TYPE 2 DIABETES & OBESITY

Before birth insulin commands the baby’s growth. It ensures that the speed of growth matches the availability of food. People develop the common form of diabetes, which begins in adulthood, for two reasons: either their bodies do not make enough insulin, or their tissues do not respond to it. Insulin is made by the pancreas in cells called beta cells. These beta cells develop before birth. In animals whose mothers were under-nourished the beta cells do not function properly. They are less able to make insulin and meet the challenges of managing the body’s sugar. One of these challenges is obesity, which makes the body less responsive to insulin, so that more of it is required. A reduced ability to make insulin, combined with an excess requirement for it, makes it impossible to maintain the amount of sugar in the blood at normal levels. The levels rise; diabetes develops.

Sensitivity to insulin is established in the womb.Obesity is not the only cause of loss of responsiveness, so-called “resistance”, to insulin. Sensitivity to insulin is established in the womb. At any body weight people who were small at birth are more resistant than those who were large. It seems to be the thin, low birthweight baby that is most prone to becoming insulin resistant later. Like thin children, thin babies lack muscle though they may also lack fat. If you run your fingers down the thigh of a thin newborn baby you will readily feel the bone because the muscle is sparse. Muscle seems to have a low priority in the womb, and its growth is readily sacrificed if a baby is undernourished.

In the short-term resistance to insulin could be beneficial. If the muscles of an undernourished baby become resistant to insulin, more sugar will remain in the blood. This sugar will be available to the brain whose growth is thereby protected. Insulin resistance could be part of a system that enables the baby to be thrifty in its use of sugar. Priority is given to maintaining sufficient sugar in the blood rather than storing it in the muscles. Thrifty handling of sugar becomes ‘hard-wired’ and persists through life. It becomes a liability when food becomes more freely available after birth. The blood becomes flooded with sugar, and obesity makes the body still more resistant to insulin. Diabetes develops.

Between birth and one year babies get fatter and their body mass indices, weight/height², rise sharply. After that age, as the child grows taller, but does not continue to require large fat stores, the body mass index falls. At around six years of age the body mass index begins to rise again, the so called 'adiposity rebound'. The timing of this rebound is critically important to the later development of obesity and diabetes. Adiposity rebound at an early age is a strong predictor of both disorders in adult life. For reasons that we do not understand low weight gain during infancy, leading to thinness at two years, triggers an early adiposity rebound. The thin two year old is therefore at the greatest risk of diabetes in later life.