VLCD & Muscle Loss

Common saying: Low calorie diets cause a lot of muscle loss.

1 - If that's true, what's the science behind that?

On a low calorie diet you lose fat very fast, along with muscle.
On a regular diet you lose fat in a longer time, again along with muscle.

Why would muscle loss be greater in the first case?

2 - Also, is the variation in muscle loss between the two diets in the end large?

3 - How big would muscle loss be for large body fat percentages (25-30%) for both diets? (If body fat percentage is influential, at all)

Thanks!

Common saying: Low calorie diets cause a lot of muscle loss.

1 - If that's true, what's the science behind that?

On a low calorie diet you lose fat very fast, along with muscle.
On a regular diet you lose fat in a longer time, again along with muscle.

Why would muscle loss be greater in the first case?

2 - Also, is the variation in muscle loss between the two diets in the end large?

3 - How big would muscle loss be for large body fat percentages (25-30%) for both diets? (If body fat percentage is influential, at all)

Thanks!

Your reasoning is wrong. You lose mostly fat and little muscle when you are eating an adequate number of calories of good food. I'm a low carber and I've actually gained 4+ pounds of muscle while losing 23 pounds. My body fat has gone down considerably. If you lose 25-30% of your muscle mass you are going to be in dire trouble. Your heart is the largest muscle in your body. Remember Phen-Phen - VLCD, lots of muscle loss and lots of dead dieters. If you are working out with both cardio and strength training, your'll keep all your muscle or even gain muscle. Most of your loss will be fat and water weight. Ideally your body should be no more than 25% fat and 75% lean body mass. An remember that lean body mass also includes the weight of your bones.

That's a lot of muscle gain on a deficit. I've also learned that cardio DRIVES muscle loss; It doesn't prevent it or help reduce it.

Cardio doesn't drive muscle loss... Cardio only gets brought into the picture because so many people choose to ONLY do cardio. You have to do some strength training in order to keep your muscles. Cardio is still good exercise. You just have to balance the weight loss with muscle retention.

Common saying: Low calorie diets cause a lot of muscle loss.

1 - If that's true, what's the science behind that?

evolutionary explanation - it's what gives the human body the best chance of surviving a food shortage. Muscle cells require a lot more energy to stay alive than fat cells do. In a food shortage, the body can burn one or the other for energy (to make up the energy you're not taking in through eating because you're not eating enough to sustain your body and activity levels) - by burning muscle cells a) the body gets energy and b) the body also saves energy, as that's fewer muscle cells to keep alive. During a food shortage, the body tries to keep the fat stores as long as possible, because once they run out, you're dead. So skeletal muscle is burned in preference to fat in a severe food shortage. Unused skeletal muscle is burned before skeletal muscle that's regularly used, which is why exercise protects against muscle loss to some extent, but not indefinitely. The more severe the food shortage the more likely muscle is to be catabolised (burned) - which is why a small, sensible deficit is recommended. The leaner you are, the more likely muscle is to be catabolised in a deficit, as the body has less fat, and when fat runs out you die, and this is also why as you approach healthy levels of body fat, it's a good idea to make your deficit smaller and lose weight more slowly.

On a low calorie diet you lose fat very fast, along with muscle.
On a regular diet you lose fat in a longer time, again along with muscle.

Why would muscle loss be greater in the first case?

Because fat is what your body needs to survive a famine. By burning muscle along with the fat, you are more likely to survive the famine. This is how we evolved, because the Homo erectuses whose bodies work how you want your body to work (i.e. to burn all the fat on a VLCD and keep all the muscle) starved to death very quickly in food shortages and didn't leave any offspring in the population. We're descended from famine survivors, our bodies are very good at surviving food shortages, they do that by cataboising skeletal muscle and also through hormonal changes that result in the metabolism slowing, and also by using less energy for non-essential functions, meaining that yes you survive the famine, but you're miserable and not terribly healthy during it or for a while after it. And also, regaining a ton of body fat after the food shortage is over, is a survival mechanism, because it'll give you a better chance of surviving the next food shortage. And the next one. And the next one. It does that by storing more fat when you do get to eat properly.

If your deficit is sensible and you exercise you can drastically reduce the amount of muscle that you lose along with the fat, because you avoid setting off survival mechanisms that kick in to help you get through a food shortage. As far as your body's concerned in this context, it's still the lower palaeolithic era, so eating a VLCD = drastic food shortage = survival mechanisms kick in. BTW the first ones to kick in affect your behaviour, e.g. binge eating, food cravings, obsessing about food. Homo erectus had limited abilities to plan ahead, but obsessing about food = increase in food seeking behaviour (hunting, scavenging, gathering) = more likely to find food = more likely to survive. And of course, when food is plentiful, then binge eating = storing lots of fat = more likely to survive the next food shortage.

2 - Also, is the variation in muscle loss between the two diets in the end large?

Yes. Especially if you also do any form of exercise that works the muscles hard.

As far as your body's concerned, exercise = food aquisition. It's not going to burn muscle you use for exercise unless it really has to (i.e. in a really severe food shortage) because your body gets that it needs that muscle to aquire more food. Aquiring food in a food shortage = better chance of survival = more offspring in the next generation. We're descended from survivors of food shortages who managed to aquire enough food to get by. So exercise + mild food shortage = keeping skeletal muscle and burning fat slowly. this is what you want to emulate. A mild food shortage, i.e. a small, sensible, conservative deficit. In a severe food shortage your body will jettison muscle used in exercise, although unused muscle goes first in either case.

3 - How big would muscle loss be for large body fat percentages (25-30%) for both diets? (If body fat percentage is influential, at all)

If you have a lot more excess fat, you won't lose so much muscle while on a VLCD because you have so much fat already, the more fat you have the longer you can survive in a famine, so burning some of it off isn't going to be a big risk from a survival point of view (speaking in evolutionary terms). However someone who's already lean, isn't going to do that well in a food shortage, so survival mechanisms like burning muscle for energy will kick in sooner. VLCDs may be an option for someone that is so severely obese that the health risks from staying so obese are greater than those caused by the VLCD, and the VLCD would be used short term, and replaced by a more conservative deficit for slower, sustainable weight loss, after the person has lost enough weight to be out of immediate danger from the obesity.

25-30% is not a large body fat percentage though, the healthy range for women is 18-28%, so there is no way that anyone whose body fat percentage is 25-30% should be on a VLCD. What I'm talking about above is like 50-60% body fat or more. Someone with 25-30% body fat should eat at a very conservative deficit, probably 10% below TDEE, or aiming for 0.5-1lb weight loss a week.

Your post is kind of worrying because a) you seem to be looking for justification to go on a VLCD, and b) you think 25-30% body fat is a "large body fat percentage" when it's actually pretty much in the healthy range, and given the innaccuracy of some methods of measuring body fat percentage, 30% could be really 28% and totally in the healthy range. I hope my worries are unfounded and I'm just being paranoid because there are so many on this site who are looking for justification for their disordered eating. But in any case a) VLCDs are unsusinable and bad for health, and b) 25-30% body fat is not high at all, it's mostly within the healthy range.