Dr Jason Fung M.D. is a globally recognised Nephrologist (that’s a kidney specialist, for those of you who didn’t take ‘Doctor Naming 101’) and intermittent fasting expert. He is the author of The Obesity Code, and The Complete Guide to Fasting. And he’s taken literally thousands of people through his own intermittent fasting protocol, with awesomesauce results. On top of all that, he has a knack for explaining fancy-pants science and occasionally mind-melting medicine to regular Everyday Emmas like us. He even has his own fan club. Of which we’re loud and proud members!
Here, Dr Fung explains that we have worshipped at the altar of traditional calorie restriction far too long. It’s time to topple this false weight loss idol and replace it with something that actually, y’know, works! Now we know that intermittent fasting is the bee’s knees. But, did you know that it’s actually a lot more powerful than you realised? Read on to get the low-down on why intermittent fasting tops calorie restriction, hands down.
“Perhaps one of the most common questions we get is what the difference is between calorie restriction and fasting. Many calorie enthusiasts say that fasting works, but only because it restricts calories. In essence, they are saying that only the average matters, not the frequency. But, of course, the truth is nothing of its kind. So, let’s deal with this thorny problem.
Average calories versus eating frequency
The weather in Death Valley, California should be perfect with a yearly average temperature is 25 Celsius. Yet, most residents would hardly call the temperature idyllic. Summers are scorching hot, and winters are uncomfortably cold.
You can easily drown crossing a river that, on average, is only two feet (60cm) deep. If most of the river is one foot (30cm) deep and one section is ten feet (3 metres) deep, then you will not safely cross. Jumping off a one-foot wall 1000 times is far different than jumping off a 1000-foot wall once.
In a week’s weather, there is a huge difference between having seven grey, drizzling days with one inch of rain each and having six sunny, glorious days with one day of heavy thunderstorms and showers.
It’s obvious in all these examples that overall averages only tell one part of the tale, and often, understanding frequency is paramount. So why would we assume that reducing 300 calories per day over one week is the same as reducing 2100 calories over a single day? The difference between the two is the knife-edge between success and failure.
The calorie restriction approach
The portion control strategy of constant caloric reduction is the most common dietary approach recommended by nutritional authorities for both weight loss and type 2 diabetes. Advocates suggest that reducing daily calorie consumption by 500 calories will trigger weight loss of approximately one pound of fat (0.45kg) per week.
The American Diabetes Association’s main dietary recommendation suggests to “focus on diet, physical activity, and behavioral strategies to achieve a 500–750 kcal/day energy deficit.” The ‘portion control’ advice has been fairly standard since the 1970s, meaning that you should spread out the caloric reduction consistently throughout the day, rather than all at once. Dieticians often counsel patients to eat four, five or six times a day rather than skipping entire meals. To make it easier, there are calorie labels on restaurant meals, packaged food, and beverages. There are charts for calorie counting, calorie counting apps, and hundreds of calorie-counting books. Despite all this, success is as rare as humility in a grizzly bear.
After all, who hasn’t tried to portion control strategy? Does it work? Just about never. If you’ve tried it and failed, you’re not alone. Data from the United Kingdom indicates that this conventional diet advice succeeds in 1 in 210 obese men and 1 in 124 obese women. That is a failure rate of 99.5%, and that number is even worse for morbid obesity. So, whatever else you may believe, the constant caloric reduction does NOT work. This is an empirically proven fact. Worse, it has also been proven in the bitter tears of a million believers.
But why doesn’t it work? Beause of metabolic slowdown.
Calorie reduction forces the body to shut down in order to match the lowered caloric intake. Once expenditure drops below intake, you start the even more familiar weight regain. Ba-Bam! Weight is regained despite dietary compliance with the caloric restriction, even as your friends and family silently accuse you of cheating on your diet. Even after six years, the metabolic rate does not recover.
All of this is completely predictable. This metabolic slowdown in response to constant calorie restriction has been scientifically proven for over 50 years. In the 1950s Dr. Ancel Key’s famous Minnesota Starvation Study placed volunteers on a ‘semi-starvation’ diet of 1500 calories per day. This represented a 30% caloric reduction from their previous diet. In response, their basal metabolic rate dropped about 30%. They felt cold, tired, and hungry. When they resumed their typical diet, all their weight came right back.
Caloric restriction diets only work in the short-term, before basal metabolism falls in response. This is sometimes called ‘starvation mode’. Daily calorie restriction fails because it unerringly puts you into metabolic slowdown. It’s a guarantee.
Maintaining your metabolism
The secret to long-term weight loss is to maintain your basal metabolism. What doesn’t put you into starvation mode? Actual starvation! I’m kidding! What I’m talking about, of course, is the controlled version: intermittent fasting.
Intermittent fasting triggers numerous hormonal adaptations that do NOT happen with simple caloric reduction. Insulin drops but noradrenalin rises, keeping metabolism high. Growth hormone also rises, maintaining lean (muscle) mass.
Studies show that four days of continuous fasting does not drop basal metabolic rates. Rather, it increased by 12%. Why does this happen? Imagine we are cavemen. It’s winter and food is scarce. If our bodies go into ‘starvation mode’, then we would become lethargic, with no energy to go out and find food. Each day the situation gets worse and eventually we die. Nice. The human species would have become extinct long ago if our bodies slow down each time we didn’t eat for a few hours.
No, instead, during intermittent fasting, the body opens up its ample supply of stored food — body fat! Yeah! Basal metabolism stays high, and instead we change fuel sources from food, to stored food (or body fat). Now we have enough energy to go out and hunt some woolly mammoth.
During intermittent fasting, we first burn glycogen stored in the liver. When that is finished, we use body fat. Oh, hey, good news — there’s plenty of fat stored here. Burn, baby burn. Since there is plenty of fuel, there is no reason for basal metabolism to drop. And that’s the difference between long-term weight loss, and a lifetime of despair. That’s the knife-edge between success and failure.
Intermittent fasting is effective where simple calorie reduction is not. What is the difference? Obesity is a hormonal imbalance, not a caloric imbalance. The beneficial hormonal changes that happen during intermittent fasting are entirely prevented by the constant intake of food. It is the intermittency of the fasting that makes it so much more effective.
Intermittent Fasting vs Calorie Restriction
It is the intermittency of the diet that makes it effective. Studies have directly compared zero-calorie alternate-day fasting (ADF) and daily caloric restriction in obese adults. The Caloric Reduction (CR) strategy was designed to subtract 400 calories per day from the estimated energy requirements of participants. The ADF group ate normally on eating days, but ate zero calories every other day. The study lasted 24 weeks.
What were the conclusions? First, the most important conclusion was that this was a safe and effective therapy that anybody could reasonably follow. In terms of weight lost, fasting did better, but only marginally. This is consistent with most studies, where, in the short term, any decent diet produces weight loss. However, the devil is in the details. The truncal fat loss, which reflects the more dangerous visceral fat (the fat that wraps around the major organs like the liver, pancreas and kidneys), was almost twice as good with intermittent fasting as opposed to Calorie Reduction. In fat mass percentage, there is almost six times the amount of loss of fat using fasting!
Maintaining Muscle Mass
The other big concern is that intermittent fasting will ‘burn muscle’. Some opponents claim (without any evidence) that you lose a quarter pound of muscle (0.11kg) for every single day of fasting you do. Considering I fast at least 2 days a week, and have done so for years, I estimate my muscle percentage should be just about zero, and I shouldn’t even have enough muscle to type these words. It’s funny how that didn’t happen. But anyway, what happened in that study? The Calorie Reduction group lost statistically significant amounts of lean mass, but not the intermittent fasting group. Yes, there is LESS lean muscle loss. Maybe it has to do with all the growth hormone and noradrenalin being pumped out.
What happens to RMR, because that’s what determines long-term success? Using Calorie Reduction, basal metabolism dropped significantly by 76 calories per day, whereas the fasting group had no statistically significant drop. In other words, daily caloric reduction causes metabolic slowdown but fasting does not! So much for that old argument that ‘fasting puts you into starvation mode’.
What does this mean for Intermittent Fasting vs Calorie Restriction?
Fasting has been used throughout human history as a tremendously effective method of controlling obesity. By contrast, the portion control strategy of daily calorie restriction has only been recommended for the last fifty years with spectacular failure. Yet, conventional advice to reduce a few calories every day persists and intermittent fasting is continually belittled as an outdated, dangerous practice akin to blood-letting and voodoo. The study reports that “Importantly, ADF was not associated with an increased risk for weight regain”. Holy shiitake mushrooms. That’s the Holy Grail! The whole problem of obesity, calorie restriction is WEIGHT REGAIN, not initial weight loss. It’s relatively easy to lose weight. It’s hard to keep it off.
Weight regain differed during intermittent fasting vs calorie restriction. The fasting group tended to regain lean mass and continue to lose fat, while calorie reduction group gained both fat and lean mass. Part of the issue was that the intermittent fasting group reported that they often continued to fast even after the study was done. Of course! It is easier than they thought, with better results. Only a fool would stop! One of the very fascinating things is that ghrelin (the hunger hormone) goes up with calorie restriction but does NOT during intermittent fasting. We’ve known forever that dieting makes you hungrier. It’s not a matter of willpower — it’s a hormonal fact of life — the ghrelin goes up and you are hungrier. However, intermittent fasting does not increase hunger. Fascinating. No wonder it’s easier to keep the weight off! You’re less hungry.
The bottom line
Calorie restriction diets ignore the biological principle of homeostasis — the body’s ability to adapt to changing environments. Your eyes adjust whether you are in a dark room or bright sunlight. Your ears adjust if you are in a loud airport or a quiet house.
The same applies to weight loss. Your body adapts to a constant diet by slowing metabolism. Successful dieting requires an intermittent strategy, not a constant one. Restricting some foods all the time (portion control) differs from restricting all foods some of the time (intermittent fasting). This is the crucial difference between failure and success.
So here are your choices:
- Calorie Reduction: less weight loss (bad), more lean mass loss (bad), less visceral fat loss (bad), harder to keep weight off (bad), hungrier (bad), higher insulin (bad), more insulin resistance (bad), perfect track record over 50 years unblemished by success (bad!)
- Intermittent Fasting: More weight loss, more lean mass gain, more visceral fat loss, less hunger, been used throughout human history, lower insulin, less insulin resistance.
Almost every medical society, doctor, dietician and mainstream media will tell you to use choice #1. I prefer to tell people to take choice #2.
Dr Jason Fung M.D. is a world-leading expert on intermittent fasting. His passion for weight management and nutrition shines through in everything he does. To read more of his consistently insightful, always entertaining, and elegantly crafted work stay tuned! Make sure you check out his website idmprogram.com and books The Obesity Code and The Complete Guide To Fasting.