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Obesity Myth #1: The 3,500 Calorie Rule

Yesterday, the New England Journal of Medicine published a paper that addresses common myths, presumptions, and facts about obesity.

As the authors note in their introduction,

“Passionate interests, the human tendency to seek explanations for observed phenomena, and everyday experience appear to contribute to strong convictions about obesity, despite the absence of supporting data. When the public, mass media, government agencies, and even academic scientists espouse unsupported beliefs, the result may be ineffective policy, unhelpful or unsafe clinical and public health recommendations, and an unproductive allocation of resources.”

In this paper, the authors address seven myths, six presumptions and nine facts, which I hope to address individually in upcoming posts.

The first myth addressed in the paper is the common misconception that a continuous daily excess of a few calories per day will result in continuous weight gain.

This myth (also referred to as the 3,500 Calorie Rule) is often presented in a way that numerically adds up the number of excess calories you may be eating per day (say 100) and translates this into weight gain by simply equating 3,500 extra calories to one pound weight gain.

Thus, even academic publications often suggest that a 100 extra calories per day over a year (say about 350 days) would result in 35,000 extra calories or a ten pound weight gain.

You will also often find the converse, where simply burning an extra 100 calories a day is equated to losing 10 lbs.

This, as explained in the paper is a myth because such simplistic calculations do not take into account the physiological mechanisms that result in compensatory energy conservation or expenditure, thereby limiting changes in body weight.

Thus, although a pound of body fat may well represent about 3,500 calories (which it roughly does), an extra pound of body fat is not simply the numerical result of ingesting an extra 100 calories per day for 35 days.

Nor does a daily caloric deficit of 500 calories result in a weight loss of one pound a week, week after week after week, till you finally disappear.

As I have previously explained, significant and ongoing weight gain or weight loss actually requires a substantially greater level of daily caloric excess or restriction that may have to incrementally increase over time to sustain continued gain or loss.

It is therefore safe to ignore statements that are commonly found both in academic publications and in popular media presenting simplistic statements like, “an extra potato chip a day over 20 years can lead to a 50 lb weight gain or an extra can of pop a day can lead to a 20 lb weight gain in one year”.

In reality, ingesting 3,500 extra calories does not simply translate into an extra pound of body fat – nor does burning 3.500 extra calories result in a pound of weight loss.

Or, as I say in my talks, “This is not physics, this is physiology!”

For a detailed discussion of how many calories it actually takes to lose or gain weight click here.

Edmonton, AB


  1. I am always amazed that people think that metabolizing 3,500 calories is the same for everyone, and totally the result of their behavior.

    I might be comparing notes on my Buick with another Buick owner of the same model and year. If I share that my gas milage is 3 miles per gallon better than hers, she doesn’t immediately jump to the conclusion that my driving habits are superior to hers. She would explore that possibility, but also look at a broad range of other potential causes — clogged mechanisms, potentially worn-out parts, etc. And, the thing is, a Buick is a limited machine by comparison to the human body. How efficiently or inefficiently the human body processes its fuel depends on mechanics PLUS dozens, hundreds, maybe thousands of additional genetic, environmental and hormonal variables! And yet, two women, same age, different weight will leap to the assumption that the fat one is lazy and gluttonous. If she would simply cut 500 calories a day from her diet or burn an extra 500 with exercise, she’d soon be trim for life. Lah-de-dah.

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    • Why is it that most obese people live in the USA? And some of the healthiest in Sweden, for example? It isn’t genetics or environmental factors. It is good or bad habits.

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      • That’s factually false. The most obese country on Earth is Nauru, where about 95% of the population is obese.

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        • Are you claiming that there are more obese people in Nauru (population 13,000) than in the USA?

          How could Nauru have anything to do with whether or not “most obese people live in the USA”? It couldn’t. It’s just too small to matter.

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  2. Incidentally, as an addendum to this myth, it also implies that the commonly heard advice that, “Small changes, over time, can lead to big changes in body weight”, are essentially nonsense. Losing (or gaining) a large amount of weight requires substantial, persistent and often incremental changes in caloric intake or expenditure to sustain. Thus, for e.g. even completely giving up the one teaspoon of sugar in my daily cup of tea, although adding up to 1000s of fewer calories over the years, may do almost nothing in terms of reducing my body weight. But, if I drink 10 cups of tea each day, and cut out sugar in all of them, thereby saving hundreds of calories per day, I will definitely expect to see some weight loss. I guess what you consider a “small” change is a matter of perspective.

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    • Every little helps.
      It’s not rocket science.

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  3. The study of obesity is, for the first time, exploding with new information and new treatments. “Myths, Presumptions, and Facts About Obesity” is another game changer. I’m sharing your post with me readers and patients as headline news.

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  4. bravo, and well-expressed, Dr. S!

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  5. Yes, many of the authors of the paper have ties to food, pharmaceutical and commercial weight loss companies – this neither validates nor discounts the paper for what it is. I tend to worry more about people who have no conflicts to declare – it is usually these “holier-than-thou” ideologists that I tend to mistrust – it is the ‘hidden agendas’ of these folks that I worry about. Let him, who truly has no ‘conflict’ cast the first stone.

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  6. I don’t buy the first myth. I do believe that we don’t eat an exact amount overage, but if one does develop a new habit (say, getting a cola for the ride home from the brand new vending machine outside work or school), there is a good chance the body won’t change physiologically, nor that the person will have enough energy suddenly to burn those extra 100 to 180 calories.

    We see so many people at average weights becoming obese by their thirties that aren’t suddenly overeating one day to become obese, and the weight gain seems gradual. To suggest that the minimal over-consumption of calories is only a myth is to wreck the potential for stopping potential roads to obesity and metabolic syndrome before people get there.

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  7. Great post Arya!

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  8. It is very naive to dismiss the conflict of interest of authors of a study, especially with such strong ties as being board members of drug , food companies and food lobby organizations. There are many people in the nutrition and health field with no business/industry affiliation and to worry more about these, as you put it ‘holier than thou ideologists’ is to ignore the reality of bias in studies by people who represent industries that would profit from their findings.

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  9. Yes, the calorie system is not accurate in many ways, as explained in this post. Still, since I’ve been watching calories, the weight is going down faster than ever. It still is a good tool to use, at least for me.

    🙂 Marion

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  10. I learned the hard way, a long time ago, that you can throw all the best metabolic research at the public, but if it doesn’t fit their internalized moral paradigms, it’s completely useless. Thank you for this post and for stressing these issues. If enough experts bring up and stress these issues on a regular basis, they will seep very slowly into the public consciousness, and will take root within a few generations.

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  11. I definitely think articles like this are important. There’s too much oversimplification of how to lose weight that it becomes maddening. For instance, a couple years back I replaced black coffee with a cola in the morning and actually lost weight ( this was after I had given up on the low carb method). Obviously, this is disgusting, because cola is a horrific thing to put in your body, but I think I just ended up consuming less throughout the day, and felt more need to compensate and run harder later in the day that it wasn’t sooo detrimental to actually make me gain 10 lbs within a year.

    Now I’m plus 30 and it seems like weight loss is impossible, so when I look for information online I am driven crazy by the 3500 calories is a pound thing. With my running 10 kilometers, 6 days a week, I should be easily losing 1-2 lbs weekly. I don’t lose anywhere near this much and I am 30 pounds overweight. I think everyone is an individual and needs to see a dietician and actually get their basal metabolic rate measured scientifically (thinking hard about consulting a doctor these days) because its not so simple for everyone. Plus no one loses 10 lbs in a year by cutting out something small.

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    • Emily,
      Your situation sounds like mine, except I am older (52). Please consider that you can’t out-workout a bad/excessive diet. I went from a bad diet to a good one, with no results. I finally figured out that my 2000 calorie per day health diet was actually over 3000. No wonder nothing happened, even when I tried hitting the gym more. I have learned that you have to weigh all the food that you consume where you don’t know the calories, and you must track all calories every day. It sounds hard, but it’s not. You only need a cheap digital kitchen scale and an Excel spreadsheet. I’m certain you will find out that you are consuming way more calories every day than you think you are. You can’t eyeball it, or guess. You can’t do this math in your head either…. trust me it doesn’t work. I track calories daily and work out minimally and am losing weight much faster than I thought possible. My workouts will increase once I get closer to my goal and reduce my 20% calorie restriction to 10% or less. I’m down 25 pounds in three months and have 13 pounds to go. And I’m never hungry with a 20% restriction. Minimizing refined sugar products is a must. Eat more protein and healthy fats, no sugary drinks, plenty of water and good sleep. It works great.

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  12. This issue just depends upon how you look at it. It is 100% accurate that if you cut 3,500 calories, you will be one pound lighter than you would have if you didn’t. But it’s also not that simple, the body is smart and the brain is dumb. If you cut some sweetener from your coffee, it is likely that you will have cravings and make up for it somewhere else. In that case, you will not have cut the calories and it does not invalidate the original statement. Excercise makes you hungry and you eat more. 100 calories of protein fills you up more than 100 calories of carbs. But that does not mean that 3,500 calories is not 3,500 calories. It just means that it is more difficult than you think to truly burn 3,500 calories.

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  13. Rules like these are quite nonsensical, even after a cursory examination. Without focusing on the particular number, thinking that a person with a BMI of 22 and BFP of 14% will lose the same weight after reducing their caloric intake by 3500 kCal as a person with a BMI of 29 and BFP of 34% is almost insane. Some people will require more and some will require less, to lose certain weight and maintain a given weight level. A percentage of TDEE rule might be better suited, given the numbers I’ve seen (e.g. – about 20% of TDEE seems to work across a wide range of BMI/BFP).

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  14. Certainly different people have different metabolisms, however, from my understanding, the article mis-explains “extra calories” and what they are (as evidence by the assumption that there is an exponential gain).

    It is 3500 calories more than what sustains your current weight. For example, if you weigh 150 pounds and do no exercise, live a very sedentary life, you need about 2000 calories per day to maintain that 150 pounds. But if you eat 2500 calories per day, you’ll gain weight up until what 2500 calories per day for a sedentary person supports, and then your weight gain will stop.

    By the representation in the article, it goes like: if you ate an extra 100 calories per day, that means you’d be going from 2600, to 2700, to 2800 and etc. If that is how you ate, then you’d gain weight forever — eventually you’d be eating 10000 calories per day. But if your goal weight is 150 pounds and you eat an extra 500 per day, you’ll weigh up to about 240 pounds and after that, you won’t gain anymore weight because 240 pounds is what 2500 calories per day for sedentary person supports (but if you were active, exercising frequently, then you’d need 2900 calories per day to support 150 pounds. What you eat is important by even something like cycling for an hour or two per day is going to use a large chunk of calories).

    That “extra calorie” is relative to your weight. If you eat 2500 calories per day and you weigh 240 pounds, and are totally sedentary, you’re not eating any extra calories per day, even if your goal weight is 150. “Extra” must be understood as being relative to your current weight.

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