It is my understanding that the brain uses about 20% of our energy and ketones can provide up to 60% of that. So the brain needs about 8% of our energy in the form of glucose. So about 92% (red blood cells?) of our energy needs can be in the form of fatty acids and ketones. If a person has body fat to spare, then even if less efficient than creating glucose from amino acids, it seem like it would still be more efficient than breaking down muscle and then having to rebuild it later... Though the autophagy in the muscle cells might be worth it.
Look at data for those who have done long term fasts. Valter Longo suggests his data shows muscles and organs shrink during long duration fasts, which is why he says that refeeding is as important as fasting. Look at nitrogen balance studies on long term fasters. No matter how well keto adapted, long term fasters show a negative nitrogen balance.
Here is an article by Stephen Phinney MD PhD & Jeff Volek PhD on the topic. Phinney has been studying this since the late 70's. Scroll down to the heading: The Scientific Details. A quote from the blog, "As shown above, net protein breakdown begins within the first day of fasting, reaches its maximum rate within 2-3 days – typically a pound of lean tissue lost per day – and then slowly tapers to 'just’ a quarter pound per day after 4-5 weeks. It is also well established that extra adipose tissue does little to protect the body from this pattern and rate of lean tissue catabolism."
Tincup wrote: ↑Thu Jul 21, 2022 3:11 pm
Here is an article by Stephen Phinney MD PhD & Jeff Volek PhD on the topic. Phinney has been studying this since the late 70's. Scroll down to the heading: The Scientific Details. A quote from the blog, "As shown above, net protein breakdown begins within the first day of fasting, reaches its maximum rate within 2-3 days – typically a pound of lean tissue lost per day – and then slowly tapers to 'just’ a quarter pound per day after 4-5 weeks. It is also well established that extra adipose tissue does little to protect the body from this pattern and rate of lean tissue catabolism."
Wouldn't the loss of lean body mass be the autophagy that everyone seems to be chasing?
Does this study have no fat in the diet? How about the others?
1. Rabast et al, 1981.
Total fasting was compared with a 300 kcal/day very low calorie diet providing 56 g protein and 12 g carbs in 14 healthy obese patients, selected as matched pairs, over a period of 28 days. The weight loss was significantly greater during fasting than during the VLCD (16.5 kg vs. 12.7 kg). The basal metabolic rate showed a significant decrease (25 per cent) during total fasting, but was unchanged with the VLCD. With both diets there was no significant change in T4 or TSH, but T3 decreased along with a transient increase in rT3. Nitrogen balance was attained in five of seven patients on the VLCD after four weeks but none of the patients on the total fast.
