Wanting to understand physiology with respect to energy consumption and storage

This topic contains 11 replies, has 5 voices, and was last updated by Apricot 8 years, 7 months ago.

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bigbooty

9:58 pm
23 Dec 15
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I have a good grasp of science but biology is not my field, so wanting to get the basics right. Please correct my concepts that are incorrect. We have glucose floating around in the blood between certain upper and lower bounds. Excess is stored as glycogen in muscle cells and the liver. Once these are full further excess is stored as fat either as inter-muscular fat or in adipose cells. Have I got that right?

With regards to fasting and energy consumption, depending on the rate of exercise a different mix of the three energy sources is utilised but all three are used simultaneously? Correct? As the fast continues, say a consecutive 2 day fast, the glycogen reserves will be empty and energy will be purely coming from fat stores. Correct? My question is, are the glycogen stores only replenished by once again eating after the end of the fast? Or is some of the stored fats converted and stored as glycogen during the fast? Is the body converting energy stored as fat into energy stored as glycogen because that is a better way of storing energy that is more readily usable for daily activity and exercise?

TishC

6:53 pm
16 Apr 16
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Hi there,

A fab question and one I’m keen to know the answer to as well – I noticed there are a lot of unanswered questions so maybe the forum isn’t that well used ? But that has posed some research for me 🙂 If I find out anything I’ll post a reply 🙂 if you’ve found the answer could you share a link ?

simcoeluv

7:07 pm
16 Apr 16
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Hi:

A quick answer to big’s second paragraph. After the glycogen is depleted, the body then converts muscle for energy. It continues to do this for up to 14 days as the body ramps up its fat burning. As the body starts burning more fat, it burns less muscle. The body does not convert fat to glycogen. Stored sugars basically come from dietary sources.

Apricot

5:21 pm
21 Apr 16
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Hi Simcoeluv. Did you mean using the fat in your muscle maybe? An interesting extract on the myth of muscle loss from Dr Jason Fung:

“Myths of intermittent fasting

“•Fasting will make you lose muscle/burn protein. ……
[other myths listed in here]………
If these myths were true, none of us would be alive today. Think about the consequences of burning muscle for energy. During long winters, there were many days where no food was available. After the first episode, you would be severely weakened. After several repeated episodes, you would be so weak that you would be unable to hunt or gather food. Humans would never have survived as a species. The better question would be why the human body would store energy as fat if it planned to burn protein instead. The answer, of course, is that is does not burn muscle in the absence of food. That is only a myth.”

“Studies of alternate daily fasting, for example, show that the concern over muscle loss is largely misplaced. Alternate daily fasting over seventy days decreased body weight by 6 per cent, but fat mass decreased by 11 . 4 per cent. Lean mass (including muscle and bone) did not change at all. Significant improvements were seen in LDL cholesterol and triglyceride levels. Growth hormone increased to maintain muscle mass.”

simcoeluv

6:37 pm
21 Apr 16
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Hi Apricot:

I meant what I said. Some argue that intermittent fasting burns less muscle because the body does not burn through all of the available glycogen before eating resumes. But the research shows all known diets burn some muscle – some more than others. My example above is the pattern for those that are doing long term water fasting.

Apricot

12:24 am
22 Apr 16
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According to Jason Fung , that is a myth. Ditto Dr Ludwig at Harvard.

simcoeluv

1:18 am
22 Apr 16
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Hi Apricot:

There is decades of research that shows that muscle is burned during diets. The body cannot live on fat alone – it needs protein provided by muscles to survive.

If you notice the last sentence of your quotation – “Growth hormone increased to maintain muscle mass.” – you can understand that muscle is being ‘burned’ but some of it is being replaced when food is eaten. It appears that IF burns less muscle mass than standard diets do – 10% v. 25%, but to claim no muscle is burned when doing IF for weight loss is incorrect according to the current research. Here is a brief discussion and compilation of some of the research: http://www.leangains.com/2011/03/intermittent-fasting-for-weight-loss.html. Varady’s study is also interesting and shows a 1 kg. muscle loss in 12 weeks on ADF: http://onlinelibrary.wiley.com/doi/10.1002/oby.20353/full

simcoeluv

1:30 am
22 Apr 16
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Hi Apricot:

I forgot to mention that the only study I am aware of on 5:2 (Harvie) showed a 1.2 Kg. loss of muscle weight over the 6 months of the study (about 10.5% of total weight lost): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3017674/

bigbooty

3:19 am
22 Apr 16
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Ive read and agree that there is some (small amount of) muscle loss associated with dieting (Dr Peter attia blog). I don’t think this is a major worry and has been blown out of proportion by vested interests. It is the power to weight ratio that is important if you are really that sports focussed. And for most people on this forum I really don’t think that’s the case (without sounding rude). If I lose 10kg of fat and 1kg of muscle mass I suspect that overall loss of weight and slight loss of muscle means that really Im miles ahead. Power vs weight has gone up.

Attia’s blog also said that even on his ketogenic diet that glycogen is replenished after it is consumed to about 60-70% of what would be a “normal” level would be after sleep. So the body is restoring the lost glycogen even in the absence of lots of carbs. Im not sure of the physiology of how this is occurring though.

I know that when I have done a very strenuous bike ride all I crave is protein. So the body is telling you what you need. I think even the most modest of exercise will offset any muscle loss due to dieting.

HappyNow

8:21 am
22 Apr 16
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Bigbooty,

I agree with you. Power to weight is key.

I’m not sure why people have got so hung up about muscle loss from dieting. It seems fairly obvious that the more you weigh the more muscle you’ll need (and that includes the heart), and as you lose weight you don’t need to maintain that same muscle mass.

Apricot

10:14 am
22 Apr 16
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It’s becoming fashionable in the body building community to use fasting to help build muscle. They mostly seem to use the 16:8 timing, that is, eating within an 8 hour window. Here’s one of many articles on the subject.
http://greatist.com/fitness/why-you-should-exercise-on-an-empty-stomach
By the way the item I put in at length above was not in my words but Jason Fung in his book just published. I copied the block and only left out the list he had of other myths.

There is a change in the way exercise seems to be being viewed in parts of the health community : no longer to increase the use of calories in the cals in cals out system, as it’s been well documented that the body compensates by making you slightly hungrier, but rather because it has a hormonal effect within the liver and in the use of the fat cells that are sited within the muscle. As people get older and more sedentary they lose muscle density. But building this back again is both possible and desirable. There’s a YouTube lecture clip on this which I will post when I’ve time to seek it outagain.

Apricot

10:45 am
22 Apr 16
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HappyNow, I think it may have come across from studies of anorexia nervosa, where muscles get wasted when people begin to get down to a very low body weight and the heart, being a muscle, can thin and fail, as do other organs in this very drastic condition. But even among this community heart effects are not universal.