The FastDay Forum

http://www.ncbi.nlm.nih.gov/pubmed/11574981

I haven't seen the full paper, but thought this was interesting.

Having tested meals of variable composition ahead of a 24 hour water and food fast (nil by mouth ?) found that the ~50% protein meal was the most challenging fast in terms of subjective assessment in a cross-over trial.

The main laboratory findings were a 40% increase in blood urea nitrogen and higher urine osmolarity after the protein-rich meal than after the other meals.

Conclusion:
"A protein-poor pre-fast meal is likely to be followed by easier fasting"

A 50% protein dinner of 600 calories would be 75g of protein, for illustration (don't know what they did in the paper).

[carorees]

Interesting that they do not report notable differences between the carb rich or fat rich meals in the abstract. If you look at the "related citations" you can see some papers discussing differences in thermogenesis and substrate metabolism with different meal compositions. One could speculate that the fast following a protein rich meal would start with the organism already low in energy stores compared with a high fat or carb meal?

The related titles are interesting, yes. The one with 100% higher thermogenesis is less high in protein than the OP....

"In a randomized trial, 65 healthy, overweight and obese subjects consumed ad libitum a high-protein (HP), reduced fat diet (24% energy from protein, 29% energy from fat) or a high-carbohydrate (HC), reduced fat diet (59% energy from carbohydrate, 29% energy from fat) for six months "

one of the others contradicts..

"Diet-induced thermogenesis and substrate oxidation are not different between lean and obese women after two different isocaloric meals, one rich in protein and one rich in fat."

back to hunting for protein loss in fasting..............

If protein is available (or the only thing available) would the body not choose to use it for energy rather than muscle repair etc? I always thought that burning protein as a fuel was bad (and wasteful). But if protein is to be spared for repairs, why do we count its calories? How does one's metabolism decide which & what percentage of the available fuels (glycogen, fat, protein)should be burned at any particular time. Just wondering what 1/2 tin of tuna for breakfast on a fast day actually does for you...

The body usually has a reserve of glycogen of 1-2000 cals and fat of tens to hundreds of thousands of calories so the need to use protein as fuel shouldn't arise.

I think we count the calories because the energy balance applies and unless the protein exits the body as protein there is an energy difference to account for.

So what does this mean in a nutshell? I should eat pasta and pizzas the night before my fast? I did that last week, and it worked pretty well. No pain on fast day. None at all.

The body usually has a reserve of glycogen of 1-2000 cals and fat of tens to hundreds of thousands of calories so the need to use protein as fuel shouldn't arise.

I think we count the calories because the energy balance applies and unless the protein exits the body as protein there is an energy difference to account for.

In that case following Dr. M's advice and eating high-protein meals on fast days should have the knock-on effect of burning more fat as well as mitigating against muscle deterioration, no?

[carorees]

Any excess protein eaten (over that required for repair) is converted to glucose and used for energy.

I guess this was my question - are repairs prioritized when protein is the only food available and glycogen is being burned already, or is protein gleefully burned as a source of energy? If excess protein is carcinogenic, is it not because it is being used as a fuel rather than a repair material?

[carorees]

Yes, repair comes first. Growth hormone released during fasting and the drop in insulin pushes the body towards using fast rather than protein. But left over protein is used for fuel. You may be right about the excess protein and cancer because certain metabolic pathways used by cancer cells to enable growth appear to be upregulated when there is a lot of protein and glucose in the diet.

Protein isn't stored so if not used for repair then it's used as fuel. Typically we are assumed to be 15% fuelled by protein.

The take home message for me is not to go mad with protein at the "last supper" in a vain attempt to cover for the fast. A balanced meal would be fine and in general anything over 35% protein is seen as excessive.

Personally I don't see evidence for high protein on fast days. Several trials are at 30g or less. One apocryphal holiday tweet doesn't erase the ADF or true fast evidence, even if it wasn't an error.

[Tracieknits]

So what does this mean in a nutshell? I should eat pasta and pizzas the night before my fast? I did that last week, and it worked pretty well. No pain on fast day. None at all.

This is a great question. I think I'm going to give it a shot this week and see how it goes

A dumb question: What relevance is this to 5:2/4:3 since in these "fast" is a misnomer (500/F 600/M cals a day)?

In contrast this study seems driven by "real" fasts - "Fasting is required by the Jewish and Islamic religions".

A dumb question: What relevance is this to 5:2/4:3 since in these "fast" is a misnomer (500/F 600/M cals a day)?

In contrast this study seems driven by "real" fasts - "Fasting is required by the Jewish and Islamic religions".

Good question -- note also the fasts studied here included water deprivation as well. I can't help but think that has a huge effect. We don't restrict water intake at all -- in fact, we encourage people to drink more water than usual to make up for the water they're not getting in the food they're not eating.

[Tracieknits]

Many of us on 5:2 actually do fast until dinner, and our fasts are in some ways more restrictive than a Ramadan fast in that we don't wake up before the sunrise and have a feast before our fast day. So many of us are going 22 hours of fasting on our fast days.