I can totally buy calorie surplus being the factor that causes weight gain. BUT what is it that causes different people to burn/partition calories so differently?

Two different conditions that cause out of control weight gain on low calorie diets are thyroid disease and Cushing's syndrome.

In uncontrolled type I diabetes isn't there uncontrollable weight loss?

Inflammatory conditions, autoimmune conditions, nutrient deficiencies, hormonal imbalance are some variables that cause people to use calories differently than others and thus gain/lose weight differently.

No, I don't think so.

Its simply wrong. Everybody knows bunch of people who eat like crazy and are always fit and vice-versa.

The fact is that you can't look at the humans as simple fuel machines. We have many systems that can be ON or OFF depending on the status of the body defined by circulating hormones. So, for instance, reproductive system takes some energy, and if its down for some reason that energy could be shuttled to adipocytes.

She is generally right, but it doesn't really mean anything since we don't know how the energy is distributed. Its the same as saying for instance, that if you want to be rich, you need to get million dollars. That doesn't tell you how to do it, nor how to deal with eventual problem that somebody is constantly stealing from you despite you work as hard as other rich people.

The calorie in calorie out is probably the most trivial and stupid explanation of obesity I ever heard. Its hardly any better then proposing that there are elephants on mars doing curse on you.

i don't get the question.

it depends on from where you looking at it from. from 10k feet, everyone gains weight because of some kind of energy balance issue. call that the macro-mechanism, i guess. the means by which that energy balance get thrown off varies greatly.

I would wager that all omnivorous mammals gain and lose weight by the same mechanisms. Depending on how you look at it, you could extend that out to all mammals and maybe further. Differing endocrine profiles affect energy partitioning of course (which mostly tracks along gender lines in healthy individuals), but the underlying mechanisms involved in gaining or losing fat are the same.

Edit: Even with your edit, I would still say that a net gain in adiposity is the result of more FFA being esterified in adipocytes compared to how many are released and oxidized. This would apply to all animals and of course both genders.

Edit2: To clarify, I mean the net FFAs stored/released as viewed over time, since adipocytes have a huge amount of transmembrane flux that increases as they increase in size.

This question should be clarified. As it's written, there are a couple of ways to interpret it. And most of them don't make any sense.

Ohhh. No, I don't think weight gain and loss have the same factors at play, and I do not think calories are the main factor within reasonable perimeters (for instance, 99% of people will see quick weight changes on 300 calories per day, or 10,000).

Also fat gain and loss is totally different, metabolically, than muscle gain and loss and that can't be discounted when we're talking about bodyweight in pounds.

It seems to me it's not a numbers game with the calories but the calories themselves. 2000 paleo calories don't equal 2000 SAD calories. What would happen to Mr. Quilt if he started eating 1500 calories a day of Krispy Kreems, instead of his usual 1500 calories of coconut oil? (assuming he eats 1500 cal of CO)

Also, go to any Atkins Forum, there you will see countless posts from people who are back into Atkins for the nth time as they fell off the wagon and gained all their weight back plus. You rarely read those type posts on Mark's Daily Apple.

Why do I feel like this is a pop quiz? Whew, good thing I studied. Um, no, calories in, calories out is ridiculous at best, and a really mean and dangerous way to torture overweight people dealing with inflammation and thyroid conditions at it's worst.

I might consider it if people didn't poop, but we have these lovely digestive tracts that remove anything we don't require for energy from our bodies. So, if you to wayyyy overshoot your food intake, you'll poop more, but that is about it, your body will take what it needs and excrete the rest.

If I only ingest a small amount of food, but that food is inflammatory to my body it'll bloat right up. I can prove that if I readopt my old starvation diet of living on 2 scones and 4 8oz. nonfat lattes per day. It really helps pack it on if you avoid sunlight at all costs and have an undiagnosed thyroid condition too. I managed to gain 30 lbs. I didn't want in 2 months.

I may be an oddball, but I have starved myself fat, and feasted myself thin several times. So the math of "calories in, calories out" does not seem to work for me.

Quantification of the effect of energy imbalance on bodyweight

Dr Kevin D Hall PhD a , Gary Sacks PhD b, Dhruva Chandramohan BSc a, Carson C Chow PhD a, Y Claire Wang MD c, Steven L Gortmaker PhD d, Boyd A Swinburn MD b Summary

Obesity interventions can result in weight loss, but accurate prediction of the bodyweight time course requires properly accounting for dynamic energy imbalances. In this report, we describe a mathematical modelling approach to adult human metabolism that simulates energy expenditure adaptations during weight loss. We also present a web-based simulator for prediction of weight change dynamics. We show that the bodyweight response to a change of energy intake is slow, with half times of about 1 year. Furthermore, adults with greater adiposity have a larger expected weight loss for the same change of energy intake, and to reach their steady-state weight will take longer than it would for those with less initial body fat. Using a population-averaged model, we calculated the energy-balance dynamics corresponding to the development of the US adult obesity epidemic. A small persistent average daily energy imbalance gap between intake and expenditure of about 30 kJ per day underlies the observed average weight gain. However, energy intake must have risen to keep pace with increased expenditure associated with increased weight. The average increase of energy intake needed to sustain the increased weight (the maintenance energy gap) has amounted to about 0·9 MJ per day and quantifies the public health challenge to reverse the obesity epidemic. This is from a very recent article in the lancet

I don't think that it is ever a given that if something causes a certain condition, doing the opposite of that something will result in reversal of that condition. If you fall out of a tree and break your leg, you go get it set and wear a cast, you don't jump back up into the tree to fix your leg.

It is more complicated than calories in -vs- calories out. Metabolic disorder will hamper weight loss but allow weight gain (until you reach a threshold of weight gain).

Allow me to play devil's advocate here with what I call Metabolic Mad Libs. If the hypothesis is that it's all hormonal (be it insulin or whatever), so raising said hormone = fat gain, lowering it = fat loss, the mechanism is the same even if one disagrees with CICO. Even Taubes, and Eades, and Westman (Atkins), and ... yes, Atkins himself, know/knew that weight gain does not occur absent an energy surplus, and weight loss requires an energy deficit. (True weight of interest = fat mass, not water).

As far as I know, the hormones altering appetite and energy expenditure (mostly leptin & thyroid, but possibly ASP as some recent studies I've discovered seem to demonstrate) are not affected differently with weight loss on LFHC vs. LCHF diets (although there's some evidence that LC negatively impacts thyroid -- my own n=1 experience is that my metabolism tanks and I become super efficient after long stints on LC).

Bottom line, metabolic adaptations seem to be indifferent to carb v. fat content of excesses or deficits. I've yet to see a study show significant differences in reduction in BMR with weight loss between the two extremes, and overfeeding studies seem to slightly favor carbs (as in insulin spikes are associated with less weight gain per calorie over maintenance).

Hormones and food type tend to influence fat distribution (and to some extent fuel partitioning lean v. adipose) more than fat gain/loss per se.

Genetic influences cannot be ignored. Some people overeat without reaching a sense of fullness, while others have appetites under control, regardless of whether you are following a Paleo or SAD diet.