I’ve never believed this — only because my weight is so consistent and my eating is not. My body must have a way to regulate the absorption of calories from the gut. When I have some insanely high calorie meal, my body doesn’t necessarily absorb all the calories. This seems easy to measure, so I must be wrong. Or…
Also, weight gain/loss should be measured on a weekly scale rather than daily. You might feel like your eating isn't consistent but it could be on a weekly-basis. For example, you might barely eat one day but eat 3500 calories the next. That seems like inconsistent dieting but in actuality, they average each other out.
That's only one side of the equation.
It is a basically proven fact (and largely implied by physics) that `calorie intake - expenditure = net weight change`. That is pretty much beyond dispute.
It is also true that some things affect expenditure, and it seems likely that most people have a "set point" that your body attempts to return to. This is also almost certainly changeable, as people have managed to change it in the past. (And this is less surely true than other things known.)
So yes, it's entirely possible to eat "inconsistently" and not have net weight change, your body is probably subconciously causing you to eat less after you eat large meals, and vice versa. Or possibly causing you to expend more energy after large meals.
People locked in a box will not be able to cheat and will demonstrate this.
No, our digestive tracts are extremely good at extracting any and all usable calories from our food.
100% of the time, when someone makes this claim, they are mis-estimating either their intake or expenditure, or not tracking for a long enough time period to escape the error bars inherent in daily hydration variance.
To add to what someone else said, you probably ate below your threshold to be able to maintain your weight. You can't guess this, the only way to get an accurate ESTIMATE on how much you actually ate in calories is to measure. Even pros over/under estimate what they eat in terms of calories
What's harder to refute is the loss of weight due to calorie restriction which is mostly physics. This is what the gp is talking about.
“ Ultraprocessed foods — such as refined starchy snacks, cereals, crackers, energy bars, baked goods, sodas and sweets — can be particularly harmful for weight gain, as they are rapidly digested and flood the bloodstream with glucose, fructose and amino acids, which are converted to fat by the liver.”
The real “myth” of calories in = calories out is that it’s possible to do it by feel. It takes a lot of work and math, like spreadsheet-level, to actually track calories in and out. So even though it is physically true as a concept, it’s not a good weight management strategy for most people.
Sugary snacks don’t make you feel very full for their caloric content. So unless you’re literally writing down the caloric information on the wrapper and comparing it to your total daily activity, it’s easy to overeat.
The real myth is that you can track calories in and calories out.
How do you measure how many calories your body absorbs from the food you eat?
How do you measure your calories out, particularly your resting metabolic rate?
Here's a hint -- the body changes its resting metabolic rate in response to calories in! Probably! Unless you eat junk food, and then maybe it doesn't!
In practise you don't need to track the out because it doesn't change much per day. It's not easy to burn 200 calories but it's easy to consume them. That's why it's common to hear that weight loss happens in the kitchen.
It does require work to understand your particular body, and discipline to do it consistently. Which is again, why it is not a good technique for most people. Most people don’t have the time, motivation, or really the need to do what this woman (in the video) is doing.
Apps like Macrofactor do it for you. You just track what you eat and your weight.
One secret about using CICO is that you do not need to know the gut absorption rate! You just need to track the calories before absorption, the numbers printed on the box. Easy these days with a smartphone app. The measurement does not need to be perfect at all. It only has to be decent on average. You can have variable accuracy of 25% on any given food and still get well under 10% on average for a week. It doesn’t matter if there’s a bias either, if you track your weight. The reason absorption and bias don’t matter is because you’re doing science with a black-box (your body). Measure the known input, monitor the output. Do it for a long time and you’ll find the maintenance input. Track input above that and verify mass gain, track below and verify loss. The maintenance value you come up with will “absorb” and bias, and gut calorie conversion rate, and other inaccuracies.
Measuring output is easy with a heart rate monitor. Changing metabolism we already discussed, but important to know that the range of elasticity is like around 15%, and in practice for any give person may be lower. It’s not some massive factor you can’t predict, it’s within a narrow enough range for the majority of people, statistically, that you don’t need to worry too much. And it will be accounted for if you track calories and weight over a long enough time frame.
And here is a recent peer-reviewed article that summarizes the debate: Ludwig, D. S., Apovian, C. M., Aronne, L. J., Astrup, A., Cantley, L. C., Ebbeling, C. B., ... & Friedman, M. I. (2022). Competing paradigms of obesity pathogenesis: energy balance versus carbohydrate-insulin models. European journal of clinical nutrition, 76(9), 1209-1221.
Regardless of diet you will lose weight if you eat fewer calories than your body is burning. It will be harder if you eat junk food, but quite possible.
Just consider how much flatulence varies meal-to-meal, that's largely produced by calories guests living in your gut "burned" instead of you.
The trouble is it's a complex ecosystem hosting many lives, controlled by hormonal knobs affecting behavior/activity-level and energy storage, and the makeup of the food hugely affects how much is absorbed and at what rate.
Everyone knows firsthand when over-eating a massive meal of hard to digest foods there's a substantial amount of energy deposited in the toilet... And wild pigs / pet dogs don't get excited about eating human feces for lack of caloric value.
It's just an upper bound, nothing more.