One of the most common obesity myths (propagated in countless publications and statements) is that it only takes a small daily caloric excess to put on vast amounts of weight over a lifetime. Thus, it is often said that eating as few as 20 extra calories a day, resulting in around 7000 extra calories per year, will add up to approximately one kilo annual weight gain, which, if continued over decades, can add up to tens of kilos of extra weight.
However, this calculation is far too simplistic, because as the body gains weight, its energy requirements also increase. As soon as the body’s daily energy requirements increase by 20 calories, there is no longer any caloric excess and so weight gain stops. To continue gaining weight, you would need to now add another 20 extra calories which will in turn increase body weight till those too are just enough to meet increased demands, at which point you would need to add another 20 calories to keep gaining weight.
In other words to continue gaining weight, it is not enough to simply eat 20 extra calories per day and hope for the best - rather, the amount of extra calories has to keep increasing to sustain weight gain over time. This means that you would soon need to be eating 100s of extra calories per day more than you were eating before you started gaining weight just to maintain the same rate of weight gain.
This simple physiological truth is now once again explained by Martijn Katan and David Ludwig in a brief but enlightening article published in JAMA.
Using simple examples, Katan and Ludwig illustrate that for most people to move from a BMI of say 25 to a BMI of 35 actually requires 100s of extra calories per day (in the 300-500 cal range). Because of the natural growth and ever increasing caloric demands in children, the daily energy excess required for kids to become obese is even greater (in fact 500 to 1000 extra calories per day for young children).
Sadly, for exactly the same reasons that weight gain for a given caloric excess is “self-limiting”, so is weight loss for a given caloric deficit.
This means that a given reduction in caloric intake (let’s say eating 500 calories less per day) will only result in weight loss for as long as it takes the body to decrease its daily caloric needs by that amount. Unfortunately, this generally occurs within a few weeks of starting your diet (as the body loses weight and hormonal changes kick in to reduce energy metabolism). This is when you stop losing weight, despite still eating 500 calories less than before. To start losing weight again, you would now need to reduce your calories even further, but even then weight loss would once again stop as the body adjusts to even fewer calories. (This is why people who have bariatric surgery, despite consuming far fewer calories than before, don’t simply continue losing weight till they disappear).
Thus, in the same way that continued weight gain requires relatively large net daily increases in calories (albeit in progressive steps), so does continued weight loss require huge caloric deficits to be maintained over time.
The commonly promoted myth that small changes in energy intake will eventually lead to large gains or losses in weight over time is simply wrong.
Indeed, it is exactly because gaining or losing large amounts of weight takes a considerable caloric excess or deficit that has to maintained over time, that weight management is so difficult.
If small changes could make huge differences, we would not have an obesity epidemic.
AMS
Edmonton, Alberta
Hat tip to my colleague Geoff Ball for pointing out this article
In The News
January 7th, 2010 at 8:38 am
I totally agree with your assessment, particularly with regards to weight loss. As the metabolism slows it becomes increasingly difficult to lose weight at the same rate (or even at all).
I think this highlights the need for resistance exercise to maintain muscle mass during weight loss. Recently I encountered one woman who lost 50lbs and approximately 20lbs of that was measured to be muscle loss. Her metabolism had slowed dramatically and she had reached a weight loss plateau. She did no exercise.
Another woman on the same nutrition plan lost the same amount of weight, but only 3lbs of muscle were measured to be lost. She continued to lose weight at a steady rate and felt fantastic. Her routine included 3 days per week of cardiovascular exercise and two weight training bouts per week.
Obviously, this is not a large sample, but certainly an example of how exercise can work to prevent slowing of the metabolism.
Also, as I’ve mentioned before, bodybuilders often use full day high calorie and high carbohydrate “refeeds” to elevate leptin and maintain their high metabolisms. Whether this truly works has yet to be measured by science, but there is no doubting their success. Just an idea to ponder.
January 7th, 2010 at 12:08 pm
I don’t quite understand. I get why adding 100 calories won’t cause someone to continually gain weight. Eventually, the body gains mass until those once extra calories are needed to maintain the new size? And then someone would need to consume additional calories (more than the original 100) to gain any more weight. So why couldn’t a small but steady over the long-term increase in intake cause weight gain?
As for the weight loss, again I understand that there is a metabolic effect where people who lose weight have metabolic slowing even greater than can be accounted for with mass loss. However, from what I have read I understood it to be in the range of maybe a few hundred calories. Is this not correct? And is the amount of this slowing related to the severity of the restriction? If someone who normally might need 2600 calories to maintain their weight, starts eating 2100 calories per day will it really only take a few weeks for the body to drop their metabolic rate by 500 calories each day? Has this been found in metabolic ward studies?
I don’t disagree with the main point that assertions that cutting out or adding a small amount of calories each day will lead to long-lasting body changes are wrong. Nor with the idea that weight-loss is made difficult by metabolic shenanigans. I’m just trying to sift through everything I hear from all sides. Also, I’ll admit to totally non-scientific interest in that I’m someone who’s lost a little over 80lbs by employing small changes over time. But I’m still eating over 2000 calories every day. I could just be an outlier though.
January 8th, 2010 at 1:55 pm
While I do understand this blog is meant mainly for doctors I really find this post one of the most depressing things I have read in a very long time. Is there no hope but surgery?
January 8th, 2010 at 5:48 pm
Your caloric density for weight gain/loss does not match the records. The typical value is 4.0 gm/C, not 7.0 gm/C for long term changes.
January 8th, 2010 at 5:51 pm
make that C/gm
January 11th, 2010 at 7:31 am
Philisophically speaking, adding five small “100 calorie deficit changes” could cumulatively add up to that significant 500 calorie deficit. So if one were not looking for immediate weight change, but started applying these strategies (in combination, perhaps, with an increase in calorie expenditure through intentional exercise or incidental movement, i.e. an active commute), over time, these could lead to weight loss. I think that if the goal is people whose overall health is improved, not only temporary reduction in weight, that finding those areas where the calories are not missed (for some, this might be switching from drinking regular soda to drinking iced tea with artificial sweetener, for example) and areas where adding in movement actually improves quality of life (dancing, active commuting, participating in sports) could make a difference in weight, over time. These changes could be cumulative.
This is in part why I think a “Health at Every Size” approach can lead ultimately to a reduction in weight. Not for weight loss as a goal, but as people are no longer in a resistant or oppositional stance (a very human response to discrimination). When approached with compassion and benificence, changes to eating and movement habits that have merit for their own sake, not only for weight loss, can then be adopted.
As a woman, I have a higher risk of developing breast cancer than a man does. Would gender reassignment surgery be an appropriate strategy for combatting breast cancer? I think becoming someone who is thin would require just as dramatic a change — and would not benefit my overall long-term health. But incorporating activities and action into my life that have meaning and value beyond weight loss are worth doing, not because they make me thinner, but because they make me “more me.”
September 3rd, 2010 at 3:28 pm
The basic physics of fat loss is “calories in - calories out = fat.” The assumption here is that excess calories become fat. That assumption has yet to be overturned by evidence..Anyhow, Nice piece of information.
December 21st, 2010 at 6:25 am
In my clinical practice with obese patient or normal patient who don’t want developed in obese, I simply use the negotiation methods, more calories for more physical activity daily at least two hours for losing weight. Alerting the obese person the exercise must be progressive, 30 minutes at the beginning.