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If you are attempting to lose weight via dieting and/or exercise, you will see this number EVERYWHERE on the internet.

If you create a deficit of 3500 calories you will lose one pound, as simple as that.

But is that really true?

Surely there are many factors which will affect how true this is?. That different energy sources have different energy densities, such as muscle and fat, for one.

And where does this number even come from, how is it derived?

  • It may be true that 1 pound of fat, when metabolized, provides 3500 Calories of energy. However, this does not mean that removing 3500 Calories from your diet or spending 3500 Calories on physical activity will necessarily lead to having 1 less pound of fat in your body. Many factors affect which energy sources your body will use, and the body also adapts to energy expenditure in different ways. – octern May 4 '15 at 5:37
  • Keep in mind these are "food" calories; 1 calorie is enough to heat 1 Kg of water 1 degree C. Not to be mixed with" science" calories , 1 calorie is enough to heat 1 g of water 1 degree C. A 1000 : 1 ratio, – blacksmith37 Nov 20 '17 at 20:28
  • @blacksmith37 a 'food calorie' AKA Calorie, is just an easy way of saying kilocalorie, ie one thousand calories. While it is incorrect to say calorie when it's actually a kilocalorie, it's widely common. I guess I shouldn't be speading it though.. – Aequitas Nov 20 '17 at 23:28
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The original 3500 calorie theory comes from a correspondence published in 1959, by a Dr. Max Wishnofsky, where he equates it to pounds lost in observed obese patients.

It's further perpetuated by badly applied mathematics. White adipose tissue has the responsibility for energy storage in the body. This tissue is composed of anywhere from 60% to 85% lipid (fat). If you take the commonly accepted 9 calories of energy per gram of fat (Which is also not quite accurate), you get the following formula:

9 (calories/gram) * 454 grams (grams in a pound) * .85 = 3465 calories.

So, the original estimation was that there were 3500 calories in a pound of human fat, so to lose a pound you had to burn 3500 calories. Since this "makes sense", it was widely repeated and used, and became entrenched. It is not accurate, and implying that to lose a pound of fat you have to burn exactly 3500 calories is erroneous.

Edit: While researching something else, I came across this article, titled "Farewell to the 3500 calorie Rule", on Today's Dietitian website. One paragraph from the article:

It's been estimated that the 3,500-calorie rule is cited in more than 35,000 educational weight-loss sites.1 In September, the Journal of the American Medical Association published a patient handout titled Healthy Weight Loss, in which the first sentence states, "A total of 3,500 calories equals 1 pound of body fat. This means if you decrease (or increase) your intake by 500 calories daily, you will lose (or gain) 1 pound per week."2 Undoubtedly, the 3,500-calorie dogma still is being taught even though it's been shown that it simply doesn't work this way. So where did the 3,500-calorie weight-loss wisdom come from? It originated from researcher Max Wishnofsky, MD, in 1958, who calculated that 1 lb of fat stores approximately 3,500 kcal of energy.3 It was appealingly simple, and it stuck.

  • so 3500 calories only equals a pound of fat (on average) if you lose muscle mass for instance, I'm assuming that muscle would have less calories, you would end up losing a lot more weight with the same calorie deficit than if you were losing fat? – Aequitas May 1 '15 at 3:01
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    Also are you saying that it is true and correct? your tone indicates that you think that this isn't the case. – Aequitas May 1 '15 at 3:02
  • We can discuss this in chat, comments are for improving questions/answers, not extended discussions. :) – JohnP May 1 '15 at 4:00
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    Asking if you believe the conclusion to be true/correct seems a good improvement of the answer. – Paul May 1 '15 at 7:43
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    @Asmani - There is no way to tell, especially as the 3500 calories is not correct to begin with. Also, when you lose weight, it will not be exclusively muscle or fat, it will be a combination. Also, it will vary from person to person. – JohnP Nov 20 '17 at 20:39
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It is, at least, overly simplified.

The average amount of water in adipose tissue is 13%. In addition to that, it also contains approx. 3% protein. The remainder is fat.

Lard, which should have a similar calorific value as human fat, provides ~8980 calories per kg.

To simplify this calculation we assume that 1 kg of protein provides 4000 calories and 1 kg of fat 9000 calories (in other words ratios of 1:4 and 1:9).

The average kilo of adipose tissue (fat tissue) contains 840g fat and 30g protein. Which amounts to a calorific value of 7680 calories per kilo.

Translated into pounds that is 3484 calories per pound, which is pretty close to the number in question.

The problem is that this is based on average values that have wide ranges attached to them.

The water content of fat tissue can vary between ~4 and ~40% and the protein content between ~2 and ~3.5%.

This means the calorific value can vary between 5540 and 8540 calories per kilo (or 2510 and 3870 per pound) of fat tissue.

Sadly, it also seems that the water content is lower for those above standard weight. So whoever needs to lose a couple of pounds because of health reasons should rather apply 3900 per pound.

The numbers are based on this study. It is a bit old but as the numbers are based on actual tissue samples, I doubt they are too far away from the truth. What might have changed is the average. At least in some countries, as obesity rates are much higher than 50 years ago.

Regarding the water content of body fat, try a watermelon test. Replace an intake of 1000 calories with watermelon worth 500 calories. Drink as much water as you usually do. The extra water intake will most likely lead to an increase body weight on the next day, even though your calorific intake was lower.

The above-mentioned study refers to: "THE CHEMICAL COMPOSITION OF ADIPOSE TISSUE OF MAN AND MICE." LORETTE W. THOMAS, Department of Physiology, Edinburgh University. (1962)

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    Welcome to Health.SE, life-on-mars. Since health is an important topic, the site has a strict policy that all answers should be backed up with reliable references so that the answer can be independently verified, regardless of the reader's background. See this list of reliable sources. You did that, +1, but a bit of quoting from your lonk would further improve it.Feel free to visit the help center or Medical Sciences Meta. – LаngLаngС Jul 14 '18 at 18:24
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    cont. Your link might or might not answer the question. However it would be preferable to include the essential parts of the answer here, and provide the link for reference. If you edit your answer to improve its quality, take a look at Common format for references. – LаngLаngС Jul 14 '18 at 18:27
  • @LangLangC As I said, the numbers I provided are "based" on the study. It is a paper about the composition of adipose tissue and not a newspaper article on how much calories you need to burn to lose 1 pound of fat. In order to answer the question, I had to do calculations on these numbers. No serious scientific study would directly answer a question like the one that was asked here. I don't see how I could quote from such a paper without deviating from the topic. As for the "format for references", the link leads to a discussion. It's not obvious what this "format" is supposed to be. – life-on-mars Jul 14 '18 at 19:04
  • Part of what I wrote is to introduce you to some standards and customs, although you didn't violate them here. Almost a standard welcome. – The link title and format are a little non-descript, (some form of author/title/year would be good to have here) directly to a PDF (bit old in content, I have to say, indeed ;) and might be subject to link rot. I already upvoted and these are just minor suggestions. No need to worry on that. (Btw&completely offtopic: Bowie or Sam Tyler?) – LаngLаngС Jul 14 '18 at 19:13
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    @LangLangC I've added title/author in a footnote. That was the only definitely useful info I was able to extrapolate from that discussion. Link rot makes sense. I see that on Wikipedia everyday. An older study actually makes sense as a reference, as the question apparently also includes historical context and the study refers to a number of earlier studies from the 1950's. (off-topic topic---a decade before Bowie: Valentine Michael Smith.) – life-on-mars Jul 14 '18 at 19:25

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