The underlying premise for advocating eating low-glycemic-index foods is that
high-glycemic-index foods cause a rapid elevation in blood sugar that the body
attempts to balance by producing a large amount of insulin. Advocates claim
that human physiology is not designed to tolerate these rapid and prolonged
elevations in blood sugar and insulin caused by the prevalence of modern, high-glycemic-index
foods in the diet. As human civilization has evolved, primitive stone-age diets that
featured naturally occurring, low-carbohydrate foods have been replaced, first
by unprocessed but higher-carbohydrate agricultural foods such as whole grains
and legumes, and more recently by highly processed, low-fiber flours and other
starchy foods, plus an increasing amount of sweets. This trend towards higher-glycemic-index
foods in the diet is therefore deemed unnatural and hazardous to the healthy functioning
of the body.
Research suggests that repeated overproduction of insulin could lead to
insulin resistance, in which cells that normally respond to insulin become
less sensitive to its effects. Excessive high-glycemic-index foods, high insulin levels,
and insulin resistance have been associated with many health concerns,
including obesity, type 2
diabetes, heart disease, and some cancers. Changing
to a low-glycemic-index diet has been shown in most studies to reduce insulin
resistance, help control appetite, improve weight loss results, enhance blood
sugar control in diabetics, lower blood levels of total and LDL
("bad") cholesterol, and raise blood levels of HDL
("good") cholesterol.