Is calories in vs calories burn't a myth?

You certainly don't know how many shots of whiskey she knocks back at 2am.

I've always believe calorie in vs calorie out to be true. After working out my base metabolic rate and counting calorie deficits , my weight loss adds up and the sums work. However, my grand mother for example only eats around 1000 calories a day and has done for the last 20 years. How come she doesn't starve to death? She is more active than me throughout the day so it's unlikely that her base metabolic rate is much lower than mine.

Also how do you explain people on a CRON diet? Surely they would lose weight until there was nothing left to lose if calorie in vs calorie out was a sound concept.

Don't want to overcomplicate anything as it works for me Am just naturally curious

It's not a myth. The problem is that people really have a poor idea of how much they eat, even if they log. People also have a poor idea of what they burn. TDEE and BMR calculators are just estimations. Even a heart rate monitor is not 100% perfect. We also don't know what percentage of what we burn is glycogen, fat, muscle, etc. So if you have an imperfect calorie count + an imperfect TDEE combined with the fact that we don't know what our body is using for fuel and the fact that weight loss isn't linear due to water retention, glycogen saturation, etc it can seem like CICO doesn't add up. In reality it does, it ALWAYS does.

In the long run, if you truly eat less then you burn in a day, weight will go down. It will, for the reasons above, RARELY correlate exactly with how much you THINK or have calculated that it should go down.

I doubt the accuracy of your grandmother's estimating acumen.

CI/CO is not negated by one old woman's inability to be accurate.

To all the people saying CICO is much more complicated then it seems, I tend to disagree. While there are indeed a tremendous number of factors that play a role in the calories out side of the equation, It is my opinion that upwards of 90% of the people that struggle with CICO do so because they can't get the calories in side right. Your average Joe has no idea what they eat. None. Zilch. Nada. Your average MFP user has a better idea then than Joe but I still think most users here are poor calorie counters. What I see most often is people not using food scales, estimating portion sizes, having unaccounted for cheat meals/days, and eating out pretending that the nutritional information provided by companies is accurate. Chipotle isn't using a food scale, the chef at your favorite restaurant doesn't start the dish over if he/she accidentally adds in to much butter or oil. Then there is the biggest insult to the calories in side of the equation, the FDA. Even if your count is perfect (which it isn't), you never cheat or forget (which you know you do), and you weigh 100% of everything to the gram on a scale, the FDA lets companies legally do a F**kton of rounding. Kiss your sweet, perfect, calories in number goodbye.

I personally have had tremendous success with calorie counting but even I make mistakes on a semi-regular basis. I forget to log things here and there, I also go out to eat or eat meals that friends/family have prepared. If at any point I am not losing weight over the long run, despite being confident that my calorie target should be well below my TDEE, I do not immediately jump to the conclusion that the calories out side of the equation is wrong. My metabolism isn't broken, my thyroid is fine. I know that the most likely problem is the calories in side of the equation. If I think I'm eating 2500 calories and I'm really eating 3000 then the best bet for me is to eat what I think is 2000 and hope what it actually is, is below my TDEE. This is why this website has 100's of people who can't lose weight on 1200 calories. There isn't a rash of people with under diagnosed metabolic conditions, there's a rash of over-eaters who don't realize they are over-eaters.

While I of course concede that there are rare examples of people with true metabolic disease, and that certain factors can lower the calories out side of the equation, the equation is ALWAYS at play and losing weight is never more complicated then eating less and moving more. How much less and more varies greatly but it's still ALWAYS the answer.

@vismal This makes sense to me actually.

Is it possible that a metabolism adjusts to a lower calorie intake? Or is that just complete BS.

It is surprising that different people's BMR's or required calorie intake can be so far apart. Is this the reason it is possible for some people to be able to eat massive calorie surplus without putting on weight because really it technically isn't a surplus but a variety of different factors such as a fast metabolism/ high energy requirements. If this was true it would stand to reason that their is such a thing as a fat gene and skinny one...

People's metabolisms are vastly different for many many reasons. Genetics play a huge role. Also people who are very active simply burn more calories a day via their activity. When you diet for long periods of time you can have some slowdown to your metabolism. It's never going to be enough to make weight loss stop or cause weight gain. Anytime you are not losing weight in the long run when you think you are in a deficit you need to examine a few things. More often then not you are simply eating more then you think. I would say 80% of the time this is the case. Other times people, sometimes unconsciously, become less active during prolonged deficits. Both these examples still fall within CICO. To sum it up, if you aren't losing weight (again in the long run), you're eating too much, you're burning too little, or both.