Intermittent Fasting FAQs

Intermittent fasting
Does fasting really work? Is it healthy? Can I still maintain muscle while doing it? Yes, yes and yes. And here are answers to four other burning IF questions.

I believe in thoroughly enjoying life and enjoying delicious foods, but I’m also passionate about maintaining a lean, muscular physique. Those two pursuits, by the way, are extremely difficult to balance.

That’s why I’ve been following an intermittent fasting (IF) eating plan fulltime for a while now. IF lets you eat the foods you want – within reason, of course – and still possess a shredded physique. But I’m not just now hopping on the IF bandwagon; I’ve been a proponent of it for many years.

In fact, more than a decade ago researchers from Yale along with colleagues at The University of Copenhagen explored fasting and fat loss, and the results in the lab directly helped in my own pursuits for a lean physique. Below are a handful of tips that could be useful in designing your own IF program.

But first, here’s a quick rundown of what intermittent fasting is and how it’s commonly used:

One of the main points here is this: You don’t want to undereat during your feeding window, lest you compromise your performance in the gym and your ability to build or at least mainating muscle mass. Get in all your nutrients, particularly protein. In theory, you’ll be taking in the same number of calories and macros per day, just with a different meal schedule than a typical eat-every-few-hours nutrition plan. Of course, you can always tweak calories and macros if and when your physique and training goals change.

As much research has shown, fasting for relatively long periods will result in greater fat-burning even though calories remain the same, and most people find that they’re able to have a few more of their favorite “cheat” foods during the feeding window and still see great results in getting (and staying) lean. This is why IF is such an appealing diet for many people.

Other reasons why so many individuals love IF are that’s it’s relatively easy to get used to and stick with and it’s a diet you don’t have to go off of – ever. You can do it long-term with no adverse health effects. Rather, you’ll see health benefits.

With the basics under our belts, here are four “burning” questions I often get regarding specific issues when implementing IF:

IF FAQ #1: How exactly does intermittent fasting enhance fat burning compared to a standard diet of eating every few hours?

The Yale/Copenhagen group published several papers showing that one of the key mechanisms in fasting-induced fat loss has to do with an increase in the activity of genes that increase the number of calories the body burns and the amount of fat it burns. When you fast, your body turns on genes that encode for certain uncoupling proteins and enzymes that increase fat burning. The uncoupling proteins basically “poke holes” in the mitochondria inside muscle cells. The mitochondria are where most of your energy is derived from, especially at rest. By poking holes in them, they produce less energy and thus have to burn far more calories to produce the same amount of energy in the form of ATP.

Many other studies suggest that fasting also provides numerous health benefits, such as lowering cholesterol and triglyceride levels, increasing HDL (good) cholesterol levels, and even greater longevity. One study found that intermittent fasting in men increased red blood cell and hemoglobin levels in the blood. Hemoglobin is the protein in red blood cells that carries oxygen in the bloodstream to the muscles. Increasing red blood cells and hemoglobin levels is what endurance athletes like cyclists are trying to increase when they illegally “dope” with EPO (erythropoietin). And yet IF may do this naturally!

IF FAQ #2: What should I eat as my first meal following a fast? Or does it not really matter?

Yes, it does matters. IF allows you to be somewhat loose with your eating, but that doesn’t change the fact that high protein intake is important along with healthy, wholesome food choices. Coming off of a fast, I recommend a high-protein meal as opposed to one loaded with carbs. The work from the lab at Yale found that when you fast and then re-feed with a low-carb meal, the activity of the genes that increase calorie and fat burning are further increased with the meal. However, when you re-feed with a high-carb meal, the activity of many of these genes is decreased. I recommend a high-protein meal – for example, eggs and/or a protein shake – as your initial food consumption following a fast.

IF FAQ #3: What’s acceptable to drink during a fast?

Good question. Water, of course, is perfectly fine. Other than that, opt for zero-calorie, unsweetened beverages. My personal favorites include black coffee – with no milk, cream, sugar, butter (for your Bulletproof coffee fans) or anything else in it – and plain, unsweetened tea like black tea or green tea.

When it comes to calorie-free drinks with artificial sweeteners (like flavored waters and diet soda), there’s some uncertainty. There’s some evidence to show that some artificial sweeteners cause an insulin response, which would then blunt fat-burning and contradict the fasted state, but that’s up for debate in the scientific community. To be on the safe side, I recommend not drinking artificially-sweetened beverages during a fast. If you’re absolutely dying for something other than water or plain coffee or tea during the last few hours of a fast, opt for a sparkling water that’s very lightly flavored with something like “natural lime.”

IF FAQ #4: How about BCAAs? Can I sip on those during my fast?

I get why people do this: to help preserve muscle mass while in the fasted state. But when you’re consuming BCAAs, you’re not truly fasting.

As you probably know, amino acids combine to form protein. There are 20 aminos that are used as the building blocks of protein, including the nine essential amino acids (leucine, isoleucine, valine, tryptophan, threonine, phenylalanine, methionine, lysine, and histidine), as well as the 11 non-essential amino acids (arginine, serine, cysteine, glycine, proline, alanine, tyrosine, aspartic acid, asparagine, glutamic acid, and glutamine).

If you consume just one of these amino acids, you’re essentially consuming protein and therefore are technically not fasting. The BCAA leucine poses a special problem with IF, and here’s why: The brain uses blood leucine levels as an indicator of how fed the body is, so if you’re sipping on BCAAs, the leucine is signaling the brain that you’re currently well fed. Although no work has been done on this issue during fasting, it’s easy to project that if the brain senses you’re fed, the benefits that come from fasting may be compromised. My suggestion is to avoid BCAAs and any of the 20 proteinogenic amino acids (those used in the building of proteins) until you’re in your feeding period.

Amino acids that aren’t proteinogenic can be consumed during fasting – for example, beta-alanine, betaine, D-aspartic acid and, even though they’re not amino acids (but some people classify them as such), carnitine and creatine. These are fine to sip on during the day, especially if you’re training in a fasted state.

Here's a video where I discuss this "acceptable drinks" topic with regard to intermittent fasting:

And for one more "bonus" IF FAQ – How long can I do intermittent fasting for? – watch this video:

IF FAQ #5: Is IF safe and effective for females?

Yes, intermittent fasting is absolutely effective for women. I’ve worked with many women who were seeing little results from other diets, and then they switched to IF and saw great fat loss effects. In fact, science supports this. One 2013 study showed that overweight women saw better results from IF than with a calorie restriction diet.

As for safety, an issue that’s brought up a lot is: How does IF effect a woman’s hormone levels, particularly related to her menstrual cycle?

Quick sidenote before I address this: I’ve actually done research on how exercise and nutrition effect the female menstrual cycle, so I’m not just some random trainer making this stuff up as I go. (See “Armstrong LE” reference at the bottom showing the 2005 research study I worked on.)

So, back to the safety issue of women and IF. It’s high unlikely that IF will cause hormonal imbalances in females and result in any irregularities in the menstrual cycle. Yes, it’s true that some women can experience these issues while doing IF, but when this happens it’s typically due to the individual lacking key nutrients. This would be the case with any diet – deprive your body of key nutrients and you could very well have a disturbance in your hormone levels. Your risk of this is especially high when you do a very high volume of training while keep calorie intake low. So again, this could happen with IF, but it could also happen with any other diet.

It’s also worth mentioning that, to date, no published research has shown any trend of interrupted menstrual cycles in women following IF.

The key is to make sure you’re getting your essential nutrients while following IF – essential amino acids from protein, essential fatty acids like Omega-3s, as well as key vitamins and minerals (micronutrients). If you’re training hard and dieting, you’re at risk of being deficient in the micronutrients, which is why I created Vita JYM and ZMA JYM. These two products taken should cover your micronutrient bases.

If you want feedback on IF from other women following it, I highly recommend going to the JYM Girls Facebook page. Many women in that group are doing IF and seeing great results from it.

IF FAQ #6: I’ve never tried IF, and a 16-hour fast every day sounds intimidating. Can I ease into it?

Yes, absolutely. A 16/8 IF scheme is my preferred method, but that’s not carved in stone. Here’s how to ease into IF…

First, try a shorter fasting window – something less 16 hours. Don’t forget, sleeping counts toward fasting hours, so you’re already waking up every day with at least 7-9 hours of fasting under your belt (depending on how long you sleep for). I think a good first step when trying IF is to start out with a 12-hour fast every day. In other words, a 12/12 scheme. If you had your last meal or snack at, say, 9:00 the night before, and then you wake up at 7:00am, you’ve been fasting for 10 hours at that point. Push your breakfast back two hours, to 9:00am, and that’s a 12-hour fast.

Try that 12/12 scheme for a while and get used to it, then extend your fast up to 13 hours, and see how that feels. There’s no rush here. Feel free to stay at 12/12 for a few weeks (or longer) if you want before moving up to 13 hours. However, my guess is that you’ll find a 12-hour fast is very easy and will be able to move up to 13 hours shortly after. Either way, do a 13-hour fast daily until you get used to that, then move up to 14 hours (14/10). Keep doing this until you’re at a 16-hour daily fast.

But again, a 16/8 IF plan is not mandatory. If you’re happy with the results you’re seeing with a 14- or 15-hour daily fast and want to stick to that long-term, that’s fine too. I know many people who are loving their “15/9” IF schedule.

Also, you don’t have to follow IF every single day. Follow a 12/12 scheme for only two days a week at first if you really just want to dip your toe into IF and not do it every day. If you do this, I recommend making those two day non-consecutive (ie, Monday and Thursday). From there, you can step up to a 14/10 scheme for two days a week, or do 12/12 for three or more days per week. There are any number of ways to ease into it. Find what works best for you – there are no set-in-stone rules here. It’s your diet, after all, not someone else’s.

Here’s a video of me discussing these last two IF FAQs – IF for females and easing into IF.



Armstrong LE, Maresh CM, Keith NR, Elliott TA, Vanheest JL, Scheett TP, Stoppani J, Judelson DA, De Souza MJ. Heat acclimation and physical training adaptations of young women using different contraceptive hormones. Am J Physiol Endocrinol Metab. 2005 May;288(5):E868-75.

Carlson, A. J. and Hoelzel, F. Apparent prolongation of the life span of rats by intermittent fasting. J Nutr. 1946 Mar;31:363-75.

Harvie M, Wright C, Pegington M, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013 Oct;110(8):1534-47.

Hildebrandt, Exercise attenuates the fasting-induce transcriptional activation of metabolic genes in skeletal muscle. Am J Physiol Metab 278:E1078-E1086, 2000.7.

Mattson, M. P. and Wan, R. Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. J Nutr Biochem. 2005 Mar;16(3):129-3

Pilegaard, H., et al. Effect of short-term fasting and refeeding on transcriptional regulation of metabolic genes in human skeletal muscle. Diabetes 52:657-662, 2003.

Stote, K. S., et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr 85:981-988, 2007.

Trabelsi, K., et al. Effects of Ramadan fasting on biochemical and anthropometric parameters in physically active men. Asian Journal of Sports Medicine 2(3):134-144, 2011.



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