Carbohydrates constitute a major fraction of energy yielding macronutrients (along with fats and proteins).
Nutritionists recommend 45-55% of total energy intake should be from carbohydrates to maintain healthy balanced diet .
Carbohydrates are broadly classified into simple and complex carbohydrates depending upon the number of basic sugar units.
Mono and Disaccharides (1 or 2 sugar units) encompass simple sugars such as glucose (white bread, white rice), fructose (fruit juices), sucrose (table sugar, sugar sweetened beverages like cola), whereas oligo (3-10 sugar units) and polysaccharides (>10 sugar units) make up complex carbs including but not limited to starch and dietary fiber found in whole grains, fruits, legumes and vegetables.
Most foods are composed of simple and complex carbs in variable amounts.
Generally, simple sugars are easily digested and metabolized, have rapid blood glucose raising potential, higher energy density and their chronic excess consumption increases the risk of diabetes substantially.
Conversely, complex carbohydrates may or may not be metabolized easily which depends on the solid/liquid state, processed or not, glycemic index (i.e. glucose raising potential of a particular food compared to white bread/glucose) and molecular conformation (amylose to amylopectin ratio).
Solid, nonprocessed, low glycemic index carbohydrates with high amylose to amylopectin content like resistant starch and dietary fibre (intrinsic plant cell wall non-starchy polysaccharide) are found to decrease the longterm diabetes and cardiovascular mortality risk in multiple studies.
In a nutshell, limiting simple sugar intake (like sugar sweetened beverages) and increasing consumption of dietary fiber (like whole grains, legumes) is advised for maintaining healthy diet pattern