggies, coconut(oil, meat and milk), some fruit(apples mostly), coffee, water and free range eggs. Firmly believing that Homo Sapiens are the ultimate omnivores (and opportunists) I will occasionally indulge in some of the foods listed above(dairy, wine, chocolate) as cheats."
                                                Rolfdevinci « Reply #24 on: December 18, 2010, 02:08:27 PM »

It was through investigating fasted training that I stumbled upon the idea of metabolic flexibility. In essence it suggests that the aim of any dietary regimen has the goal of enabling our bodies to gather nutrients, norishment and, most importantly,energy from a variety of sources.

"Human physiology needs to be well adapted to cope with major discontinuities in both the supply of and demand for energy. This adaptability requires 'a clear capacity to utilize lipid and carbohydrate fuels and to transition between them' (Kelley et al. 2002b). Such capacities characterize the healthy state and can be termed 'metabolic flexibility'..."

In laymans terms(or at least my understanding of) is that metabolic flexibilty is the ability of the body to easily switch back and forth from burning carbs, proteins and fats for fuel(energy) based on the availability of food sources.Perhaps that is the ultimate evolutionary gift - the ability to switch our metabolic furnaces to burn whatever sources of energy are available at any given time.

“A greater reliance on fatty acids for fuel, along with the ability to conserve and replenish muscle glycogen, offered a distinct survival advantage as it allowed our Paleolithic ancestors to work (i.e., hunt and gather) longer and more often” –Loretta DiPietro, PhD, MPH

The opposite of metabolic flexibility is metabolic inflexibility or a state where we have forced our bodies to depend upon one source of energy over the others to the detriment of the whole metabolic process. That would explain, for example, why high carb eaters suffer the notorious carbohydrate "bonk"  being unable to effectively switch over to burning fat reserves when muscle glycogen is expended. In a worse case scenario chronically impaired metabolic processes =  the development of "diseases of civilization" = metabolic syndrome.

By adopting a low carb WOE I began the process of forcing my metabolism to shed it's reliance upon carbohydrates as a primary fuel and forcing it to accept both protein and fat as viable sources of energy. I am able to exercise efficiently in a fasted state(and not bonk) and able to exercise efficiently in a fed state.My metabolism is able to choose what fuel it wants to burn.

" Metabolic flexibility is teaching the body to use the right fuel at the right time. Long term, we want to teach the body to be as adaptable as possible.Better Adaptability = Health"

  In terms of endurance athletics one can improve their metabolic flexibility and performance by(periodically) training in a fasted/glycogen depleted state......

"In support of the benefi cial effects of training in a glycogen-depleted state, Hansen et al. (Hansen et al., 2005) have
shown that 10 weeks of training in a glycogen-depleted state resulted in an 85% greater increase in time to exhaustion
compared with training with high glycogen. The reason for this greater increase in endurance was a larger increase in
citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HAD) and other important enzymes of fat metabolism. These
results have now been confi rmed in highly trained cyclists suggesting that, regardless of the athlete’s training state,
training in a glycogen-depleted state results in an increased capacity to use fat as a fuel during exercise.........
Training in a muscle glycogen-depleted state increases an athlete’s ability to oxidize fat. In long duration endurance
competition this increase in fat oxidation may spare muscle glycogen and improve performance.

Very interesting stuff.

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