It's not quite as simple as calories in must be less than calories out. Because the body has starvation-survival modes that might kick in if you just diet. Getting more exercise is important, even if it is only walking.
This is mythology.
Zero evidence for such a thing.
Here's why. If you are fat, you can not go into "starvation mode." Fat is food reserves. If you eat fewer calories than your body requires for a given expenditure of effort, it will smoothly switch to burning pure fat.
And you can live perfectly well on pure fat.
In healthy normal people organ function is not really impacted until you have nearly no fat left, and your body must switch to metabolizing muscle tissue.
Either way, trust me... if you stop eating... you will continuously lose weight until you die. No "starvation mode" will slow the loss.
Look at the slave laborers who were underfed and overworked to death in the nazi death camps.
Without food, and without being forced to keep a high level of physical effort... what happens is that starving people naturally stop expending energy... and that lowers their caloric burn. Lay in bed hunger striking, and yes, the rate at which you lose weight will slow compared to a person who is being forced to assemble munitions all day.
People who are still eating daily, but eating significantly fewer calories than they burn, will lose weight at the proportion of that underfeeding to the amount required by whatever weight they currently are.
If you are fat enough to require 2500 calories but only eat 1500, you will burn 1000 calories a day of fat.
However, as you get thinner you need fewer calories to support that weight. When you get to the point where 1800 calories/day would keep you at your thinner weight, and you are still dieting at 1500 per day... you will at that point only be burning 300 calories per day of fat.
That- and reduced activity, is why the rate of loss seems to taper off... not any mythical starvation mode.
But it is important to note that ALL diets ultimately fail. Because they are viewed as temporary... you PLAN to someday no longer be 'dieting'...
The most critical thing is to get it thru your skull that you are talking about a
permanent change in behavior.
The folks who keep looking fine well into middle age are the ones who LIVE with less food, rather than the ones who are implementing 'diet plans' as needed.
Look at your life and make a choice.
You really love that chip and dip enough to accept the man boobs?
You really gotta drink that much beer to deal with your day?
No one ever died from chip or beer deficiency.
One day I looked in the mirror and simply decided that no 'snack', no 'meal' was worth having to look like that... no 'treat' was worth having to hold my breath to tie my shoe.
I still ate the healthy food my wife cooked for dinner- and plenty of it... but I stopped with all the other snacking and lunching thru the day... I stopped raiding the fridge for the leftovers from dinner.
In 3 months I dropped 40 pounds.
And you know what? Not once was I ever truly hungry... By belly was mostly empty... but that is not the same thing as feeling weak from hunger.
Why? because my body was living off of pure lard. Like eating just the fat offa thick steak for every meal.
Other benefits? I no longer have GIRD... turns out a huge contributor to GIRD is the fact that you have FOOD in your stomach all damn day long.
Your GI tract actually runs a LOT smoother and a lot better with some air space between meals.
I weight-train regularly and can eat as much as I like.
That will change. Not only the amount of exercise, but as you age you will require fewer calories to maintain the same weight ( fewer cells operating at full function )
People who do not gradually reduce their food intake as they age will get steadily heavier.
