Below follows a brief, and a bit informal, e-mail exchange with Matt Metzgar on intermittent fasting and how it can be used for muscle growth and fat loss.

It may answer some questions the new reader may have about my methods, so I thought I'd put it up here.

New readers may also wan't to read the interview I did with Leigh Peele, where I delve a bit deeper into the Leangains methodology and explain how it evolved from the beginning. You'll find it here.



Martin, I came across your website and think it is terrific. I mentioned it on my blog the other day as well (www.mattmetzgar.com). I had a question for you, since you seem to have done a lot of experimentation with intermittent fasting (IF). First off, I am a big fan of IF and use it occassionally. I think it's a great tool for getting leaner without losing muscle mass. My question is, can intermittent fasting impede muscle growth?


If you're referring to gene expression that might get activated by the fasted phase, there is one study showing gene expression for proteolysis after 40 hours of fasting. To my knowledge, none of the popular IF regimes out there (Leangains, Fast-5, Eat Stop Eat, Warrior Diet) uses more than 24 hours max. In that context, my answer to your question would be no.

My hunch is that it might actually be other way around - since IF improves insulin sensitivity, it might equal more favourable nutrient partitioning when you feed. Simply put, more calories might get used for muscle growth and recovery processes (amino acids to muscle, carbs to glycogen stores) in trained individuals vs the amount that would get stored in fat cells, had you been eating with regular intervalls. That is, of course, speculation from my part as there is no hard data on trained individuals to suggest such a thing.

There are of course other ways, aside from the hormonal/physiological side of things, that IF may impede muscle growth, or cause muscle catabolism; an insufficient protein intake and poorly matching calorie intake to energy expendiure (resulting in a large calorie deficit) for example, but this goes for every dietary approach out there.



I wonder if IF can lead to less resources being available when the body is trying to build muscle?


Well, it's a question of properly matching intake to expenditure. A large protein intake in your last meal will result in the body having amino acids available during the sleep and the fasted phase. For reference sake, 30-40 g casein or animal protein takes 7-8 hrs to fully digest, during which time amino acids are trickled into the blood stream for growth and muscle cell repair. For my last meal, I eat much more than that. I probably still have amino acids from the foods I ate in my last meal the night before, floating around in my blood when I break the fast 16 hours later.



Also, could IF indirectly limit muscle growth by decreasing overall calorie intake? By this I mean, even if a person isn't restricting calories, they may find it hard to eat enough in the compressed window to get enough food in.


This would only be a problem for a very small majority of people, and I'm sure even they could amend the problem by eating more calorie dense foods.



One last related question: putting aside the issue of IF, what have you noticed as far as building muscle in a calorie deficit, sufficient calories, or a calorie surplus?


IF aside, building muscle during a constant calorie deficit is generally only possible for beginners or people taking up weight training again after a layoff (muscle memory). Using a cyclic diet approach, such as the way I generally structure IF diets, is another thing and may allow muscle growth (though you're technically not in a calorie deficit all days of the week, the weekly calorie balance average is negative and enables fat loss as well).

By sufficient calories I assume maintenance intake/matching calories to demand in order to maintain status quo on a constant, day to day, basis. This is a tough question to answer, but since muscle growth requires a certain amount of calories above baseline, it will be obviously be limited. Again the issue of training status; I don't doubt that beginners maintaining calorie balance will grow muscle regardless, but for an experienced trainee, not much will happen, or at least not much will happen unless measured in the very long term (and even that is speculative). With a cyclic diet approach, equaling out to a weekly average of maintenance level calorie intake, I believe things are different and this mirrors my practical experience as well.

A constant caloric suplus is a sure fire way to grow muscle, but also to gain fat (the last part is one more reason I usually cycle calorie intake whether I'm dieting, maintaining or bulking).



This cycling of caloric intake is exactly what I've been thinking about! I'm thinking/hoping there has to be a way to gain muscle without fat. You see children grow and get bigger without getting fat (when eating healthy foods); you see an animal getting bigger and stronger without getting fat. My best guess now is that there could be "mini-cycles" of calorie surplus and deficit, and that can lead to a net gain of muscle without fat. For example, after a workout, you might have two days of "feasting" and most of the food is getting partioned to muscle, along with some to fat. Then you might have a day or two of deficit to lower the fat stores, while retaining muscle (perhaps through fasting and the associated GH). So there is a net surplus over this cycle, but it all ended up in muscle.

What do you think?


While your analogy to the growth processes in children and animals might be a bit faulty, gaining lean body mass in the form of muscle and not fat, is the premise behind the Leangains concept.

The way to achieve this is done by placing calories strategically, in a time period (post workout) where they are more likely to get used for muscle synthesis rather than fat gain. Seeing that protein synthesis is elevated 24 hrs post workout, it makes sense to consume a large amount of calories shortly after working out; a substantial load is consumed, then assimilated during the sleep and several hours into the fast phase upon waking, during which muscle repair/synthesis occurs. As protein synthesis declines, calorie intake is lower, allowing for fat loss.

The net result, measured over several such minicycles of workout days (higher calorie) and non-workout (lower calorie) days, will be an increase in lean body mass and a decrease in fat mass.

I guess the main question is which approach will produce the fastest results; for example, is the fast/feed system superior to a more traditional bulk and cut cycle? I have my own opinion of course, but I make no unsubstantiated claims to know the true answer. For someone like myself, putting aestethics and quality gains before a sledgehammer approach to weight gaining, it surely has it's advantages though.


End. Thanks to Matt for giving me an ok on posting the discussion here.