Saturday, April 19, 2008

Training in a fasted state

I know a few of you out there practice Intermittent Fasting (e.g. Eat Stop Eat or Leangains) and also train in various ways.

If you do IF you may be a little worried about training on days you haven't eaten. I've done it and haven't found it a problem even after a 24 hour fast. There is all sorts of science about training in a fasted state (or a carbohydrate restricted state which is similar.......)

In any case this study might be of interest - short-term training elicits similar adaptations in peak O2 whether carried out in the fasted or carbohydrate-fed state. Obviously normal caveats - e.g. the abstract doesn't explain what "fasted" means.

Matt had some posts a while ago reflecting on the fact that for a hunter exercise would generally be in the fasted state - i.e., when you ran out of food and got hungry you had to exercise (hunt) to get some food. Hence exercise would often be in the fasted state - so it is something we should be adapted to.

Effect of training in the fasted state on metabolic responses during exercise with carbohydrate intake

Skeletal muscle gene response to exercise depends on nutritional status during and after exercise, but it is unknown whether muscle adaptations to endurance training are affected by nutritional status during training sessions.

Therefore, this study investigated the effect of an endurance training program (6 wk, 3 day/wk, 1–2 h, 75% of peak O2) in moderately active males. They trained in the fasted (F; n = 10) or carbohydrate-fed state (CHO; n = 10) while receiving a standardized diet [65 percent of total energy intake (En) from carbohydrates, 20%En fat, 15%En protein].

Before and after the training period, substrate use during a 2-h exercise bout was determined. During these experimental sessions, all subjects were in a fed condition and received extra carbohydrates (1 g·kg body wt–1 ·h–1). Peak O2 (+7%), succinate dehydrogenase activity, GLUT4, and hexokinase II content were similarly increased between F and CHO. Fatty acid binding protein (FABPm) content increased significantly in F (P = 0.007). Intramyocellular triglyceride content (IMCL) remained unchanged in both groups.

After training, pre-exercise glycogen content was higher in CHO (545 ± 19 mmol/kg dry wt; P = 0.02), but not in F (434 ± 32 mmol/kg dry wt; P = 0.23). For a given initial glycogen content, F blunted exercise-induced glycogen breakdown when compared with CHO (P = 0.04). Neither IMCL breakdown (P = 0.23) nor fat oxidation rates during exercise were altered by training.

Thus short-term training elicits similar adaptations in peak O2 whether carried out in the fasted or carbohydrate-fed state. Although there was a decrease in exercise-induced glycogen breakdown and an increase in proteins involved in fat handling after fasting training, fat oxidation during exercise with carbohydrate intake was not changed.


Eugene Thong said...


Interesting study. I wonder what the outcome would have been if:

1) The subjects were being tested in a glycolytic/high intensity activity instead of an endurance bout.

2) The F subjects had been following a controlled-carb diet instead of the 65-20-15 diet in the study (so that they would have been "fat-adapted").

3) If the researchers had tested power output or some other performance marker instead of peak O2.

It's unusual to me that the F group had no advantage in fatty-acid oxidation but this is probably due to the researchers loading them up with carbs during the exercise bouts.

You continue to astound me with your incredible finds. Thanks!

Keenan said...

I would add that not only would an evolutionary outlook explain man's success at hunting while fasting, but that being in top form while fasting was probably crucial.

Can you imagine a *missed* hunt? All that exertion, all that effort, and nothing to show for it? It would make sense for performance to be at *peak* while fasting, since that's when hunting would occur.

I know I feel mentally sharper and physically stronger and lighter on an empty stomach, and I have heard the same from many fellow IFers.

Great post, keep this excellent research coming!

Chris said...

Thanks Keenan - that makes sense

Steven said...

one's body has to put energy into digestion so performance would be higher on an empty stomach I would think. think of the urge to take a nap after a large meal.

Chris said...

Steven - thanks for the comment. I don't totally agree - not all meals make you sleepy. I can't recall the last time bacon and eggs made me sleepy. But I know that anytime I have a big plate of pasta, I'm out like a light about 30 minutes after I'm done eating. Carbs are an issue too.