Intermittent fasting has gained a lot of attention in the past few years. Maybe a little too much attention, but we'll see.

Is it the 'be all end all', the cure for your diet struggles, broken hormones, struggles to cut fat? 

No. It just isn't. However, it makes eating the right amount of food easier, plus - as you'll see - it takes advantage of some timing when it comes to your hormones to fuel your muscle and force fat loss.

The following excerpt is from my book, The Man Diet, with a few edits to cut down the length. 

From the Man Diet: Intermittent Fasting for Testosterone

We all naturally have the ability to train our body to use our own body fat for energy rather. And by practicing Intermittent Fasting regularly, your body can become more efficient at “flipping” this metabolic switch. When this switch is flipped, your body’s energy source changes from glucose to free-fatty acids, made from your own body fat, and ketones, which serve to preserve muscle.

When your body’s metabolic switch gets activated, the lipids in your adipocytes (fat cells) are then metabolized to free fatty acids, which are released into the blood. Simultaneously, other cell types may also begin generating ketones, with astrocytes in the brain being one notable example. After reading this, you are likely wondering how you can activate your metabolic switch.

Well, the good news is that this switch is likely turned on when you wake up every morning (or shortly thereafter), since this switch typically occurs after 8-12 hours of not eating. We’ve briefly covered a number of benefits that an IF approach can bring, such as reduced glucose levels in the blood, increased insulin sensitivity (incredibly important in maintaining an efficient body), and increases in growth hormone levels that lead to both improved fat loss and reduced aging.

But the benefits don’t stop there…

Intermittent Fasting will improve virtually every aspect of your health! In the section below, we review some of the benefits that are not widely known.

First, Intermittent fasting helps your cells become healthier, which can reduce toxic load. During fasting, the process that your cells use to eliminate waste products, called autophagy, is activated. This means you are cleaning out the “junk” when you are fasting, and this process appears to be critical to the survival of every cell in your body and has been linked to lifespan.

In fact, the Nobel prize was awarded to a researcher in 2016 for the discovery of autophagy and the connection between this cellular quality control process and virtually every aspect of our health. What’s more, the process of autophagy is actually required to maintain muscle mass. When autophagy was intentionally prevented in rodents, their muscles quickly atrophied and they became weak[A2]. This is actually not all that surprising when you think about it, since we know the importance of sleep to muscle growth, and for most people sleep is the time when autophagy is highest!

Findings such as this strongly suggest that any impairments in the cellular quality control system can accelerate the process of muscle degradation during aging! Not only that, but when this cellular quality control process is not functioning efficiently, your metabolism can actually slow down and set you up for unhealthy weight gain. For most people living an unhealthy lifestyle, this process unfortunately declines with age, and leads to increased abdominal fat and muscle loss [A3].

Once accumulated, this excess body fat can further disrupt cellular quality control processes and set up a vicious cycle of fat gain and muscle loss [A4]. On the other hand, when you practice Intermittent Fasting, your cells can become healthier. And healthier functioning cells means that there are less “bad guys” around, which allows your body to use more of its resources to repair and recover instead of fighting the “bad guys.” Now, efficiency is something we’ve also talked about briefly thus far in the Man Diet, and an IF approach to eating will help your body eliminate waste that can also help speed up the healing and recovery process. What’s more, science has now revealed yet another amazing benefit of short-term or intermittent fasting, which is that it can dramatically increase the supply and availability of particular types of stem cells, called mesenchymal stem/progenitor cells, which decline during aging[A5].

In practical terms, this means that Intermittent Fasting helps your tissues repair and recover by increasing the supply and availability of stem cells. In addition to the great benefits described above that occur at the cellular level, Intermittent Fasting has been shown to have broad systemic effects and trigger important biological pathways that promote health and optimize function.

Intermittent fasting regimens have consistently been found to decrease fasting glucose levels and reduce insulin resistance, as well as reduce both systolic and diastolic blood pressure and improve blood cholesterol levels. You may have heard of Insulin Resistance and how it can lead to type 2 diabetes. Well, the opposite of insulin resistance is insulin sensitive cells, and when you practice intermittent fasting regularly your cells become more insulin sensitive! During intermittent fasting, plasma glucose, insulin, and leptin levels all go down, and ketone and adiponectin (fat burning hormone) levels go up, reflecting the body’s switch in fuel source from glucose to fatty acids and fatty acid derived ketones.

In a recent study, serum ketone bodies were almost 4 times higher when individuals followed a fasting mimicking diet compared to their normal intake [A6]. During fasting, growth hormone go way up [A7]. And we know that increased growth hormone levels change energy substrate utilization by liberating free fatty acids, and using these for energy in preference of protein. In order words, the increase in growth hormone during fasting increases lipolysis (fat burning) and also helps preserve your lean muscle tissue. This is likely one of the key mechanisms through which Intermittent Fasting improves body composition, which we discuss in more detail shortly.

Fasting also increases your body’s glucagon. Glucagon is one of the dominant hormones in your body that’s responsible for burning fat. This gives you one more tool that will help you burn fat, positively affecting your testosterone levels at the same time. Not only that, glucagon is a critical hormone for increasing satiety (feeling full), which may be one reason that many people do not experience hunger when they fast for short time periods (14-16 hours).

This all sounds great, but is there any scientific evidence that Intermittent Fasting can work for men who lift weights? The answer is a resounding YES!

The findings of a clinical trial specifically conducted in men who practiced Intermittent Fasting and Weight Lifting are now available! In this study, 34 healthy men were randomly assigned to either a normal control diet or daily Intermittent Fasting (16 hours of daily fasting) and followed for two months during which they maintained a standard resistance training program, the men in the Intermittent Fasting Group showed a reduction in fat mass (compared to normal diet) but no loss of lean mass or maximal strength.(125)

Based on these findings, the scientists concluded “Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.” As great as these findings are, we believe you can do even better and pack on high quality muscle by taking advantage of the two anabolic windows that occur when you practice intermittent fasting with strength training. As we mentioned earlier, the first anabolic window occurs immediately following your 14-16 hour fast.

During this time, your body has utilized its glucose/glycogen supply and is burning fat for energy, which sets you up for a large anabolic response to your first meal. Ok, but what should I eat for my first meal?

Here, we recommend eating a meal comprised mostly of healthy fats with some protein and a small amount of carbohydrates… if your goal is to maximize fat loss and gain lean muscle. This type of meal will not only prolong the fat burning period, but also provide your body with a healthy supply of energy along with the building blocks it needs to grow and/ or maintain muscle. If you are less concerned about body fat, then you can be more liberal with the carbohydrate intake at this meal.

The pro is that an increase in carbohydrate intake at this time could amplify the anabolic response by stimulating the hormone insulin and thereby potentially increase muscle growth. On the other hand, too many carbohydrates at this time can take you out of the fat burning state and trigger a metabolic switch for fat storage. It all depends on your goals! The second anabolic window happens during the postworkout time period at night, presuming you train in the afternoon and/or early evening. After this workout, you get a huge insulin response at the time when your muscles are primed to absorb glucose to repair and regrow. So, during this post-workout anabolic window, almost all the glucose from carbohydrates is used by your muscles and does not stay in your bloodstream for long. You now have “free reign” on your post workout meals. That is, eat however many carbs and proteins as you want.

Keep your fats low, but pig out on your post workout meals. Keep the rest of your meals big, but high in fats and low in carbs. This will likely lead to a break in your macros, which, to be honest, is fine. If you’re going above and beyond with your carbs and protein in your post-workout meal, and your goal is to gain muscle, you’ll be fine. If your preference is to train in the morning, all is not lost. While you will not have two anabolic windows, your post-training anabolic window will be HUGE!

That is, if you have fasted and/or had only amino acids before your morning training session. If so, then the next meal you eat will be critical to your muscle building success and should primarily consist of liberal quantities of carbohydrates (both simple and complex) as well as some lean protein.

A Bit More Science

In order to gain a better understanding of the effects of Intermittent Fasting on changes in body composition, Dr. Anton and his research team completed a systematic review of findings of clinical trials that were conducted in the past few decades. (Anton et al. XY)

This article entitled Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting was most downloaded paper in 2017 from the journal Obesity and can be found here[A8] - https://www.ncbi.nlm.nih.gov/pubmed/29086496

In addition to the Moro study (described above), three of four eligible trials showed that the Intermittent Fasting approach recommended in The Man Diet significantly reduced body weight and body fat in both normal weight and overweight men (and women).

Importantly, no significant reductions in lean mass were reported in any study, which suggests the weight losses were primarily comprised of body fat. Equally important, the participants were NOT restricting calories during their eating window. Earlier we discussed how restricting your calorie intake can LOWER your T levels.

The good news is that by consistently practicing Intermittent Fasting, you get the fat loss benefits of calorie restriction, without the downside of LOWER T levels, as well as less lean mass, neither of which is good! For studies involving Alternate Day Modified Fasting or Alternate Day Fasting, significant reductions in body weight and fat mass were observed in 10 of the 10 eligible trials.

Yes, you read that correctly, 10 of 10 trials showed significant reductions in body fat.

Additionally, the magnitude of weight losses were quite large with almost all of these trials reporting substantial reductions in body weight (> 10 lbs). If you are a more visual person, the figure below summarizes the changes in body fat and lean mass that occurred follow studies using TRF and ADMF from Dr. Anton’s review.

So what does all this science mean for you?

Well, it means that a few things:

1) you have choices in the approach you take to Intermittent fasting, and

2) the type of program you choose should be based on both your goals and lifestyle preference.

The type of Intermittent Fasting approach we recommend of fasting for a window of 14-16 hours daily can clearly stimulate fat loss . And it can, actually be a great way to build muscle without gaining a bunch of fat like you’ll see in bulking approaches that actually have a negative eff ect on the muscle-building hormone, testosterone.

Additionally, it can produce amplify the release of growth hormone, which is known to have favorable effects on body composition. If your focus right now is strictly fat loss, however, and are as not as concerned about losing lean muscle, then the Alternate Day Modified Fasting approach would likely be your best strategy. With this approach, you would eat a very small meal (500 calories or less) during the afternoon one day, and then “feast” the next day.

The good news is that as long you first completed the “fast” day, you can go wild on the “feast” day and eat until your heart is content. The research is clear – you will indeed lose fat and relatively little muscle following this approach. It is, however, important that you do eat the small meal on your “fast” day. In the only study to look at the effects of Alternate Day Fasting (no calories at all on Fasting Days), the participants lost a significant amount of lean tissue (aka muscle)!

References:

[A2]Masiero E, Agatea L, Mammucari C et al. Autophagy is required to maintain muscle mass. Cell Metab 2009;10:507-515.

[A3]ingh R, Kaushik S, Wang Y et al. Autophagy regulates lipid metabolism. Nature 2009;458:1131-1135.

[A4]Verdejo HE, del CA, Troncoso R et al. Mitochondria, myocardial remodeling, and cardiovascular disease. Curr Hypertens Rep 2012;14:532-539.

[A5]Cell Metab. 2015 Jul 7;22(1):86-99. doi: 10.1016/j. cmet.2015.05.012. Epub 2015 Jun 18. The Man Diet 180 A Periodic Diet that Mimics Fasting Promotes MultiSystem Regeneration, Enhanced Cognitive Performance, and Healthspan. Brandhorst S1 , Choi IY1 , Wei M1 , Cheng CW1 , Sedrakyan S2 , Navarrete G1 , Dubeau L3 , Yap LP4 , Park R4 , Vinciguerra M5 , Di Biase S1 , Mirzaei H1 , Mirisola MG6 , Childress P7 , Ji L8 , Groshen S8 , Penna F9 , Odetti P10, Perin L2 , Conti PS4 , Ikeno Y11, Kennedy BK12, Cohen P1 , Morgan TE1 , Dorff TB13, Longo VD14.

[A6] See 1 citation: Cell Metab. 2015 Jul 7;22(1):86-99. doi: 10.1016/j. cmet.2015.05.012. Epub 2015 Jun 18. A Periodic Diet that Mimics Fasting Promotes MultiSystem Regeneration, Enhanced Cognitive Performance, and Healthspan. Brandhorst S1 , Choi IY1 , Wei M1 , Cheng CW1 , Sedrakyan S2 , Navarrete G1 , Dubeau L3 , Yap LP4 , Park R4 , Vinciguerra M5 , Di Biase S1 , Mirzaei H1 , Mirisola MG6 , Childress P7 , Ji L8 , Groshen S8 , Penna F9 , Odetti P10, Perin L2 , Conti PS4 , Ikeno Y11, Kennedy BK12, Cohen P1 , Morgan TE1 , Dorff TB13, Longo VD14

[A7]M.L. Hartman, J.D. Veldhuis, M.L. Johnson, M.M. Le, K.G.M.M. Alberti, E. Samojlik, M.O. Thorner, Augmented growth hormone (GH) secretory burst frequency and amplitude Your Simplified Schedule 181 mediate enhanced GH secretion during a two-day fast in normal men, J. Clin. Endocrinol. Metab. 74 (1992) 757–765

[A8]Obesity (Silver Spring). 2017 Oct 31. doi: 10.1002/ oby.22065. [Epub ahead of print] Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Anton SD1,2, Moehl K3 , Donahoo WT4 , Marosi K3 , Lee SA1,2, Mainous AG 3rd5,6, Leeuwenburgh C1,2, Mattson MP3,7