Your weight is a side effect of whether or not your body is healthy. If your body is underweight, you aren't getting enough energy and nutrition to keep up the demand. If your body is overweight, you are eating too much food that lacks nutrition, which causes your metabolism to slow down, your hormones become unbalanced and create inflammation, your stomach pH becomes more alkaline, your cells reject nutrients, and you store water and fat because your body cannot utilize it anywhere else, so it packs it away for use "later", like a fridge.
Metabolism all boils down to basically these things:
The calories you consume each day
The type of calories you consume (sedentary people should not eat excess carbohydrates, that creates insulin resistance and a plethora of metabolic diseases overtime, and your body converts the unused carbohydrate energy into adipose tissue)
Your activity level (more activity burns more calories)
The type of activities you do (aerobic vs anaerobic)
Your lean body mass (muscle requires more energy to maintain than fat, more muscle = more calories needed)
The amount of vitamins, minerals, trace minerals and phytonutrients you take in (sodium, potassium, magnesium, zinc, vitamin A from meat sources, D from sunlight, K2 from vegetables, etc)
The pH of your stomach (stomach acid needs to be acidic in order to properly break down and assimilate proteins, vitamins, minerals and phytonutrients from your food, support a healthy GI biome for your gut bacteria, and eliminate unwanted foreign bacterias, viruses and pathogens... an alkaline stomach cannot work properly and leaves you with various issues such as gas, bloating, cramping, brain fog, heartburn, and more)
The condition of your liver (the liver handles a lot of processing for everything you eat, and can only tolerate a certain threshold of fructose and sugars... any excess will cause the liver to accumulate fat (and cause non-fatty liver disease) and will convert to adipose tissue)
Hormone balances (high levels of cortisol, insulin, bad estrogens, etc. will cause you to store fat, decreasing those with a proper diet, exercise, and good quality sleep is key)
By fixing these, your metabolism will improve. My metabolism is much higher now that I'm in my mid-20s, I eat a balanced low carb diet, exercise regularly, supplement things like ACV and vitamins/minerals that I don't get enough of from my diet, and I can eat much more than when I was a teenager.
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"Your flesh is a relic, a mere vessel. Hand over your flesh, and a new world awaits you. We demand it."