You should probably be lifting weights

If you're reading this you should probably be lifting weights. Nothing will have as profound an impact on your physique, body fat levels, and overall health as resistance training (besides nutrition of course!)

One often forgotten benefit is increasing bone density, which becomes incredibly more important as you age. Bones are metabolically active tissues, the denser your bones are, the more metabolically active they are.

Resistance training provides stimulus to our bodies, that our bodies then in turn activate various processes that create adaptations to that training stimulus. This is what grows muscle, makes bones and connective tissue denser, and creates neural adaptations so the next time we expose ourselves to a similar stimulus we're better adapted to handle it.

These processes occur over the hours and days after a training session and cost energy, thus we expend calories to "do the work" to create these adaptations. Nothing in our bodies happens for free, all work done requires energy, and our energy currency that our bodies operate on is calories.

While long bouts on the treadmill, stairmaster, going on jogs, and HIIT sessions may produce larger caloric spend than a weight lifting session in the short term, our bodies are smart, and can relatively quickly create a different type of adaptation to these to expend less energy. It gets more efficient, and when it comes to caloric expenditure the goal is for our bodies to be as inefficient as possible. When we have an efficient metabolism our bodies adapt to do the same with less resources, which makes losing fat harder and gaining it easier. 95% of us want quite the opposite.

If we always only do a 15 minute treadmill session, what once produced say 100 calories of expenditure will produce marginally less and less as your body adapts. So to continue producing a 100 calorie expenditure you will need to spend more and more time on the treadmill (or increase the intensity.)

Similarly, with resistance training, 3x10 of bicep curls at 20 pounds will only produce so much adaption in hypertrophy and strength. If you only perform these same 30 reps at 20 pounds for months on end your progress will stall. This is why progressive overload is the holy grail of lifting weights to continue creating neural, hypertrophic, and strength adaptations.

I'm not here to say you should completely quit doing all forms of cardio, or HIIT and they are worthless. These are tools that can be included to further accelerate caloric expenditure generally when in a caloric deficit created primarily through means of your nutrition.

Having a sound approach is much more than half the battle when it comes to effective training and nutrition.