Fasting and its impact on muscle

I've been eating between 450 and 1000 calories per day, within a 6-hour or so window each day, for the past week or so. Due to the lockdown I'm working from home all the time so I'm sedentary. It's all low-carb food - mackerel, almonds, pecans, eggs, salmon, etc. - and the really surprising thing is I'm actually not hungry and that's why I'm simply not eating as much. Last night I went as far as 1100 calories but I did that just to eat to be safe, not that I was hungry. (I'm drinking c. 6 litres of water per day)

My chief concern, and why I'm eating more than I want to eat, is that the common advice is if you don't eat enough you lose muscle, rather than fat (I was over 30kg above my BMI max weight when I started this Monday week last).

Jason Fung, however, has a piece in his The Complete Guide to Fasting (p. 75), entitled "Myth #2: Fasting Makes You Burn Muscle" says the following:

'One persistent myth of fasting is that it burns muscle, that our body, if we’re not eating, will immediately start using our muscles as an energy source. This does not actually happen.... Muscle, on the other hand, is preserved until body fat becomes so low that the body has no choice but to turn to muscle. This will only happen when body fat is at less than 4 percent. (For comparison, elite male marathon runners carry approximately 8percent body fat and female marathon runners slightly more). If we did not preserve muscle and burn fat instead when no food is available, we would not have survived very long as a species. Almost all mammals have this same ability.... Rather than burning muscle during fasting, we start conserving muscle. Much of the amino acids that are broken down during regular turnover of cells are reabsorbed into new proteins.”

[https://www.researchgate.net/publication/335463392_Complete_summary_notes_on_Jason_Fung_MD_UCLA_Adult_Nephrologist's_book_The_Complete_Guide_on_Fasting_on_the_effective_management_etiology_and_reversal_of_Type_1_and_Type_2_Diabetes_and_non-surgical_we]

Given how much I am overweight, is it safe to continue on these 1000 calories per day if I'm not hungry for as long as I'm not hungry, or should I eat for the sake of making a minimum calorie target per day? (The My Fitness Programme/MFP app, for instance, doesn't accept any complete diary under 1200 calories for a guy.) Thanks.

Cill94

I'm afraid this Jason Fung's views are not reflected by science or experts on the science. He has blocked a number of people like Layne Norton who have taken him to task on his claims. He doesn't want to back up claims, just sell his books.

That doesn't mean that intermittent fasting can't help you lose fat, but the mechanism it does that is simply by reducing your calories. However any diet has to be sustainable for the long term or it's a waste of time and energy.

I would say you are eating far too few calories and this is likely unhealthy at worst, unsustainable at best. Have you considered seeing a dietician?

Mellor

Muscle, on the other hand, is preserved until body fat becomes so low that the body has no choice but to turn to muscle. This will only happen when body fat is at less than 4 percent.

This is completely false. I’d go as far to say he is not simply mistaken, but willfully lying.

If it were true, we’d retain every ounce of muscle we put on. And we’d all jacked at 10% bf. In fact his own example of marathon runners at 8% contradicts his point. Elite runners clearly burn off muscle due to their energy needs. Was was supposed not possible at 8%.

The reality is there is a upper limit to the fat you can burn in a day. It’s proportional to the fat you can use for energy. Beyond that any additional deficit pretty much has to be muscle.
Plus a portion that are burned as ketones, maybe.

partyguinness

Mellor wrote: »

This is completely false. I’d go as far to say he is not simply mistaken, but willfully lying.

If it were true, we’d retain every ounce of muscle we put on. And we’d all jacked at 10% bf. In fact his own example of marathon runners at 8% contradicts his point. Elite runners clearly burn off muscle due to their energy needs. Was was supposed not possible at 8%.

The reality is there is a upper limit to the fat you can burn in a day. It’s proportional to the fat you can use for energy. Beyond that any additional deficit pretty much has to be muscle.
Plus a portion that are burned as ketones, maybe.

I might weigh in here. I am a marathon runner and about 9/10% body fat at the moment which is actually too high (6-7% is more ideal). But I can go on a drive over the next 2-3 months and get to this point

When I went on a drive to lose excess body fat last year I also lost a good bit of muscle mass which did not impact on my performance (in fact I improved in line with expectations). This is normal in the context of sports training and nutrition. Having said that you do not wish to lose too much muscle and keep your protein levels in order. More muscle = more energy requirements.

As you said if Fung was correct then I would have stripped down body fat but retained muscle which did not happen. There is a reason marathon runners are so skinny- they do not need extra muscle.

Lady Lixnaw

Hi Anamcheasta, Well done on starting on a good eating lifestyle. I highly recommend Dr. Michael Mosley and Dr. Clare Bailey's Quick and simple recipes The Fast 800 Easy Recipe Book 2020 and intermittent fasting. Also have you come across Dr. Francoise Wilhelmi de Toledo's Buchinger Clinic on Fasting on Youtube?. Sugar is the enemy and any food that converts into glucose in the body is the enemy. This includes fruits(fructose) and all grains including porridge. The body will use sugar first for fuel. When sugar is cut out, the body then turns to burning fat for energy. This is what is needed - fat for fuel. Glucose intake inhibits the burning of fat and causes spikes in hunger pangs. Cut out sugar intake and hunger pangs go, as you've experienced. Milk is lactose - sugar, cut it out. Use cream instead if needed. Furthermore all grains are intensively sprayed with chemicals before and upon harvesting of the grain. Fats and proteins are good. This is a re-education programme as well as a healthy eating lifestyle. Low carb, good protein and fat are the healthy options. Dr. Jason Fung most recent video is on Use Muscle to Keep Muscle. Dr. Berry and Dr. Berg and numerous others are on Youtube. Keep going this is a new way of life with added health benefits.

Dial Hard

450 "clean" calories + 6 litres of water a day sounds like a recipe for hyponatremia to me. Why do you feel the need to drink so much water???

partyguinness

Dial Hard wrote: »

450 "clean" calories + 6 litres of water a day sounds like a recipe for hyponatremia to me. Why do you feel the need to drink so much water???

You are heading for a world of headaches and electrolyte loss right there.

lee_baby_simms

I saw an interview with Dr Valter Longo where he hypothesised that fasting does reduce muscle mass but that mass comes back during refeeding, I've no first hand experience of this myself but Longo is a fairly well respected expert in the field.

I wouldn't consider Jason Fung to be a leading light these things, he states a lot of truths but oversimplifies others to the point of just being plain wrong.