Discrepancy in TDEE calculations

Question

After a (very) dirty bulk, I have now been losing weight for about 39 weeks. (It has been going OK.) At the start of my diet (at the end of November, 2015) I was about 110 kg. I planned my weight loss proces to be slow and long, so as to maintain as much muscle as possible. As a guideline, I used several 'total daily energy expenditure' (TDEE) calculators to find a baseline for my diet. All of the calculators I used gave me a TDEE of about 3,000 kcal. (Of course, including exercise, cardio, etc.) I eventually cut down to a weekly average caloric intake of 2,500 kcal per day. This, given the calculated TDEE level of 3,000 kcal, should be an average deficit of 500 kcal per day, which was the deficit I was looking for, and planned to maintain for as long as necessary (until I was happy with my bodyfat level).

At the time of writing (late August, 2016) I am about 90-91 kg. Suppose for the sake of simplicity that I have now lost 20 kg, since the start of my diet. That is an average of about 0.5 kg per week, which is fine. Assuming the '3500 kcal per pound of body fat' rule is true, and that my weight loss has been mostly due to fat loss, we can calculate that my daily caloric deficit should be around 500 kcal (it is actually more like 560 kcal).

Using 'myfitnesspal.com' I have logged my daily caloric intake and expenditure due to cardio carefully. Over the course of my entire diet I have calculated that my average daily caloric intake is about 3,000 kcal. Taking the above calculation into account, that would give me a TDEE of about 3,500 kcal.

Where does this discrepancy come from? On the one hand we have a TDEE of 3,000 kcal, based on age, weight, height, 'activity level', etc. On the other hand, we have a measured TDEE level of 3,500 kcal. How can this difference be explained? Is it common that the online calculators are this inaccurate? Or is it simply because my measurements (e.g. actual caloric content of food may not be as said on the package, caloric expenditure due to cardio may not be as calculated by the treadmil) are too inaccurate?

As some added information which may be important: even though my measured average daily caloric intake is about 3,000 kcal, this is not actually the amount of calories I ate daily. During weekdays I would always eat around 2,500 kcal per day. On training days this would make a net intake of 2,000-2,200 kcal, depending on the amount of cardio I did that day. During the weekend I would then 'cheat' (not really, because it was incorporated as part of my diet) by eating a lot more. The amount of calories I ate during the weekends would vary a lot; sometimes it was around 3,000 kcal, sometimes 4,000-5,000 kcal or more. Could the discrepancy be explained by the erratic daily caloric intake? I can imagine that the weight loss by such an erratic eating pattern would be different than for a diet where the caloric intake is exactly the same each day.

Thanks in advance!

Answer 1

First of all the discrepancies doesnt stem from one single factor; all of your suggestions for explanations of the discrepancie are a part of the puzzle.

With that said the major source is probably the TDEE estimate. The discrepancie from the TDEE estimate might stem from you being an outlier, it might be that your intepretation of activity level differs from the authors (creators) of the calculator, and so on.

Caloric content listed on the package is usually very accurate, as it is strongly regulated (depending a bit on which country you live in, what companies that produced it and so on).

Regarding your last note on splitting the kcalories unevenly around the weak; this might affect your NEAT (Non-exercise activity thermogenesis). To put it simple, if you are not feeling especially hungry during the days you eat little, so that it doesnt affect your energy level and thus almost "subconscious" activity, you will burn the kcalories the calculator says you are supposed to during that day. If you simultaneously feel extra energized on the days you eat more, and thus move around more (at random) you will use more kcalories than the calculator suggests. Normally the effect of distributing your kcalories on NEAT evens out over a week, but it doesnt have to be so.

Answer 2

Lies, darn lies and statistics...

There are a half a dozen formulations of the TDEE calculation, which yield numbers that vary by as much as 17%, between formulations. Add to this the notoriously inaccurate KCal counts on food packaging, which legally only need to be within ±20% of the an Atwater estimate, which in turn is approximation, and things are muddled eg.

• Calorie Labels Inaccurate, Experts Say
• Daily Mail - Calorie counts on food labels could be inaccurate by up to 50per cent as they rely on 100-year-old calculation method
• Food Label Accuracy of Common Snack Foods

And you're left in a position where any numbers churned out need to be taken with a large, 0 KCal pinch of salt. A 500 Kcal daily arithmetic error in quite possible.