I just read Eat Stop Eat and it is mentioned in the book that you MUST weight lift to not lose muscle. What if I can't lift? Will I lose muscle if I do not lift weights even if I am active in other ways? He does not elaborate on the subject so it has left me a tad bit confused.
I found this on the Lean Gains webpage! Perfect!
This myth hinges on people's belief it's important to have a steady stream of amino acids available to not lose muscle. As I explained earlier, protein is absorbed at a very slow rate. After a large high-protein meal, amino acids trickle into your blood stream for several hours.
No studies have looked at this in a context that is relevant to most of us. For example, by examining amino acid appearance in the blood and tissue utilization of amino acids after a large steak, veggies and followed up with some cottage cheese with berries for dessert. That's easily 100 grams of protein and a typical meal for those that follow the Leangains approach. We are left to draw our own conclusions based on what we know; that a modest amount of casein, consumed as a liquid on an empty stomach is still releasing amino acids after 7 hours. With this in mind it's no stretch to assume that 100 grams of protein as part of a mixed meal at the end of the day would still be releasing aminos for 16-24 hours.
Few studies has examined the effects of regular fasting on muscle retention and compared it to a control diet. None of them are relevant to how most people fast and some are marred by flaws in study design and methodology. Like this study which showed increased muscle gain and fat loss, with no weight training or change in calorie intake, just by changing meal frequency. While I would love to cite that study as proof for the benefits of intermittent fasting, body composition was measured by BIA, which is notoriously imprecise.
Only in prolonged fasting does protein catabolism become an issue. This happens when stored liver glycogen becomes depleted. In order to maintain blood glucose, conversion of amino acids into glucose must occur (DNG: de novo glucogenesis). This happens gradually and if amino acids are not available from food, protein must be taken from bodily stores such as muscle. Cahill looked at the contribution of amino acids to DNG after a 100 gram glucose load. He found that amino acids from muscle contributed 50% to glucose maintenance after 16 hours and almost 100% after 28 hours (when stored liver glycogen was fully depleted). Obviously, for someone who eats a high protein meal before fasting, this is a moot point as you will have plenty of aminos available from food during the fast.
First, why can't you lift? Is it physically impossible or are you afraid to lift? Just asking because that is important information for anyone who answers here. If you CAN lift but are afraid I can say that from experience, I was intimidated at first but after 10 years of lifting I can't imagine my life without it.
I've been a heavy lifter and a maintenance lifter and it is very important for women, especially, to create a good layer of muscle around our bones. I also IF and I never feel that I "can't" lift. Even just a 5lb weight or a light bar is enough to get some good muscle build up in your arms and legs. Though I find bodyweight exercises to be highly effective if done properly. Pilates also rocks too.
My favorite IF resource is LeanGains.com. I love that guy and he provides excellent science behind his claims. He's also very big into self-experimentation. He is quick to amend what he says if he finds new information. Read that site from beginning to end. I like it much better than Eat.Stop.Eat.
Be aware that as a woman - IF is not the same as it is for men. I'm still trying to figure itout when it comes to my monthly "gift" and after 6 months, I still have problems for a few days around that time of month.
There was a study comparing intermittent fasting with straight caloric restriction, and it was found that the intermittent fasting group maintained lean muscle mass better. This wasn't a study about weight training, so I think you should feel comfortable doing whatever exercise you can, without worrying about pushing the limit.
Sorry I can't cite the study offhand, but its abstract is on pubmed.
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