Cutting calories won’t solve your weight issues – do this instead

Dieting habits changes. Woman hates vegetarian diet

Contrary to what most people believe, long-term weight loss is not simply about cutting a few calories here and there. Sure, it sounds like it works, but the bottom line is that for most people it does not. This has been proven in numerous studies and also the countless tears of unsuccessful dieters desperately counting their calories like Ebenezer Scrooge counting his pennies.

We pretend we live in a world where nutrition demands scientifically rigorous proof that prescribed treatments are effective. So, where are the studies that show that cutting calories causes long-term weight loss? After 50 years of desperate, intense research, guess how many studies prove its long-term effectiveness? How about zero? That’s right, Nada. Zilch. Zero.

The only reason we think the ‘caloric reduction as primary’ strategy is effective is because it’s been repeated so often. It’s like Santa Claus. When I was a kid, I thought “So, some random guy is just going to give me presents for no reason?” But repeated often enough, these tales gain an undeserved sheen of truth.

thermostat2No, I believe the key to successful weight loss is to control your body’s ‘thermostat’ – the body set weight (BSW). A room thermostat is set to your desired room temperature and in the summer, when the outside temperature is hot, it turns on the air conditioning. In the winter, it detects the temperature is too cold, and turns on the heat. Your house stays at the perfect temperature despite wildly varying outside conditions.

In our bodies, we have the BSW, also called an appestat or obesistat, essentially a thermostat for body fatness. Some people believe we are designed to eat everything in front of our face and now that food is so easily available, we have no choice but to gain weight. This completely ignores normal human physiology.

Instead, we have multiple overlapping powerful satiety mechanisms to stop eating. We have stretch receptors in our stomach to signal when it is too full. We have powerful satiety hormones such as peptide YY and cholecystokinin that stop us from eating. Think about a time you’ve eaten too much at a Chinese buffet. Would you be able to eat two more pork chops, just because they are available and free? Think about those restaurants that will give you a free meal if you can eat 40 oz of steak in 1 hour. Are they going bankrupt anytime soon? No. Because it is really, really hard to keep eating once we’re full. Yet these are the very same pork chops or steak that we hungrily ate just a few minutes ago, prior to the meal.

From an evolutionary standpoint, these satiety mechanisms make a lot of sense. Our body is designed to stay within certain body-fat parameters. If you are too skinny, you will die during the hard times (winter). If you are too fat, you will not be able to catch food, and you might just get eaten yourself. Wild animals almost never become obese to the point of being unable to function normally. Where are the morbidly obese antelope? Caribou? Lions? Tigers? Fish? When food is plentiful, numbers of animals increase. You don’t get a few morbidly obese rats. You get thousands of relatively normal-sized rats.


The body set weight

The BSW sets an ideal body fatness that it defends just like our house thermostat. If we are too skinny, we try to gain weight. If we are too fat, we try to lose weight.

The clearest experimental demonstration of this was done by Dr. Rudy Leibel in 1995. In this experiment he took volunteers, and overfed them to make them gain 10% more weight. Then he returned them to their regular weight, and then to 10% or 20% weight loss. At each point, he measured the basal metabolic rate (BMR), or how much energy (calories) the body is expending. After 10% weight gain, the body burns about 500 calories more per day compared to baseline. As the body returns to it’s original weight, so does the metabolic rate. After 10% weight loss, the body burns about 300 calories per day less.

The body tries very hard to maintain its BSW in the original position, acting just like our house thermostat. This directly contradicts the Calories In/ Calories Out (CICO) viewpoint that hold that simply eating too many calories causes body fatness without regard to the BSW or satiety hormones or pretty much any other physiologic signaling. If you deliberately overeat, your body tries to burn it off.

‘Calories’ is not a physiologic notion, as we’ve previously discussed. Our body has no ‘calorie’ receptors and does not know how many calories we eat or don’t eat. Over the past several centuries, we’ve decoded many of the human metabolic pathways. Do you see ‘calories’ mentioned ANYWHERE in this complex diagram?


A calorie of carbohydrate is metabolized entirely differently from fat or protein. So why pretend they are the same? It’s like saying that humans and a tree trunk share the same physiology because we both weigh the same and would produce the same heat if burned in a calorimeter. Believing this notion is a big part of why we’re losing the war on obesity.

This notion of ‘A calorie is a calorie’ is mostly pushed by processed-food companies trying to convince you that it is fine to swap 100 calories of avocado for Coke in terms of weight gain. For food companies, the calories model is like Santa Claus. As long as they keep people believing, its a gift that keeps on giving. They can sell sugary beverages and tell people with a straight face that 100 calories of sugar is as fattening as 100 calories of kale.

Why ‘caloric reduction as primary’ does not work

Suppose our house thermostat is set to 72F (22C) degrees, but we now want to be at 70F (21C). Ignoring the thermostat, we turn on the portable air conditioner in. At first, the temperature drops to 70F (21C) but then the thermostat turns up the heat to return the room to 72F (22C). We don’t like that, so we put a second and third air conditioner in. In response, the thermostat turns the heat on full blast. We continually fighting against ourselves in an ultimately futile attempt. Well, that didn’t work. What is a simpler solution? Turn down the thermostat.

This is analogous to reducing calories to lose weight because it completely ignores the BSW. Suppose our BSW is set at 200 pounds (91 kg), but we want to weigh 170 pounds (77 kg). Conventional advice tells us to cut 500 calories per day to lose 1 pound per week. Initially weight goes down to 185 pounds (84 kg), but then our appestat kicks in to make us gain weight. We become hungrier and basal metabolism slows in order to regain the weight. So we try even harder by cutting more calories. But our body responds by further slowing our metabolism. We continually fight against ourselves in an ultimately futile attempt to lose weight. Well, that didn’t work. What is a simpler solution? Turn down the appestat or BSW. How to do that? Read on, my friend.

The body weight ‘thermostat’

So how does our appestat work? Recall that excessive insulin continbutes to obesity in addition to excessive calories. It is a hormonal imbalance. If you are not familiar with these ideas, you can find details in The Obesity Code book or review my past blogs at If you need further help, you can contact us for personalized coaching or join our membership program. Insulin signals our body to store food energy in the form of body fat. When we fast, and insulin goes down, we burn some of that stored energy and this is why we don’t die in our sleep every night.


A thermostat works on a negative feedback loop. If the temperature is too low, the thermostat turns on the heat until it gets to the proper temperature and then it stops. The body also uses a negative feedback loop in the BSW. Excessive insulin leads an increase in the size of fat cells. They produce more of the hormone leptin which travels to the brain and signals that ‘we’re too fat’. Appetite decreases, we stop eating, and this lowers insulin. This signals our body to start burning fat instead of eating and storing it and returns us to our original, desired BSW.

This feedback loop keeps our weight relatively stable despite wide fluctuations in calorie intake and calorie expenditures day after day, week after week and year after year. After all, most people become obese by gaining 1-2 pounds (0.5-1 kg) per year. Over 40 years, this can add up. Assume that 1 pound (0.5 kg) of body fat is roughly 3500 calories. In a year, we might eat 2000 cal/day times 365 days = 730,000 calories. To gain 1 pound (0.5 kg) a year (3500 calories), we would need to accurately match calorie intake and expenditure to a 99.5% accuracy rate. That’s impossible. I have maintained an even weight since grade school, but I have no idea how many calories I eat and how many I expend. How do I maintain a 100% accuracy rate? Clearly, I could not do this through conscious regulation of my food intake/ exercise. No, body fat is regulated by a feedback mechanism – the BSW ‘thermostat’.

Obesity is therefore not just a caloric balance problem, but rather the gradual increase in the BSW thermostat (appestat) over time. Let see how that works.


The BSW is likely created by the balance of insulin effect versus leptin effect, just as the thermostat is regulated by the balance of heat versus cooling. In those who are obese, it is likely that the insulin effect has prevailed over leptin effect. For example, if we inject exogenous insulin, we gain fat because we have tilted the balance towards insulin. In normal human obesity, this could be due to a number of reasons, but eating foods high in refined grains, eating frequently, eating lots of sugar (causes hepatic insulin resistance directly) are all culprits in keeping insulin levels high despite leptin’s best efforts to curb appetite to lower insulin. If insulin is extremely low, as in type 1 diabetes, the body loses weight continuously no matter how many calories are eaten.

boxingThe battle royale for the BSW is Insulin vs. Leptin. One is trying to make us gain fat, the other is trying to lose fat. It’s Rocky vs. Apollo Creed. These two heavyweight hormones that control body fat percentage are trading body blows. If leptin wins, then we are able to reduce appetite and/ or increase basal metabolic rates sufficiently to burn off the excess calories being eaten. This is exactly what we saw in Rudy Leibel’s study of deliberate weight gain.

But obesity is commonly a disease caused by too much insulin – hyperinsulinemia. If you are obese, it may be because insulin prevailed over leptin. As the fat cells stay over-filled, they produce more and more leptin in an attempt to fight insulin. This should help in the Battle Royale. And it does, often for decades. However, the root problem of hyperinsulinemia has not been solved (eating too much sugar, too many refined carbohydrates, eating constantly), so insulin also continues to march higher. And persistent high levels of hormones result in resistance. Eventually, persistent, high levels of leptin cause leptin resistance. Persistent high levels of insulin cause insulin resistance. But just as true – persistent high leptin levels cause leptin resistance.


This leptin resistance is virtually universal in common obesity. With leptin down and out, insulin is now unopposed to cause weight gain. The insulin vs. leptin battle has been lost, and the BSW thermostat is reset upwards.

So, what’s the answer? Suppose we use the standard dietary advice of cutting dietary fat, reducing calories but eating lots of carbohydrates and eating 6 or 7 times per day. Since dietary fat has little insulin effect, this caloric-reduction strategy may not reduce the insulin effect and may make little difference to this Insulin vs. Leptin battle. The BSW can be unaffected and our bodies desperately try to regain the lost weight. This is precisely the dietary advice given over the last 40 years that has failed so spectacularly. Eating frequently means constant stimulation of insulin, which is also detrimental to weight loss efforts.

The key to combating obesity, then is to help in the Insulin vs. Leptin fight by lowering insulin. Everything depends upon it. Leptin is already maxed out. The only thing left is to lower insulin. How to do that? Well:

  1. Eat less sugar
  2. Eat less refined grains
  3. Eat adequate protein and fon’t avoid natural fats
  4. Don’t eat all the time (time restricted eating or intermittent fasting). Stop snacking
  5. Eat real unprocessed foods (lower in insulin effects)

Funny. That’s precisely the sort of no-nonsense advice your grandmother would have given. Low Carb Healthy Fats + Intermittent Fasting. Boom.

Dr. Jason Fung


Dr. Fung’s top posts about weight loss

  1. My single best weight loss tip
  2. "Do you have any suggestions to improve sleep when fasting?"
  3. What and when to eat to reduce insulin

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Dr. Fung


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

The Obesity CodeThe Complete Guide to Fasting

Dr. Fung’s books The Obesity Code and The Complete Guide to Fasting are available on Amazon.


  1. Simon
    Thanks Jason, I love your incremental work ever inching towards deducing the truth and debunking the "Sheep" bleating "Cico"s (pronounced "Psychos")
  2. Karen
    I’ve seen some people follow high fat, low carb diets with intermittent fasting, and still not lose weight. I think that because of the leptin resistance you mention above, they don’t know when they are full and when to stop eating. They add tons of cheese and high calorie comfort fats to meals. In these cases it seems like we do still need a daily caloric goal so they don’t overeat (even on protein or fats).... Aren’t we throwing the calorie baby out with the bath water?
    Replies: #5, #7
  3. Marianne Gray
    Excellent Dr.Fung!
  4. Mary S
    Dr Fung’s article clearly shows we can reduce insulin levels, but will leptin levels return to normal by eating low carb?
  5. Sharon Baker Burress
    I, too, believe that to be true. I have lost 155 lbs on a Ketogenic diet and lack 10 lbs of getting to my normal weight. Every time I increase my fat intake above 70 grams, I gain weight. I really would like to enjoy all these Keto fat-heavy recipes I see online, but when I do, I regain. I keep my carbs below 20 g net. My protein intake rarely varies.

    I’ve seen some people follow high fat, low carb diets with intermittent fasting, and still not lose weight. I think that because of the leptin resistance you mention above, they don’t know when they are full and when to stop eating. They add tons of cheese and high calorie comfort fats to meals. In these cases it seems like we do still need a daily caloric goal so they don’t overeat (even on protein or fats).... Aren’t we throwing the calorie baby out with the bath water?

  6. Sharon Baker Burress
    I would like to see Dr. Fung’s inclusion of glucagon in this formula.
  7. Terese
    It takes time for the body to sort this out. I wouldn't give up on the low carb healthy fat + intermittent fasting too early.
  8. Gün
    Keeping insulin levels low by eating low carb and doing intermittent fasting, all while also creating a calorie deficit results in (sustainable) weight loss. Just lowering insulin levels but eating more calories than one burns will certainly not lead to weight loss, but might even lead to weight gain if kept up over longer periods of time. I am totally on board with Dr. Fung - until the message is oversimplified into "calories don't matter at all". The more nuanced our messages are, the better equipped we can be to fight mainstream misconceptions about nutrition and weight loss!
  9. Stephen
    There is a difference in CICO and energy balance. Of course amount of calories matter... of course quality of food matters... of course hormones matter ... they all matter

    To say it is either calories or hormones is just dumb

  10. 1 comment removed
  11. Felicity Campbell-Smith
    For 3 years I have been doing the low carb high fat diet, only eating once a day, and have seen little change in my weight. Over those3 years I have lost 5kg why? Does anyone answer these questions?
    Reply: #13
  12. Ron
    The information may be faulty if you are not losing weight in over 3 years. I wish I could tell you, but I am stumped.
  13. Camilla
    Well, dont know if you're still hanging around here, but here's an attempt at troubleshooting. First, do you have much more fat to lose? If you do, then perhaps you need to eat less fat for a while, because if your body is getting enough in then why bother with taking from storage. Or perhaps you need to reduce protein intake? Longer periods of fasting? Experiment.
  14. Susan Puckett
    Makes sense!
  15. Joshua
    Wow this article and comments can't be serious. Not once in this ridiculous article did I read about working out. Changing your diet alone is not enough to start losing weight. It plays a major role, but you also have to work out and be active. Being in a calorie deficit with exercise is what causes weight loss.

    Every human body is the same. People make all kinds of excuses when really if you eat healthy, stop eating giant portions and work out hard enough, you will lose weight. Simple. Stop with the mental gymnastics to explain why people are overweight and not losing.

    Reply: #16
  16. Kristin Parker Team Diet Doctor

    Wow this article and comments can't be serious. Not once in this ridiculous article did I read about working out. Changing your diet alone is not enough to start losing weight. It plays a major role, but you also have to work out and be active. Being in a calorie deficit with exercise is what causes weight loss.
    Every human body is the same. People make all kinds of excuses when really if you eat healthy, stop eating giant portions and work out hard enough, you will lose weight. Simple. Stop with the mental gymnastics to explain why people are overweight and not losing.

    We address exercise specifically here -

  17. KERRY
    You make some interesting claims. I don't see any clinical studies listed. I don't see double-blind study with large groups. Maybe you just sell books?
    Reply: #18
  18. Gentiann
    Why don't you check his website, as he suggests it, for references to studies?
  19. D
    This is Asanine. Another person trying to sell you. I can show you countless scientific studies proving you 100% wrong. Calories in vs out is THE primary cause of fat loss. Are there other factors? Absolutely. But at the end of the day, calories are what matters.
  20. Wade Wilson
    Then explain if your idea of “high insulin” is the primary driver of fat gain, why is it not included in this article that protein raises insulin and a high fat + high protein meal raises insulin levels higher than a high carbohydrate one?

    Probably because muscle needs insulin

    Or how diabetics and other low carb dieters can gain build muscle (in turn results in fat gain anyways since one can’t be gained without the other to some degree) which for muscle to be built, ONLY will be built due to a surplus of calories. There’s a difference between the DIETARY view of “CICO” vs the BIOLOGY of CICO.

    Biology dictates everything related to how calories work within the body in various involuntary ways, CICO still happens due to various metabolic processes in the body and after all this is literally how the metabolism works, by using a set amount of calories daily to keep you alive and functional, such as BMR.

    The dieting view of “if I reduce my calories by 3500 I’ll lose 1lb of fat” isnt an absolute since some people may have to reduce their calories by MORE than 3500 to lose 1lb of fat (and btw 3500 is roughly 1lbs of Fat) and for others it may even be LESS before muscle is lost, this isn’t because CICO as biology doesn’t “work” this is because all bodies are different, CICO still and ALWAYS applies due to biology, and the “CICO dieting view” or As you call it “calorie reduction as primary” STILL doesn’t mean CICO DOESNT work, it means the majority of people (and there are studies of such) DONT adequately know HOW to count calories properly and make tons of errors all the time. for those who DO use the calorie reduction/counting/CICO “diet”, still lose fat and build muscle just fine.

    Because Reducing calories regardless of counting them directly (which would be the cico “diet” or cal counting/cal reduction as primary method) or indirectly reducing through diet when calories aren’t counted for, (example the keto diet, less carbs =less cals consumed + high protein = more satiety & more cals burned through TEF + high fat = more satiation to not eat as much food= calorie reduction = a deficit of calories = CICO APPLIES STILL)

    But that’s usually left out of these sorts of websites and books and articles. The SOLE reason we even lose body fat to begin with is due to the starvation response by the body. Which is ONLY dictated by QUANTITY of food (aka calorie amount) and not TYPE of food. “Bad” hormones or BSW or not, reducing calories is the only thing that’ll cause fat loss and muscle loss. And vice versa as a surplus. (And yes hormones & possible medical conditions can affect to some degree HOW the body utilizes the macros & calories but it’s definitely not THE reason why people are gaining weight (fat/muscle) it’s STILL caloric intake as a whole)

    But if something other than calories are the “reason” that causes obesity, If it WAS, then you’d see tons of people building muscle in a surplus of calories WHILE lose fat by eating X way/foods. Yet this is an impossibility.
    (And for those who actually do build muscle while losing fat is usually due to having a significant amount OF fat which already IS a stored surplus of calories as energy In the body, then uses towards the new muscle being built, since excess fat is due to a surplus of calories)

    After all this (below) wouldn’t be possible if it was otherwise something else besides calories.

    Examples here:
    Mark Haub eating “junk food diet” while losing 27lbs of fat AND improving overall health (health improves with fat loss regardless of how it’s done)

    A woman who (note the websites title) gained 20lbs eating a low carb diet, she said she estimated eating 4000 calories a day (huge amount by anyone’s standards) yet, regardless of the idea of keeping “insulin levels low” is viewed, still doesn’t matter when in a surplus of calories.

    Building muscle on A keto diet
    Again only possible with a surplus of calories

    Diabetes type 1 building muscle
    Still needs a surplus of cals

    Go ahead and try refuting calories having nothing to do with weight loss or gain, yet nearly a century worth of countless irrefutable facts, evidence, studies, real world examples etc. show that regardless of how much you try to show otherwise, you’ll always be wrong, that’s how facts work, you’re fighting a losing battle. And if that’s not enough, your own biology is proof of that already.

  21. sajet
    Your solution at the end essentially seemed to boil down to "cut calories" but just target it a bit.

    Of course bodies will vary too much to say "cut by this amount, you'll lose this much", but at the end of the day you're still going to be losing if you can find the right amount to cut. And it's a good idea not to use your calories on junk, because it's easy to overdo and less filling. This doesn't require some overly complicated temperature regulation system to be considered. And finding real meals to achieve this is much more sustainable than having one Big Mac a day.

    I can't tell if the people here cutting carbs but keeping high fat for years with no results are serious. Actually break down your caloric intake. High fat screams high calories, and easy to overdo, so you're clearly not cutting enough consistently. Also why would you continue to do the same thing if it's not working??

  22. 2 comments removed
  23. C Freeman
    Doing the same thing over and over and expecting different results is the definition of insanity.
  24. 2 comments removed
  25. B Long
    Yeah I know this was from 2018 but as the others above have said to anyone who has read this article and believed it's BS don't listen. Calorie in vs Calorie out is truly the only factor that matters when losing weight. If at a specific amount of calories per day your body weighs X amount if you cut any noticeable amount of calories (100-300+) and maintain that everyday your body will lose weight until it finds a new weight at the amount of calories your eating it really is that simple. Exercise plays a major role in weight loss because many people find that they begin to not only be more health conscious day to day. Exercising also boost endorphins which are natural pain killers among other hormones that boost your mood. This can help lower stress and anxiety which people often cope with by binge eating. Exercising outside of your home also physically removes you from a place where food is easy access. Finally exercising burns more calories than resting further increasing your caloric deficit and therefore weight loss. Finally while you do not have to buy organic GMO free BS buying fresh produce/meat and cooking your own meals at home allows tighter control over ingredient and therefore portion sizes where as going out your likely to overeat every time especially at a cheap fast food joint. Finally this number jumps around a lot but a general rule of thumb is that to burn 1 pound of body fat anywhere on your body you need a ~3000 calorie deficit. Therefore if you cut 100 calories a day out of your diet you may notice yourself lose about a pound a month until your body finds equilibrium which is different for everyone but it is primarily based on Age, Sex, Metabolism, and genetics. Scale as needed. Hope this helps.

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