Glycemic carbohydrates, of which starch is the most important, are the main source of glucose for human energy metabolism. Current guidelines indicate that a standard ‘healthy diet’ should be based on around 50% of energy from carbohydrates. While it is possible to survive for some time with low levels of starchy plant food, a habitual low starch diet limits physical performance and compromises reproductive capacity.
Major carbohydrate sources in plants include underground storage organs (USO) (roots, tubers, rhizomes) and above ground storage organs (ASO) (stems, seeds, nuts). Indirect evidence for cooking, in the form of hearths and evidence for fire, extends deep into the Lower Palaeolithic. Carbonised fragments of edible plant storage organs some with possible evidence for grinding, and grinding tools with evidence for processing starchy plants, have been recovered from some later Palaeolithic sites. Processing, including cooking and grinding, provides a more efficient mechanism to obtain energy and makes these an efficient source of preformed glucose, but it also increases their glycemic index (GI). This can lead to fat deposition particularly when associated with low physical activity.