Busting the 3,500kcal = 1lbs Weight Loss Myth! A Scientific Deconstruction of a Dumb Rule of Thumb Reveals that Women Need More, Men Less Than the "Rule" Predicts

Image 1: If you are still putting your Happy Meal on a scale, you should not wonder why your weight loss falls short of your "calculations" - especially if you happen to be a woman (img. elementsofwellness.com)
While I would hope that most of you have by now embraced the notion that a calorie is not a calorie (at least, when it comes to nutritional calories), I suspect that one or two of you have still just been reviewing how much "calories" they have already eaten, or how much "cardio" they will have to do to compensate for the piece of pizza they are going to eat tomorrow at a friends party... > "STOP!" < this is what you should tell yourselves whenever thoughts like that are passing your mind (well, unless you are in the end-stage of your prep for a bodybuilding contest, I guess ;-) After all, a very recent study that is based on the results of two large-scale weight-interventions (Heymsfield. 2012), i.e. the CALERIE study, conducted at the Pennington Biomedical Research Center and the Kiel study, which was named after the German town Kiel, where the 13-week weight loss intervention took place, confirms the fallacy of number games like that.

A physicists would know: A pound of fat weighs 500g, not 3,500kcal ;-)

In order to establish the "actual" energy deficit that was necessary to elicit the loss of 1lbs of body weight in the 98 obese subjects in the CALERIE and the Kiel studies (average initial BMI of ~35 (25-43) kg/m²; mean age of ~38y and ~34y for the female and male participants, respectively), Steven B. Heymsfield and his colleagues (re-)analyzed the detailed nutritional and weight loss data from the studies and came up with the more or, I should say, less surprising result that the still widely accepted rule that a caloric deficit of 3,500kcal would result in a 1lbs reduction of body weight has to be revised ...
Figure 1: Energy deficit (in kcal) that was necessary to shed 1lbs of body weight at different time-points (in weeks) of the -25% reduced energy intake and the 890kcal/day arm of the CALERIE study (data adapted from Heymsfield. 2012)
If you take a closer look at the data in figure 1, which shows the actual amount of energy (in kcal) that was necessary to shed 1lbs of body fat, it becomes obvious that there was actually not a single time-point in the 24week dietary intervention, when the men and the women on the -25% (figure 1, left) or 890kcal/day (figure 1, right) both lost 1lbs of body weight per 3,500kcal.

Women have a harder time losing weight than men, but retain more lean tissue

If we go by the logarithmic regressions (red and blue lines; coefficients of determination see figure 1), the following important trends become obvious:
Figure 2: (a) increase in calories necessary to shed 1lbs of BW from week 1 to week 24; (b) average calories necessary to shed 1lbs in men and women over the whole study period (data adapted from Heymsfield. 2012)
  1. Independent of the degree of calorie reduction (low calorie = -25%; very low calorie = 890kcal per day) and the sex of the subject, the caloric deficit that was necessary to shed 1lbs of body weight (not fat!) increased from week 1 to the end of week 3 (cf. figure 2, a)
  2. Both, the baseline, as well as the gradual increase in calorie reduction that was necessary to shed 1lbs of body weight in the course of the 24d study period was greater in the very low calorie arm of the CALERIE study (cf. figure 1 and figure 2, a). This, btw, is clearcut evidence for the fallacy of starvation diets.
  3. On both diets, women had a significantly harder time losing weight than men. This was even more obvious in the low calorie (-25%) than in the very low calorie arm (cf. figure 2, b).
In that it is also important to note that the relation of fat free mass to total body weight loss (ΔFFM/ΔBW) was maximal (60% for men and 50% for women) at the beginning of the study, had a nadir after about 15 weeks (~40% for men and ~20% for women) and showed a trend to increase again at the end of the 24 week study period of the CALERIE study. In other words, while women have a harder time losing weight, they maintain more of their lean muscle mass, than men do. A results that was, at least with regard to total weight loss, supported by the results of the Kiel study (no data on body fat / fat free mass loss available).

My advice: Forget about the rule of thumb, about calories and body weight!

Other than Heymsfield et al. who obviously still believe that it will by whatever means be possible to calculate the exact amount of calories to shed 1lbs of body weight, my take home message from the results of this study is that all the calorie counting, the daily disappointment, when you step onto the scale and the notoriously unreliable dietary rules of dumb... ah,  pardon "thumb", are something you banish from your weight loss inventory, right away.
Feel lost without your calories? Don't know where and how to start? Afraid of throwing the scale out of the window? Then it's time to (re-)read the Intermittent Thoughts on Stocktaking, Goal Setting, -Tracking & -Resetting to Achieve a Healthy Weight & Shed Excess Body Fat
A food log, where you record food and not calories  (I mean I still eat food, you know, things like eggs, butter, a steak, potatoes... those things without nutritional information on it!), a general understanding of the macro-nutrient (fats, carbs, protein) ratios in those foods and a measuring tape to access your progress, is all it takes access and adapt your food (not energy!) intake and evaluate the success of your diet (which does not equal weight loss!)... and I guess I don't have to tell you that the results of the very low calorie (890kcal) arm of the CALERIE study clearly suggest that dieting on a single cup of broccoli and a single serving of chicken breast sprinkled with some olive oil, is not an option, regardless of your sex, do I?
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