CaloriesMen's HealthPublic HealthWomen's Health

Where does the 3500 calorie theory come from?

The simple answer is “I don’t know” and nor do any of the public health bodies/obesity organisations that use it, as this post comprehensively confirms. The “Prove it or stop using it” post invites anyone to source/prove the calorie formula. The challenge was first thrown out in my 2010 obesity book and still goes unanswered.

This post is to share the earliest reference that I have found to the formula (although it doesn’t actually state it). I’d be very interested in anything earlier that anyone can find and even more interested in proof. There is enough counter evidence already that I can guarantee that proof cannot and will not be found.

Lulu Hunt Peters (1918)

In a book called Diet and Health by Lulu Hunt Peters (1918),[i] Hunt Peters states “Five hundred Calories equal approximately 2 ounces of fat. Two ounces per day would be about 4 pounds per month, or 48 pounds per year. Cutting out 1000 Calories per day would equal a reduction of approximately 8 pounds per month, or 96 pounds per year.”

An article from the Chicago Daily Tribune (Sept 15, 1959) asserts “a pound of fat is lost whenever the body burns up 3,500 calories by diet or exercise”.[ii] The way that this is asserted, suggests that it is already a well known ‘fact’ by this date, but did Hunt Peters start it or perpetuate it?

A couple of extracts in Diet and Health make me think that it is plausible that Hunt Peters did effectively originate “The Calorie Formula”:

1)  On the opening page, Hunt Peters says: “I am sorry I cannot devise a key by which to read this book, as well as a Key to the Calories, for sometimes you are to read the title headings and side explanations before the text. Other times you are supposed to read the text and then the headings. It really does not matter much as long as you read them both. Be sure to do that. They are clever. I wrote them myself.” (Hunt Peters own emphasis in italics).

2)  Chapter 2 “Key to the calories” has the following: [Sidenote: Pronounced Kal’-o-ri]. So calories were so little known at the time, that Hunt Peters needed to tell people how to pronounce them. If only we had stayed so blissfully ignorant about calories, or at least had come to see them as fuel for the body – which is all that they are.

If Hunt Peters had the right to be proud of her ‘cleverness’ and if she really did break something revolutionary to the women of Los Angeles in 1918, we may indeed have one woman to ‘thank’ for “The Calorie Formula”, which is the foundation of weight loss advice to date. If anyone else knows of a reference earlier than 1918, I would be most interested for research sake, but it actually matters less from where this originated and more that it has held as ‘fact’ for almost a century and yet it cannot be proven to hold true.

p.s. I know the background to the estimated calories per gram (which are wrong) and how the 1lb is assumed to be 3500 (which is also wrong). I’m looking for the first reference to the calorie formula/theory (the two parts being: 1lb = 3500 cals; to lose 1lb you need to create a deficit of 3500 cals) or an earlier application of the theory – without actually stating it – than Lulu Hunt Peters. It’s a very specific statement, which has pervaded virtually all dieting literature and which millions, if not tens/hundreds of millions of people are following right now. And we know not from whence it came!

[i] Lulu Hunt Peters, Diet and Health (with key to the calories), published by Chicago The Reilly and Lee Company, (1918).

[ii] T R Van Dellen, “How to keep well”, Chicago Daily Tribune, (15 September 1959).

33 thoughts on “Where does the 3500 calorie theory come from?

  • Pingback: How to Lose a Stone - Colin M Stone

  • In most weight change calculations fat and fat change is measured in terms of the actual grams of fat being lost, not in grams of fat tissue (very different things, indeed). The rest is measured as fat-free mass change (FFM). Thus the 3500 kCal per pound of fat really makes zero sense in using it for weight-loss calculations, even setting aside the obvious issues presented by people actually using different proportions of fat and fat-free mass depending on their initial weight, BMI and BFP. Some further thoughts on this which might be of interest, as well as mentions of some high-profile institutions which are still propagating the 3500 Calorie myth: .

  • Hi Zoe

    thanks for the great information. I was just wondering which types of fats should bodybuilders consume? This is a question I get asked often from my readers at I just wanted to get your opinion on it.

    • Hi Marcus – any real fats found in real food – those in: meat; fish; eggs; dairy (if tolerant to it); nuts; seeds (watch nuts & seeds if watching weight); avocados; olives etc and natural oils/fats for normal cooking e.g. butter/lard/coconut oil/olive oil.
      I’m not a fan of highly unsaturated oils (sunflower/rapeseed/soybean etc) – especially important to avoid in cooking. I’m also not a fan of eating fat for its own sake (e.g. butter coffee) – unless you’re doing genuine LCHF which means your carb intake should be c. 25g a day and protein also moderated. Not many people do LCHF properly!
      Hope this helps
      Best wishes – Zoe

  • Love this information! I’m wondering if you have come across a subset of people who this doesn’t hold true for. I’ve been struggling with weight for years. I did the HCG diet with success years ago but it was short term. I have been eating strictly ketogenic (little to no dairy) for a couple of years. I also utilize IF weekly. I am very strict and disciplined. I also exercise regularly. Yet I somehow manage to gain 3-5 kg a month. It is purely fat. I have seen countless doctors and am being treated for hypothyroid and hormone balance but it’s not extreme. It doesn’t seem the likely culprit. Carbs of ANY form cause instant and extreme weight gain. But I have been low carb for years and completely sugar (in all forms) free for even more years. I eat grass fed and organic as well. Have you come across others like this? Suggestions?

    • Hi Heather
      Many thanks for your kind words – not sure what specifically “this doesn’t hold true for” is referring to? The calorie theory doesn’t hold for anyone!

      I hadn’t heard of the HCG diet – just looked it up and if it’s the VLCD with hormone injections that I’ve just been horrified by on the net, you may well have screwed up your body and it may take time to recover from this. People who lose weight on low cal/let alone very low cal, invariably regain and more – you could still be fighting that regain phase.

      Are there people for whom ketogenic diets don’t work? Yes – but rarely. Women especially seem to lose out in the weight loss gain – not surprisingly because weight is about hormones, not calories, and females have far more hormone stuff going on than males. I can’t suggest much without knowing more – we have an 10,000 word article in our club members’ area ( about 10 things to work through if you’ve not lost for some time. Covers meds, medical conditions, previous dieting history and more. I would suspect something else going on – maybe PCOS, maybe insulin resistance – you’ve already mentioned a couple that won’t help – it doesn’t appear to be diet :-(

      Best wishes – Zoe

  • Hi Zoe, :)

    The caloric hypothesis is totally incorrect from the starting gate- by principle.It totally contradicts the conservation of matter principle. There is NO caloric energy being converted into matter in a human being. Further, humans are chemically powered. We are not nuclear powered as the caloric model suggests. Humans CANNOT convert fat tissue ( which is matter- kilograms etc. ) into energy or heat ( kilojoules).

    The caloric hypothesis people are scientifically illiterate idiots ignorant of stoichiometery . This applies even to most medical doctors.

    • Hi Razwell – I liked your comment :-)
      Best wishes – Zoe

  • I can confirm that the calorie theory is still alive and well. Having been referred by my GP to the Camden Weight Management Service, I went along last week and the dietitician clacked it out. She wasn’t very happy when I kept asking for proof of her assertions. Oh she also said you can’t reverse or prevent diabetes. Her lecture was about sugar. This week her lecture will be about fats. Oh yes one other thing which made me laugh out loud was that saturated fat causes heart disease. Don’t eat saturated fat. Then a bit later, eat eggs because eggs are good for you. No limit on the amount of eggs you can eat. “Oh but they contain saturated fat and we aren’t supposed to eat that so do we just eat around the saturated fat molecules” asked I. Can’t wait for this week.

    • Hi Elle
      Many thanks for that – made me chuckle at the end of a humourless day! ;-)
      Best wishes – Zoe

    • Hi, I attended a diabetes class as a friend of a diabetic, and because I am interested in proper health.
      The information presented is quite scary and oft wrong. re cholesterol and fat in particular.
      I am hoping my friend can improve his diabetes and his aim is to get off meds. Unfortunately his indicators are quite high at the minute. I will steer him towards a higher healthier fat diet amongst other things (hydrate, exercise, more raw, less processed). They mean well, but WHO ARE THEY LISTENING TO.
      Week 1 done, and 5 to go. Great article Zoe, keep up the good work.

  • All I know is no one has ever been ever to prove you cant eat more calories then your body needs and NOT gain weight. Most every expert agrees it takes 3500 cals to make a lb so why not – 3500 to lose a lb. this is why the low carb thing is nonsense, low carbs = eat less , there is no magic..

    • 1) In “Evidence Based Medicine” the agreement of experts is rated as the lowest form of reliable evidence.

      2) The expert opinion on the cause of stomach ulcers was that “Bacteria cannot be the cause, because the acid content of the stomach is so high that bacteria would die.” A fairly recent Nobel prize in medicine was awarded to the Australians who showed that most cases of ulcers could be cured by the administrations of antibiotics, which kill a specific stomach bacteria.

      3) I don’t know what you mean by “Most every expert agrees it takes 3500 cals to make a lb.” There is a difference between a pound of fat containing 3500 Calories of energy as measured in a laboratory bomb calorimeter and the claim that X excess calories will convert in the body into 1 pound of fat. One is a statement of energy content revealed by combustion and the second is a statement of energy conversion from one chemical form to another. Can you elaborate on the meaning of your statement?

  • Ash seems to have the answer. First use must be later than William Banting’s “Letter on Corpulence” 1863. This is available online. He cuts carbs to lose weight. I expect you have read it. The craze for dieting started with him and was known as “banting”.

    • Hi Jenny – Banting wasn’t about calorie counting – quite the contrary – as you note it was about carb cutting. LCHF diets use the term Banting today.

      I’m still looking for the first reference to the calorie formula/theory (1lb = 3500 cals; to lose 1lb you need to create a deficit of 3500 cals) or an earlier application of the theory without actually stating it – than Lulu Hunt Peters. It’s a very specific statement, which has pervaded virtually all dieting literature and which millions, if not tens/hundreds of millions of people are following right now. And we know not from whence it came!

      Best wishes – Zoe

  • One thing I love about this blog is I often end up having to figure out how to state my position to see how it compares with the topic at hand. :-)

    I don’t mind thinking of the 3500 cal concept as a rough rule of thumb (i.e. “3500 cal is roundabout the amount of usable energy stored in one pound of adipose tissue”) but the idea of it as some sort of functional law is just mind-boggling.

    My question is this: were the researchers who came up with it looking for a metabolic law in the vein of F=ma, or were they just looking for some empiricism to help explain observations. Empirical rules of thumb have tremendous value when used properly (the qualifier here is absolutely crucial).

    But if people are misinterpreting an empiricism as a functional law, that’s not so much a fault of the rule of thumb as it is the people who are abusing it. I don’t think you’ll ever find a source that calls 3500 cal/lb a law because I don’t think it exists. I *do* think you’ll find many, many people who hastily grab the number and run with it in directions is was never intended to go. Which, I suppose, is your point.

    (And thanks to the previous commenters: lots of good literature to read now.) :-)

    • Hi David
      I see it used daily as a law – if you eat 100 more calories a day you will gain 10lb a year – oh no you won’t! And the people who use it a) have no idea where it comes from b) can’t prove it and c) won’t stop using it.
      If it were a rule of thumb (see this post it’s out by multiples, not margins – so it’s a useless rule of thumb. Oh and millions of people are using this ‘rule’ on a daily basis having been lied to.
      This needs to change.
      Best wishes – Zoe

      • Totally agreed. 100 cal/day is easily within the body’s amazing ability to adapt to changing food availability.

  • The thing that gets me about any discussion about calories is the elephant in the room that no one ever mentions. Food (any food) is POTENTIAL energy only. Just because we have eaten it does not mean we are going to use it or store it.

    Has anyone ever calculated the calories we “poop” “pee” and sweat (body oils) and subtracted it from inputs

    • Hi Brian – even bigger elephant in the room – thermodynamics says naff all about weight – only energy. We are the ones who have assumed weight to energy conversions (in and out) and we’re wrong! Hence why I won’t stop attacking the calorie theory until it is publicly consigned to the scrap heap and millions upon millions of people are liberated from complete nonsense!
      Best wishes – Zoe
      p.s. yes – the weight of bodily losses has been calculated in calorie chambers – still completely misses the weight/energy points (and is pretty unpleasant!)

  • I believe this is all based on the notion that a gram of fat contains roughly 9 calories. Hunt Peters says that “500 calories equal approximately 2 ounces of fat.” This is true if you combust 2 ounces of fat in a bomb calorimeter and measure the heat produced. 2 ounces is about 57 grams. 57g x 9 calories/g = 513 calories.

    1 pound of fat (455g) thus would yield about 4095 calories in the bomb calorimeter. The 3500 calorie figure subtracts a fudge factor to account for the fact that 1 lb of lost body weight includes some water and lean tissue and thus contains fewer total calories than a pound of pure fat.

  • Here’s where it’s (possibly) first used in human nutrition, neat page where you can read the book old school style, can’t find the specific reference yet, will leave that task up to other readers:


    “A manual of human physiology” ~ Joseph Raymond, 1894

    • Hi Ash
      Many thanks for this – I’ve downloaded it and searched for “calorie” and this is the only passage that contains “calorie”:

      “Heat-iinit. — The standard of measure of heat is the heat-unit or calorie. It is the amount necessary to raise
      the temperature of i gramme of water i° C. A kilo-calorie is equal to 1000 calories, and it represents the
      amount of heat necessary to raise the temperature of i kilogramme (litre) i°C. It is estimated that an average
      man produces daily 2500 kilo-calories, which is about 100 kilo-calories per hour. During active exercise this
      amount is greatly increased, even to the amount of 300 kilo-calories hourly, while during sleep it is only 40 kilo-

      There are some funny character changes, as I went for the text option to keep file size manageable. Nothing about the calorie theory (3500 as applied to weight loss) here :-(

      Best wishes – Zoe

      • I think part of the problem is you might be chasing the wrong definition, these folk were using the metric system and so they spoke in joules, not calories.

        As I mentioned in the other post, it all really begins with Atwater in the late 1800.

        Here’s a calorie timeline:


        Then it was cemented in place in 1918 with Lulu Peters book “Diet and Health With Key to the Calories”:


        • Hi Ash – many thanks for this – the cal timeline is great. If, in the ones pre-1918, no one states the cal theory before Lulu, she may have it! Albeit inferred, not set out in the way we do today.
          Isn’t is interesting though how things become folklore and no one has a clue where they first came from! I still want that first statement with the 3500. Some people claim it was Wishnofsky (mentioned here, but that was 40 years after Lulu and Wishnofsky used 3750 as if it were gospel!
          Bye for now – Zoe

          • Hi Zoe, glad you liked my calorie counting timeline. And thanks Ash for linking to it. I didn’t think anyone would ever care about it besides me.

            I’ve been researching the concept of calorie counting for the past 6 years for a book I plan to write debunking calorie counting in all aspects.

            Zoe, if you read Wishnofsky’s article to the end, he does start out by stating 3750 but later on discusses 3500 as if 3500 is actually correct, but also that it may not apply in all situations. I think overall he mentions 3500 enough in the full article that it is the original source of the 3500 rule.

            I think Lulu was the first to try to quantify the relationship between calories and weight, but Wishnofsky was the first one to put 3500 on the map.

            However, the concept of calorie counting, and specifically, the idea of measuring food in calories pre-dates Lulu. That’s why I wrote the “Origins of Calorie Counting” blog post:


            To me, the problems with calorie counting go way beyond the 3500 rule. The bigger problem is the thinking that we can predict weight changes based on calorie amounts.

            The idea that weight is a mathematical function of energy, with a one-to-one mapping, and a predictable weight result, based on energy balance, is simply wrong. It confuses mass and energy.

            When you put a bag of groceries in your car, your car weighs more, right? But why? Is it the calories in the food that causes your car to weigh more, or is it simply the weight of the food? Only in nutrition science do we somehow think that energy causes weight changes, when in all other domains, we know obviously that any object gains weight by gaining mass.

            Besides, calories are invisible and intangible, so how can they affect your weight?


          • Hi Kenny
            Great to ‘meet’ the originator! I could not agree more with all you say – I use the example of a power station. We put hundreds of thousands of tonnes of coal into a power station and get weightless electricity. Allowing for the second (universally ignored in the weight loss misapplication) law of thermodynamics – energy will have been lost and energy will have been used up in making available energy and then the first law of conservation, allowing for the non closed system, applies. Energy may well be conserved – but weight!?
            Love your last sentence – we need as many ways of getting this across as possible – it’s still absurdly widely believed!
            Best wishes – Zoe

  • The calorie theory/religion was fabricated around 1850, and 50 years later progressed to being misapplied to human biology after Atwater’s demonstrations:

    “The calorie was not a unit of heat in the original metric system. Some histories state that a defined Calorie (modern kcal) originated with Favre and Silbermann in 1852 or Mayer in 1848. However, Nicholas Clément introduced Calories in lectures on heat engines that were given in Paris between 1819 and 1824.

    The Calorie was already defined in Bescherelle’s 1845 Dictionnaire National. In 1863, the word entered the English language through translation of Ganot’s popular French physics text, which defined a Calorie as the heat needed to raise the temperature of 1 kg of water from 0 to 1°C. Berthelot distinguished between g- and kg-calories by 1879, and Raymond used the kcal in a discussion of human energy needs in an 1894 medical physiology text.

    The capitalized Calorie as used to indicate 1 kcal on U.S. food labels derives from Atwater’s 1887 article on food energy in Century magazine and Farmers’ Bulletin 23 in 1894. Formal recognition began in 1896 when the g-calorie was defined as a secondary unit of energy in the cm-g-s measurement system. The thermal calorie was not fully defined until the 20th century, by which time the nutritional Calorie was embedded in U.S. popular culture and nutritional policy.”


    “History of the Calorie in Nutrition” ~ James L. Hargrove, 2006

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.