Whilst in principle this is off course, correct, there is so much more to this energy balance equation than we realise. And its a great start but we can look at many other factors that play a part in messing up this equation.
With regard to the ENERGY IN:
Did you know that food labels can be up to 25% inaccurate?? So you can't rely on the calories listed on packaging at all.
And did you also know that the amount of energy in a food isn't necessarily the same as what we actually absorb?
That's right. We get less energy from minimally processed carbohydrates and fats than we do from processed ones. And we burn more calories digesting those minimally processed carbs & fats too. In fact, as an example, you absorb 38% less energy from whole peanuts as you do from peanut butter!
We also absorb more energy from cooked food and/or soaked, blended and chopped food.
Finally the amount and type of gut bacteria also affects how much energy we absorb from our food - and we are all different in that regard!
So with regard to ENERGY OUT:
There are a few considerations;
1. Resting metabolic rate (RMR)This is the energy used to just live, before you even get up out of bed. i.e. the energy for your heart, lungs, kidneys to function. This take 60% of your energy out and depends on your weight, sex, age, body composition and genetic makeup
2. Thermal effect of eating (TEE) yes 5-10% of your energy expended is taken up with just digestion. And the digestion of protein burns more than any other macronutrient.
3. Purposeful exercise (PE). This depends on intensity, duration, your body weight, sex etc too
4. Non exercise activity thermogenesis (NEAT). These are the calories you burn by going about your daily business, figitting etc.
SO the thing to know is that if you try to outsmart your body by messing with any of the above, it will almost certainly outsmart you back!
For example, if you consume less calories, your energy expenditure will drop so you will burn fewer calories in response to eating less, and vice versa.
This might explain it better:
Eating less causes TEE to drop
Weighing less causes RMR to drop, also PE calories burn to drop
It also causes NEAT to drop.
Finally the calories NOT absorbed drops and you absorb more of what you eat.
Which results in a lower rate of weight loss than you would expect.
So dieting doesn't damaged your metabolism, but because of the adaptations your body goes through in response to repeated fat loss, energy expenditure is always lower than people who have always been lean.
Look out for our post post on the best strategies for losing fat and keeping it off