[slight hijack, but related to the topic]
Well, I have some raw data handy. I’ve been on a “diet” (really more of a lifestyle change) for the last 120 days (so far!). I’m kind of a control-freak technologically oriented person, so I’ve been able to stay on program/motivate myself by precisely tracking calories in/out.
I’ve been using www.fitday.com - a great (free) website that allows you to track calories consumed, and provides a pretty good estimate of calories burned. I also made myself a basic spreadsheet in excel to track my daily/weekly/monthly progress and calories in/out.
For calories consumed, they have a pretty comprehensive food database. You can also add custom foods by manually entering information taken off of food labels, or other nutritional information/databases on the internet.
Most relevant to the discussion at hand - I’m pretty sure that their nutritional values are based on how many kcal your body actually extracts from the food - for example, kcal from carbohydrate is grams of carbohydrate MINUS grams of fiber, multipled by four kcal per gram. This is because fiber is pretty much indigestible.
For calories burned they use a formula which takes your gender, height, weight and general activity level into account. You can also add activites that you do each day, and their intensity/duration, and based on your height/weight it calculates how many kcal the average person your size would burn doing that activity and adds it to your daily total.
Obviously there’s some estimated involved, particularly with the kcal burned equations. And I’ve been very meticulous in recording everything I’ve eaten every day. The results have been pretty accurate.
In my case, I’ve been watching what I eat for 120 days. I started at 270lbs, and am currently at 245.8lbs (as of this morning). My average calorie deficit each day has been about 741kcal (total deficit over 120 days of 88,909 kcal). There are about 3,500 kcal per pound of weight loss (fat). So my calculated weight loss should be 25.4lbs, and it’s really been about 24.2lbs. That’s a pretty darn accurate estimation.
I realize micro-managing calorie input/output isn’t for everyone. But it’s working pretty well for me. And all of the nutritional information that my tracking is based on is either taken directly off of food package nutritional labelling, or the same information online. So obviously, the food labels are fundamentally pretty accurate.