Does caloric restriction cause weight loss? Not according to science!


Worst advice ever?

There are many people, highly educated and believing themselves intelligent, that say that all diets come down to calories. So, any diet that works automatically comes down to cutting calories. It seems to be a fallback position of many academics and researchers and others who tend not to live in the real world. They say ‘This diet (Paleo, Low Carb, Whole Food etc.) works because it creates a ‘caloric deficit’. That is, reducing the calories you eat will create a caloric deficit. They often invoke the old Calories In Calories Out rule.

CRaP3-1024×853Change in Body Fat = Calorie Intake – Calorie Output. Yes. This is true. This is, of course, analogous to the crowded bar. Change in Bar Crowd = People In – People Out. But so what? Who cares?

The first law of Thermodynamics is always true, but completely irrelevant to human health. Yes, if Calories In is more than Calories Out then you will gain fat. But if you eat more calories, you will burn more calories. If you eat less calories, you will burn less. So there is no overall change in body fatness. Just like the bar – if more people come in, but more people leave, then there is no change.

The main caveat

The problem is that people now make the entirely unwarranted assumption that Calorie Output remains stable so that reducing calories intake (food) automatically results in loss of body fat. This is why I see tables like this, that are liked by so many. As I’ve written about many times, this is utterly false. Basal metabolism may increase or decrease up to 40%.

But this false belief results in the strategy that I call Caloric Reduction as Primary (CRaP). So many people believe that simply reducing calorie intake is a reasonable strategy of weight loss. They think that hormonal changes (mostly insulin and insulin resistance) created by intermittent fasting or paleo or ketogenic diets are irrelevant. For them, it’s all about calorie intake. But, we believe in evidence based medicine. So, where is the evidence that reducing calorie intake as the primary strategy results in long term meaningful weight loss?

People assume that it is a scientifically proven fact that reducing ‘Calories In’ will cause long term body fat loss. Experimentally, this is simple. Take some people. Randomize them. Give some of them calorie restriction. Watch them lose weight and live happily ever after. The others who continue with their usual diet don’t lose weight. Simple.

CRaP1Can somebody please point out those studies to me? We’ve recommended the ‘Eat Less, Move More’ strategy for almost half a century. Where are all these studies? Oh, right. They all conclusively show that CRaP does NOT produce long term weight loss. Let’s look at some of these studies. Especially the randomized controlled ones.

The TODAY study was a study of diabetics using medication (metformin) with or without lifestyle changes. This was primarily the calorie-deficit approach so beloved by academic physicians. The main study showed that this CRaP method produced no clinical benefits in diabetes management. What about weight loss?

Let’s see. At the beginning of the study, the average Body Mass Index of the lifestyle group was 34. After 5 years of dietary counselling to reduce calories, the average BMI was… 34. Nice job, guys. Glad you spent the last five years of your life counting calories?

CRaP2The Diabetes Prevention Program was another randomized lifestyle study that aimed to prevent diabetes, which was, in fact successful. But the question here is about weight loss.

With intensive counselling to reduce intake of calories weight loss was terrific (7 kg – 15 lbs). At first. In the long term, not so much. In a pattern familiar to every person who has ever dieted, the weight starts to regain despite continued compliance to the diet. Within a few years, there is only a small difference in weight (2 kg or less than 5 pounds) and by the end of the study, there is virtually no difference.

Body weight decreases nicely within the first 6-12 months, but thereafter shows steady weight regain.

The Women’s Health Initiative study

WHS-IWhat about non-diabetics? Let’s look at the Women’s Health Initiative. Almost 50,000 women were randomized into the trial and given instructions to reduce their fat intake. This is the largest and most important nutrition study ever done of the low fat caloric restriction diet intervention.

Over 7 years, women reduced their daily calorie intake by 361 calories per day. They reduced their percentage of calories from fat and increased their carbs. They also increased their daily exercise by 10%

Sounds like they followed the ‘Eat Less, Move More’ advice to a tee. So they must have lost lots of weight and thanked their academic doctors profusely as they slipped into their skin-tight yoga pants.

WHS-3Yeah, not really. Here’s what happened to weight loss. Against the comparison group that followed their usual diet, there was an initial weight loss, followed by the now familiar weight plateau and then eventual regain. There were no improvements in waist circumference either.

There are many who complain that this was not specifically a weight loss study. It’s always easy to nitpick study design after the fact. But the fact remains that two groups were randomized. One received dietary counselling to reduce calories, specifically from fat. As a result, calories were reduced. Isn’t it all about calories?

Let’s also use a little common sense here. Is this WHI result so unbelievable? Hundreds of millions of people have followed a calorie reduced diet. I certainly have tried it. What’s our personal experience? Pretty much exactly like the WHI study proved.

Also, it is important to note that women did, in fact, stick to their calorie reduced diet. Yet the weight regain still happened. BUT it wasn’t because of non compliance. This is often ignored, because physicians giving the dietary advice want desperately to believe that people fail on their diets because they didn’t follow it. They simply cannot face the super-obvious but highly inconvenient truth staring them in the face. If these women followed the diet, but still failed to lose weight – the problem is the DIET, and not the PATIENT. Doctors cannot play their favourite game of ‘Blame the Victim’.

So, every single diet works by reducing calorie intake, right? But every single study of reducing calorie intake shows no benefit in weight loss. How does that work? Where is this magical fairyland where reducing caloric intake automatically causes long term weight loss? How can all diets be successful only to the extent that they reduce caloric intake, when reducing caloric intake is proven to NOT cause weight loss?

We profess to live in an age of evidence-based medicine. But this only seems to apply to everything that is not the accepted conventional wisdom. The status quo always gets a free pass. Where is the evidence that cutting calories causes weight loss? Bueller? Bueller?

Jason Fung


A better way

How to Lose Weight

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Top videos with Dr. Fung

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Earlier with Dr. Jason Fung

Why Red Meat Won’t Kill You

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Dr. Fung has his own blog at He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code

His new book, The Complete Guide to Fasting is also available on Amazon.



  1. Hans
    Dr. Fung:
    "The problem is that people now make the entirely unwarranted assumption that Calorie Output remains stable so that reducing calories intake (food) automatically results in loss of body fat. "
    "Can somebody please point out those studies to me? "

    Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial.

    very low-calorie diet (890 kcal/d until 15% weight reduction, followed by a weight maintenance diet)

    After adjustment for changes in body composition, sedentary 24-hour energy expenditure was unchanged in controls, but decreased in the calorie restriction (-135 kcal/d [42 kcal/d]), calorie restriction with exercise (-117 kcal/d [52 kcal/d]), and very low-calorie diet (-125 kcal/d [35 kcal/d]) groups (all P<.008). These "metabolic adaptations" (~ 6% more than expected based on loss of metabolic mass) were statistically different from controls (P<.05).


    Dr. Fung
    "Women’s Health Initiative[...]is is the largest and most important nutrition study ever done of the low fat caloric restriction diet intervention."

    The Women's Health Initiative Dietary Modification Trial
    Interventions [...] did not include weight loss or caloric restriction goals.


  2. Vicente
    "Short-term: just eat less of anything and lose weight (including Twinkie diet).

    Long-term: all about WHAT you eat, not HOW MUCH"

    Ted Naiman

  3. Christine
    4 months keto diet with 18 hr intermittent fasting. No weight loss. Thought this would do it.
  4. Douglas Bughyut (M.D)
    You are an idiot. Calorie restriction is proven to work. You burn fewer calories when you eat less but you're still in a net deficit.

    Basal metabolism will fluctuate obviously but that's a given. If I gain 100lbs my BMR will increase automatically.

    The women did go over their calories, you're body cannot store energy unless the energy is supplied. And in multiple studies, they've shown that when you starve yourself purposefully you will eat and your brain will make you forget it happened to save you.

    Because in the holocaust only at around 1500 calories and they consistently lost weight and never regained it back even if they were in a camp for a very long period of time.

    Reply: #5
  5. Dr. Andreas Eenfeldt, MD Team Diet Doctor
    Starting your comment with "you're an idiot", and then bringing the holocaust into a discussion about weight loss? That unfortunately does not give confidence in your ability to reason scientifically. Calm down and try again.
  6. david
    the concentration camp example is a good one as it shows that calorie deprivation absolutely works for weight loss when compliance is assured, the only reason it fails is when people start eating more calories and no longer comply.

    But this simple point should not be needed to show that the above article is, of course, complete nonsense. There are millions of starving people around the world eating fewer calories than they need that are not fat at all, they get thinner and continue to stay lean, everybody knows this but many are so far down the fad diet logic rabbit hole that common sense is beyond them.

  7. Katie
    Nice propaganda for your position. I'm sure you have nothing to gain by claiming science is wrong. I'll tell you what - why not publish a science journal and get it peer reviewed if you have evidence that calorie restriction doesn't work? You'd win a noble prize rather just be a blogger. Go for it if you know you're right.
  8. Nate
    lol it seems like these studies/scientists aren't the ones providing the food... they're just telling them not to eat as many calories.

    These studies probably honestly show one thing... people lie about their dieting.

  9. Matt
    So are you saying the other fad diets that work don't have a calorie restriction? You said the chart and description is utterly false. So does that mean they are eating at maintance levels of calories or at a surplus of calories? BMR may increase or decrease up to 40% you say. So when you say that are you also talking about weight fluctuations or a 5'10" 180 lbs. man can fluctuate 40% BMR without any other factors involved besides diet? Because if so I would love to see your citation on this. Obviously people need to realize there TDEE is not stable and as they lose weight and also have had a constant calorie restriction they should constantly stay vigilant to maintain a deficit/maintainance.
  10. David
    Evidence: I used to be 220 pounds. I'm now 150 pounds.

    How I did it:

    (Wait for it)

    I ate less.™

  11. Antonis
    There's a response to this article here:
  12. Jade
    I'm sorry, this is ridiculous. I weighed 240 pounds in March of 2017 and now in March of 2019 I weigh 136 pounds, you know what I did? I counted my freaking calories (making sure to make most of them healthy calories, I realized I could eat a lot more protein and veggies and be fuller longer and have more energy than if I ate ice cream and bread) and exercised, even if that just meant I did 10,000 steps that day because I wasn't able to fit a real workout in.
    I am evidence that caloric restriction works and you cannot tell me otherwise, I am obviously no longer 240 lbs. Yes, you have to continue to reduce caloric intake in steps since your body progressively requires less and less calories to operate but that doesn't mean caloric restriction doesn't work.
  13. 1 comment removed
  14. Alex
    This article is nonsense. I weighed 105 kg last November 2018, BMI 31, and now, in June 2019 I weigh 75 kg and still losing weight consistently through calorie restriction and fitness.
    When overweight I was insulin resistant, hyperinsulimic, had thyroid deficiency and all the metabolic syndrome symptoms. I was in a rehabilitation clinic for burnout for 4 weeks as I started the weight loss journey under medical supervision.
    With calorie restriction and sports I reversed in just 4 weeks all my blood levels from borderline red flag to perfectly healthy while losing 6 kg.
    In the following months I continued to sustain and even improve lifestyle changes while going back to the high stress job and I kept losing weight and improving my body composition dramatically. I am now fully insulin sensitive, thyroid is working perfect, my metabolism is kept high through increased muscle mass from weight and cardio training.
    How do I do it? I weigh by the gram, cook it myself and log every single meal. It takes less than 5 minutes a day but it's a simple and effective method. I commute by lots of walking, play badminton 2x a week, go for a run or a walk every weekend and move my bum more often. I use the job lunch break for a walk every day. I weigh myself every morning and log my weight to correlate results with calorie intake. This is about as scientific as you can get.
    How do I restrict calories? Simple. At 105 kg my BMR was circa 2200 kcal. I starting losing weight by reducing my calorie intake from 2800 kcal (Which made me obese in the first place) to 1700 kcal a day. That is a lot of food if you eat properly. 3 meals a day with lots of water (30 ml per kg body mass) and 1 or 2 small fruit snacks. I even have deserts every now and then but home made so I control what and how much.
    After losing 30kg my BMR dropped to about 1800 kcal so to continue losing weight I now eat 1300-1400 kcal a day while being active. Smaller portions, cutting back on snacks and choosing less calorie dense foods. For every lost kg I reduce my calorie intake gradually by 10 kcal a day. That's such a small change I haven't even noticed when I dropped from 1700 to 1300 kcal. I plan to continue losing weight up to 68 kg which for my height is a healthy BMI of 24 or so and then maintain. I plan to keep logging food intake and tracking exercise as part of my lifestyle. I plan to keep checking the scale daily to avoid weight creeping back. I will probably have to restrict my calorie intake up to 1250 kcal for those last kilograms of fat to melt and then I plan to do maintenance by sustaining a body lean mass of at least 35-38% and increasing calorie intake gradually until the weight stabilized at 68 kg. I estimate this will be around 1500-1600 kcal. Folks, this is a normal food intake for a woman. My metabolism is not slowing down. I was pigging out before and calorie awareness works.
    Reply: #15
  15. Gentiann
    Your metabolism has been slowing down if you have to reduce your calories from 1700 to 1250 in order to lose weight.

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