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  • Writer's pictureDoug Joachim

Fast (ing) Weight Loss: Intermittent Fasting

Updated: Jul 11, 2023

Until recently, I recommended my clients eat 5 to 6 small daily snacks/meals spaced evenly throughout the day to stoke their metabolism.  Most nutritionists and dieticians still cling to this maxim although the science on its effectiveness is quite sketchy.  It works for some people, for many others, not so much.  Grazing your way through the day on small meals consistently elevates your blood sugar, potentially promoting a better fat storage environment.  In turn, this guarantees your body will never have to utilize much fat for energy since there’s a constant supply of sugar in the bloodstream (thanks to that meal you ate 3 hours ago and are about to repeat).  Moreover, eating too often disrupts the leptin/ghrelin balance (hormones that control hunger) and may lead to leptin resistance, making it hard to feel sated.  It’s like having a hungry monster in your stomach that can’t get enough food.

Over the last 2 decades, I noticed something interesting:  most of my slim clients skipped breakfast and did not snack, but they stayed skinny.  Evidently, they were practicing a form of intermittent fasting (IF).  We all do it a little bit unless you are waking up in the middle of the night to eat.  It is quite simply a period of fasting followed by a period of eating.  Most IF programs recommend you fast for at least 14 hours or more a few times a week.  It has been shown to increase fat burning metabolism, protect the brain from disease and lower homeostatic blood glucose levels in nonhuman animals. There have been many animal studies (most using lab rats and monkeys), depicting the benefits of strategic fasting.  Sadly the scientific community has not completed any long-term human-controlled experiments studying the effects of intermittent fasting. Animal research is well done but we are not exactly rats or monkeys. However, the data we have is promising and copious amounts of anecdotal evidence report good success with strategic fasting diets.

Here are some more benefits that are seen in ‘other than human’ animal models:

  1. Reduced blood lipids

  2. Reduced blood pressure

  3. Reduced markers of inflammation

  4. Reduced oxidative stress

  5. Increase fat burning

  6. Increased growth hormone release later in the fast

  7. Increased metabolic rate

  8. Improved blood sugar control (by lowering blood glucose and increasing insulin sensitivity)

NOTE: New human RCT research published in 2020 showed no weight loss benefit to intermittent fasting.

While examining human evolutionary history, one might conclude that for most of our time on earth we’ve involuntarily participated in various forms of fasting diets, otherwise known as periodic starvation.  Our population unwillingly subsisted on the feast or famine meal plan.  And no early man ate cereal for breakfast…they simply skipped brunch altogether because the fridge was empty. Our great grandparents and their great grandparents did not have access to food 24/7 (many people on this planet still don’t).  In fact, if they had a craving for something, they had to get off their butts (actually, they probably weren’t sitting) hunt, kill then cook it from scratch!

The ability to “fast” for days on end lies within us all.  If you are reading this, you are the very lucky genetic end product of ancestors who were wily enough to survive during times of starvation.  Throughout periods of low food, it was survival of the fittest and fattest.  In fact, modern man continues to practice a type of IF every day.  It is common for most people to go half the day or more without food.  If you eat dinner at 8 PM and breakfast at 8 AM, you just fasted for 12 hours.  The human body is built to function efficiently without food.

Interestingly people and animals who fast for a full day usually make up the calories the next day or later in the week yet still reap the health benefits of a calorie-restricted diet including the weight loss part!  But why?  It seems that practicing IF increases: human growth hormone output (which burns fat and increases lean muscle), catecholamines which raise your metabolic rate while decreasing insulin levels and allowing stored fat to be burned for fuel.  Furthermore, the constant eating most of us engage in may lead to metabolic exhaustion. By practicing IF your body will eat up all your sugar stores within 6-8 hours and you will preferentially burn stored fat until you dine again. Yeah!

The method I find the least painful and still efficacious is the 16 hour fast (mostly done while sleeping) and 6 to 8 hour feeding period done 2 to 7 times per week.  Here is an example of how it works:

Eat your last meal of the day at 7 PM and then skip breakfast in the morning and dine on your first meal at 11 AM.  Yes, I said skip breakfast, the most important meal of the day…more on that later.  Eat regularly for the next 6 or 8 hours and at the end of this feeding time (sounds like something we do with zoo animals) fast until breakfast the next morning.  It is really not that hard.  Try this 2-3 day the first week and then gauge how you feel.  Tweak accordingly.

Intermittent Fasting Rules:

  1. Don’t eat for a period of 14 to 20 hours

  2. Drink lots of water

  3. For this to work (for better body composition) you must exercise regularly

  4. Drink non-sweetened tea or coffee (no milk or just a splash during fasting hours)

  5. Do not drink juice! It is full of sugar and will interrupt your fast

  6. Limit your eating window to 4-10 hours

  7. Do not drink alcohol during a fast

  8. Eat healthy foods during your feeding periods (lots of veggies, protein, and good fats)- not whatever you want – but bigger meals than normal.

If your mother raised you right she told you “breakfast is the most important meal of the day”.  Sorry mom, the research on this is quite skimpy (although school-aged children should eat breakfast due to the strong correlation between it and higher cognitive abilities).  Does eating breakfast prevent weight gain and decrease hunger?  I don’t know about you, but many times breakfast makes me hungry for more food.  Eat begets eat. Breakfast, specifically a carbohydrate-laden one, will spike your insulin (this is why your doc wants you to fast prior to blood tests) and shuts down all fat burning.  Going without breakfast seems to stoke the fat burning process.

In any event, try to develop a habit of going at least 12 hours without eating on a regular basis. This will give your metabolic processes a rest and teach you how to deal with a little hunger.  Being hungry for a few hours won’t kill you and might even feel good.  Embrace the feeling and 2x per week or preferably every day,  depending on your goals, go big and strive for a 16-18 hour fast.  Obviously, there are many people not suited for IF due to diseases like diabetes, anorexia and/or daily medications needed to be taken with food.  Before starting a program like this talk to your doctor or dietician about your options.  Experiment with what works best for you and your schedule and always remember to drink lots of water.


1. Journal of Nutritional BioChem: Beneficial Effects of Intermittent Fasting 2. Dr. M. Eades Nutritional Science  3. NY Times: Big Breakfast Bigger Daily Calorie Count 4. Free Book: Intermittent Fasting: Dr. John Berardi 5. An Objective Look-at-Intermittent-Fasting 6. Verboeket-van de Venne WP, Westerterp KR. Influence of the feeding frequency on nutrient utilization in man: consequences for energy metabolism. Eur J Clin Nutr. 1991 Mar;45(3):161-9. 7. Taylor MA, Garrow JS. Compared with nibbling, neither gorging nor a morning fast affect short-term energy balance in obese patients in a chamber calorimeter. Int J Obes Relat Metab Disord. 2001 Apr;25(4):519-28.

Doug Joachim – NYC personal trainer


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