What hair your parents have has a large play in what hair you will have, if your mum and dad both have curly hair that is thick as your school friend then chances are your hair will be thick and curly. This is not always fool proof but changing your diet won’t change your hair, using a different product won’t change the growth, it is determined when your parents chromosones connected ( eww right lol ) but its a fact.
So before you head on line and try to get the latest thickening product, whilst some will have a temporary effect and can add volume and fullness it is temporary. Your family may be as crazy as a flock of seagulls, if their hair is thick or thin curly or straight chances are yours will be a mix of it and that will make you, you! There are things to manage what you have better, be it products or getting the right cut however you can not change genetics.