I spent the morning catching up on some reading today, and came across a very interesting study in Acta Physiologica Scandinavia – The journal of the Scandinavian physiological society. In this study the effects of a 3-day fast on regional lipid and glucose metabolism was examined.
The authors found the typical benefits that are associated with fasting:
- No decrease in Energy Expenditure – metabolic rate DID NOT slow down
- A decrease in RQ – indicating an increase in fat burning
- Increased blood flow – some very impressive numbers, I challenge any “NO” supplement to show this kind of data!!
- Decreased blood insulin levels – Considered to be one of the major health benefits of fasting
- Increased glucagon levels – more reliance on body fat as a fuel source
- Increased Growth Hormone levels – Anybody who has read Eat Stop Eat knows that I think this is one of the major keys behind the benefits of fasting
- Increased noradrenaline – More fat burning hormones
- No increase in cortisol – No reason to think that muscle is being broken down
One of the major things that caught my eye in this paper was the great graph showing the change in fuel sources that were fueling metabolism.
You’ll notice that the amount of calories being burned are roughly the same (about 2000 Kcals), however during fasting a lot more of these calories are coming from fat. And, since the subjects were not eating any fat while fasting, this fat must have been body fat.
Another interesting finding was that the majority of this fat was either stomach fat or muscle fat.
While I would not recommend fasting for 3 days straight (I prefer 24 hours), this study does add evidence to the idea that fasting can be an effective method of reducing calorie intake, and does not negatively effect metabolic rate, or muscle mass.
(Gjedsted J, Gormsen LC, Nielsen S, et al. Effects of a 3-day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue. Acta Physiol 2007, 191, 205-216.)