Carbs are the starches, fibres, and sugars found in foods such as fruits, vegetables, milk products, table sugar, and grains. When you eat them, the saliva enzymes in your mouth turn the molecules into smaller sugar units, such as glucose and fructose. Your digestive system then processes these smaller units, after which they reach your bloodstream as glucose. Then, bodily tissues such as your heart, muscles, and brain can use these glucose molecules for fuel.

The above is, in a nutshell, how your body converts and uses carbs. However, it is essential to note that not all carbs are created equal. Those from grain, for instance, have a different effect on your body than carbs from vegetables. 

While there are many carb variations, we can broadly label them as either slow-acting or fast-acting. 

Fast-acting carbs are converted into glucose and released into your bloodstream quickly. Examples are the carbs found in bread and cakes. Slow-acting carbs are released into your bloodstream at a leisurely pace, so to speak. Examples are the carbs contained in leafy green vegetables and some fruits like berries.

Your carb intake on the keto diet should comprise of the slow-acting carbs, that also have a low carb content, as they have less of an impact on your blood sugar level and therefore do not spike insulin. That is better for your health and supports fat loss. In fact, elevated insulin levels make it impossible to lose fat or get into ketosis