What is metabolism? Long explanation short, metabolism is the process in one's body where food (calories) are converted into energy (by your muscles).
Therefore, why is it important to have a fast metabolism? Well, the more calories your body uses, the less calories are stored - which creates fat - and therefore, the more you lose weight because your body also uses stored calories (stored fat) as energy.
Here are six ways to naturally boost your metabolism:
Workout consistently. The more powerful your muscles are, the more calories they'll burn during workouts and while resting. That's very important and goes hand-in-hand with the definition of metabolism.
Drink healthy sources of caffeine. The most healthiest are black coffee and green tea. Both without anything added. I understand that black coffee is an acquired taste, but once you do acquire a taste for it, it'll be your favorite thing to drink! Both black coffee and green tea have antioxidants, so therefore there's bonus to the health benefits they provide. Coffee has a bad rep because of the crap people add to it, so don't get caught up in that.
Water! Water, water, water! Drink water all day. Most of our bodies are made up of water, and you lose water with everything you do: breathing, bathroom trips, sweating, etc. Water is responsible for carrying nutrients across your blood stream to the right places, and promotes healthy muscles.
Natural fat burning supplements. Usually it's hard to find good ones, but once you do find good ones, you're hooked (and not because you have withdrawal symptoms when you stop - you don't - but rather because they not only work but also have health benefits due to the natural/healthy ingredients). Supplements are there to supplement your diet, so don't expect them to work while you eat garbage and do no exercise.
The right diet. This one is tricky, because not every diet is for everyone. For example, carb-cycling is my favorite type of metabolism-boosting diet, because the process involves eating a controlled amount of low carb (and low fat) foods, while consuming a lot of protein, and once or twice a week, you have a cheat day (which is where the cycle happens: you eat carbs - and fat if you also cut that - which therefore, creates your metabolism to suck all those carbs in as it develops a memory to use your stored fat as energy. No matter what, always avoid processed foods, eat a lot of protein and vegetables, and I also love spicy food! Spicy foods (jalapenos, garlic, etc) have been proven over and over again to boost people's metabolism.
Sleeping. Studies have shown that if you don't get enough sleep, your metabolism's ability drops significantly, while also leaving you with cravings for sugary foods and binge eating, which doubles your weight gaining problem. Therefore, I recommend you getting 7-9 hours of sleep (and, by the way, the more, the better! There is no such thing as too much sleep).