Updated: Mar 1, 2019
The definition of detox within the nutrition context is to clear your body of toxins, a "reset" button if you will. Well here is some hard knowledge for you.
The SCIENCE!: Your wonderful body is a result of millions of years of evolution, and trust me, mother nature has figured out a way to keep your insides clean. Introducing to my right, your LIVER. Its job is to filter your blood coming from your digestive tract, back to your body. It metabolizes drugs, cleans out harmful chemicals like ethanol (alcohol), metabolizes fats, proteins, and carbohydrates. Your liver also secretes bile, which helps your body absorb fats & fat soluble substances like vitamin K, A, D, E. However Bile also is used to usher blood related toxins out of your body via your feces.
Introducing YOUR KIDNEYS! their function is to also filter your blood, cleansing it from waste and regulate your electrolyte levels as well as the delicate balance of salt, water, and minerals.
Why juice or tea cleanse don't work and sometimes are dangerous! A juice cleanse consist of blending ton of fruits into a blender and making this your only source of "food". By doing so you not only deprived your body of much needed fiber (blender destroys them all) but you also just ingesting sugar! If you are a diabetic, that can be lethal as the sugar could spike your glucose levels. Teas marketed as cleanses contain senna, which is a laxative, that can prevent your body from properly absorbing the nutrients it needs and also affects the function of your liver, adding unnecessary stress on your cleansing organs.
Conclusion: Your body is an extraordinary machine capable of amazing things like keeping everything in check so you may survive and thrive! all you need to do is support it, how? getting enough sleep, getting enough exercise, EATING! appropriately with right portions and right types of food. Everything else is already on autopilot.