The FastDay Forum

Feel free to merge into the other thread on protein if appropriate.

I did quite a bit of reading into fasting and muscle / protein loss, to the point of saturation. Here are some links with the messages I took away from them....

In http://jp.physoc.org/content/590/5/1049.long "Muscle protein synthesis in response to nutrition and exercise" it is stated that increased muscle protein synthesis (MPS) occurs on feeding with protein due to increased amino acid availability. "Nutrient-driven increases in MPS are of finite duration (∼1.5 h), switching off thereafter despite sustained amino acid availability and intramuscular anabolic signalling." - in other words the post-meal muscle building period is finite, although extended by resistance exercise at high load. A maximum useful dose of 20g of protein is suggested as providing sufficient amino acids to sustain MPS after eating - any more can't be used in the time available.


SKELETAL MUSCLE METABOLISM IN EXERCISE AND DIABETES Book Series: ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY Volume: 441 Pages: 307-319 Published: 1998 says that "Muscle proteins turn over slowly and there are minimal diurnal changes in the size of the muscle protein pool in response to feeding and fasting. Nitrogen balance and tracer studies indicate that protein oxidation and net protein breakdown (degradation - synthesis) is not increased during dynamic exercise at intensities of less than or equal to 70% VO2max."

http://www.ncbi.nlm.nih.gov/pubmed/9240936 is a useful overview...
"A continuous turnover of protein (synthesis and breakdown) maintains the functional integrity and quality of skeletal muscle. Hormones are important regulators of this remodeling process. Anabolic hormones stimulate human muscle growth mainly by increasing protein synthesis (growth hormone, insulin-like growth factors, and testosterone) or by decreasing protein breakdown (insulin)."

http://jn.nutrition.org/content/130/7/1868S.full "Dietary Protein and Nitrogen Utilization" includes a graph showing that the turnover of body protein per kg of body weight is much higher than the protein intake :



http://jap.physiology.org/content/106/4/1374.full has more about timing of food relative to exercise and effect on protein synthesis.

http://www.ncbi.nlm.nih.gov/pubmed/6408111 "Whole body protein breakdown rates and hormonal adaptation in fasted obese subjects." reports that the breakdown rate after 7 days of fasting is reduced from the 1.96 g/kg.day of a 12-hour fast to 1.54 g/kg.day.

PhilT wrote: A maximum useful dose of 20g of protein is suggested as providing sufficient amino acids to sustain MPS after eating - any more can't be used in the time available.

Looks like I accidentally hit on a good solution with my fast-day breakfast of a small tuna can, which contains about 16g of protein, with the juice of half a lime and a bit of salt/pepper. Weighs in at about 70 calories and leaves me free to have a quite substantial evening meal.

This study (http://www.ncbi.nlm.nih.gov/pubmed/23266375) investigated whether people who fast before exercising injure their muscles more or less than people who don't. They looked at indicators of exercise-induced muscle damage in 29 volunteers (average age 22yrs) who either fasted for 8 hours water-only or ate a controlled diet in the 8 hours before exercising in the laboratory. Muscle pain, resting elbow extension, upper arm girth, isometric strength, myoglobin, total nitric oxide, interleukin 1beta, and tumour necrosis factor alpha were measured before and after arm exercises (elbow flexors) on five separate sessions. Overall, the measurements showed no major differences between the two groups. However, some of the biochemical markers were significantly different in the fasting group than the non-fasted group.


This study of ADF and endurance exercise found that "Body weight was reduced (P < 0.05) by 6 ± 4 kg, 3 ± 1 kg, and 1 ± 0 kg in the combination, ADF, and exercise group, respectively"
Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady
Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans.
KA.http://www.ncbi.nlm.nih.gov/pubmed/23408502

Thanks Caroline. Unfortunately the first study seems to raise as many questions as it answers. Is post-exercise raised NO + lowered TNFa in fasting subjects (compared with non-fasting) good or not?

Any info on the idea that for fasters it is good to take in some food (protein? sugars?) shortly after exercise to limit muscle damage?

there seems to be at least bro-science that suggests taking in protein after exercise facilitates the repair process, though the OP suggests that below 70% of VO2max there's no increase in protein turnover to compensate for.

Thanks Phil, your post took me back to your OP to study it a bit more closely. I like the graph (3rd study), which suggests that the amount of protein intake to maintain stable level lean body mass is a little below 0.77g/kg/day - which fits well with the 0.8g/kg/day figure that has been mentioned before. But how do its figures for gross protein degradation (c.4g/kg/day) reconcile with those mentioned in the 5th study (1.5-2.0g/kg/day)?

The 5th study is in obese subjects, the 3rd in subjects variously described as "healthy" and "normal" so part of the difference may be due to expressing it per kg of body weight rather than per kg of lean mass. I don't know what the protein intake in the diet was.

The 5th quotes protein degradation after 12h and 7 days of fasting, the graph from the 3rd shows "Each bar represents the mean between postabsorptive (12 h) and postprandial (12 h) measurements " and "N balance was estimated during a 48 h period of consecutive 12 h periods of feeding hourly meals and fasting, after 12 days of adaptation to diets containing 0.36 +/- 0.01, 0.77 +/- 0.03, 1.59 +/- 0.08 and 2.31 +/- 0.65 g of protein day-1 kg-1"

There is a suggestion of a vicious circle effect in a source paper "Thus one component of the protein requirement for N balance reflects a demand for repletion of fasting losses which increases with increasing habitual protein intake." ie the more protein you routinely eat the more you'll lose while fasting.

Thanks. Yes it would be more logical wouldn't it to talk about optimal protein intake relative to lean body mass - except that most of us don't know what ours is!

If the obese subjects in study 5 had body fat c.45% and the healthy subjects in study 3 has body fat c.25% that would account for most of the apparent difference I suppose.

The 'vicious circle' makes sense to me. If the body is used to a substantial protein intake then maybe when it temporarily runs short of protein it carries on merrily breaking down old body tissue because it expects to be able to replace the lost tissue in the future when the dietary protein supply is restored. If habitual protein intake is low the body must run at a lower level of autophagy. This would suggest (to me!) that you need to maintain the optimal level of protein to keep autophagy (a good thing) going at full tilt. Without of course having too much...

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3150311/

This study compared the effects of alternate day fasting (ADF), calorie restriction (CR), and endurance exercise on LDL and HDL particle size in overweight and obese subjects

For what it is worth.

Thank you, simcoeluv, for posting the link to the study. It seems that combining 5:2 with endurance exercise might be the way to go for improving lipid levels! As that is a goal of mine, I'd better get with it!