Chapter 2

Why Do Intermittent Fasting?

I’ve been following sound exercise and nutrition practices for nearly 20 years. That’s not just hot air either. I’m an evidence-based guy, and so of course, I have all the evidence to prove it.

Prior to my fasting experiments, I did a bunch of tests. Here are the results:

  • Age:
    37 years
  • Height:
    5’9”
  • Weight:
    190 pounds
  • Body Fat:
    10%
  • Bench Press:
    350 pounds for 1 repetition
  • Deadlift:
    450 pounds for 1 repetition
  • 40-yard Sprint:
    4.9 seconds
  • Vertical Jump:
    32 inches
Blood Marker My Value Reference Range
Glucose 5.0 mmol/L 3.6 – 6.0
Creatinine 103 umol/L 62 – 115
eGFR 72 mL/min/1.73 m2 60 – 89
AST 34 U/L 7 – 37
Cholesterol 3.78 mmol/L <5.0
LDL 2.24 mmol/L <3.36
HDL 1.15 mmol/L >1.04
Cholesterol/HDL 3.3 <4
Triglycerides 0.86 mmol/L <1.69
Hemoglobin 154 g/L 135 – 175
WBC 4.3 x E9/L 4 – 11
RBC 4.95 x E12/L 4.5 – 6.0
MCV 87.1 fL 80 – 100
MCH 31.1 pg 27.5 – 33.0
MCHC 357 g/L 305 – 360
RDW 12.2 % 11.5 – 14.5
NEUTS 1.3 x E9/L 2.0 – 7.5
LYMPH 2.2 x E9/L 1.0 – 3.5
MONO 0.6 x E9/L 0.2 – 1.0
EOS 0.2 x E9/L 0 – 0.5
BASO 0 x E9/L 0 – 0.2
Platelet Count 169 x E9/L 150 – 400
GGT 10 U/L 15 – 73
Thyrotropin 1.62 mIU/L 0.35 – 5
Testosterone 28.9 nmol/L 8.4 – 28.7

As you can see, for a guy nearing 40, I started this experiment lean, strong, fit, and muscular, and with a good blood profile that any doc would be satisfied with (notice all the values are within the reference ranges). I’m very happy with that. And for the record, I didn’t “train” for the pre-testing. This is just me. I’ve been able to maintain this kind of health and fitness profile, plus or minus 10 pounds of bodyweight, for nearly 20 years.

So why change anything?

I was curious. After my first one-day fasting experiment, some colleagues asked if I’d ever done any extended fasting experiments. I hadn’t. But I had become very interested in the work of strong IF proponents like Ori Hefenkler, Brad Pilon, and Martin Berkhan.

Reading the anecdotes from their website followers, I became intrigued with the idea that you could skip meals – and sometimes entire days of eating – without suffering lethargy, brain fog, and muscle loss. Even more intriguing was the idea that you could accelerate body fat loss and get healthier with strategic, well-timed fasts.

These claims run counter to today’s popular nutritional recommendations, which assert that small, frequent eating – grazing, if you will – is the best way to control appetite, blood sugar, and body weight.

As someone who’s averaged 4 to 7 meals per day for nearly 20 years, I was skeptical at first.

After all, the grazing concept has not only served me well, it’s helped over 100,000 of my own clients and readers (and millions of people worldwide) get into better shape. Especially in light of the infancy of the IF research, ignoring all the evidence and experience I have with grazing and higher meal frequency diets – or throwing it out the window based on the theories and anecdotes of a few individuals – would be an absurd overreaction.

Instead, I wanted to test it out myself. Precision Nutrition is itself a sort of private nutrition research firm: in search of the fastest and easiest way to lifelong fitness, we'll give any and all reasonable nutrition protocols a try.

Testing IF is a natural fit; we're always experimenting, and we're lucky enough to have a very large client base and data set to work with. I wanted some personal experience with IF before setting up a pilot study with a small group of clients. The only way to truly understand a nutritional system is to try it; in the fields of health and nutrition, the published research is always limited. (More on this later.)

So, my first reason for trying IF was a mixture of scientific and personal curiosity.

The other, more compelling reason? I had a new goal.

With the big 4-0 approaching, one of my “old man” goals is to compete in track and field at the master’s level – in particular, 100 m and 200 m sprint races. (I was a sprinter “back in the day” and thought it’d be fun to get started again.)

However, I know my body well. At 190 pounds, I was too heavy and slow. So, I decided to drop my body weight to a more track-friendly 170-175 pounds, which seems to be my sweet spot. To accomplish this, I set out the following goals:

Lose 20 pounds.

At 190 lb, I was just too big for my new goal of track and field competition. In sprinting, every pound counts. Although I was already lean, I needed to lose between 15-20 pounds to support my training.

Lose body fat.

Of course, I didn’t want to lose much muscle. Since I started this adventure weighing a lean 190 pounds, I knew that would be tough. I’d need to proceed cautiously in order to achieve a fit, healthy, high-energy, and absolutely ripped 170-175 pounds.

Stay lean.

In the past, I’ve been able to get extremely lean through more conventional dieting strategies. But only for so long. A bad mood and even worse food cravings would drive me to eat ravenously once the diet ended. This rebound eating brought me right back up to 190 pounds in short order. This time, I wanted to lose those last few pounds of fat and stay super lean... indefinitely.

Feel good.

My past diets made me cranky, miserable, and low in energy. Even though I looked great, I was mean. Plus, I didn’t think very well. (Again, all of this can be explained scientifically.) To keep Mrs. Berardi and my friends from punching me in the face, and to keep Dr. Berardi from turning into Mr. Hyde, my diets would normally have an “end date.” I didn’t want an “end date” anymore. I wanted to find a way to eat that would help me maintain my new body weight and conditioning while feeling great… forever.

Stay healthy.

I get my blood work done annually and all my values are in the healthy range, including my hormones. I wanted them to stay that way throughout the weight loss process. While properly losing weight helps with things like blood glucose and cholesterol, various hormones can get out of whack, negatively affecting health. So I wanted to make sure that all my blood values were in a healthy range even while dropping fat.

Although these are all reasonable goals individually, together they’re a pretty tall order for a guy who’s maintained his weight around 190 pounds for two decades. Although I could do it with a new training plan and a more conventional fat-loss type diet such as my very popular, and effective, "Get Shredded Diet" (see Resources), I wanted to put IF to the test. Could IF live up to the hype under these tough conditions?

Honestly, almost any basic exercise and eating plan can help a beginner and/or significantly over-fat person drop some weight. But it takes a pretty exceptional plan to help someone who’s already lean and muscular get down into the lowest range of body fat – without wrecking their performance or causing a massive rebound in body weight.

I was up for the challenge.