Energy Intake
There is now a considerable amount of evidence to suggest that rapid acculturation is associated with increased rates of type 2 diabetes (11). Several characteristics of the Western lifestyle predispose to overnutrition and obesity, which in turn increases the risk of developing insulin resistance and type 2 diabetes - particularly in individuals or populations with a genetic predisposition for diabetes. Physical inactivity and high intakes of energy-dense foods lead to an energy intake in excess of requirements (2,12).

An impressive decline in diabetes death rates in several places was reported during World Wars I and II in locations affected by food shortages.

The contribution of overnutrition to risk of diabetes has also been demonstrated.  When food consumption per capita rose sharply in Japan,  Taiwan,  and some Pacific islands,  there was also a sharp rise in the prevalence of type 2 diabetes (11).

A number of studies have demonstrated improvements in metabolic parameters among people with impaired glucose tolerance (IGT) after interventions aimed at reducing energy intake and increasing physical activity,  suggesting that it may be possible to reduce the incidence of type 2 diabetes (13 - 15).  Indeed,  some recent intervention studies have demonstrated the potential for weight loss to reduce the risk of progression from IGT to type 2 diabetes. The Finnish Diabetes Prevention study included 522 overweight persons with IGT, randomized to a control group or to intensive lifestyle intervention.

The cumulative incidence of type 2 diabetes after 4 years was 11% in the intervention group and 23% in the control group. The risk of type 2 diabetes was reduced by 58%, and this outcome was directly related to changes in lifestyle (17,18).

The Diabetes Prevention Program in the United States included 3234 persons of diverse ethnic background with IGT (19).
Participants in the intensive lifestyle program reduced their risk of developing type 2 diabetes by 58% over 3 years of follow-up, and the risk reduction was 71% among persons over the age of 60 years. Of interest is the finding that metformin, the pharmacological agent tested in this study, resulted in a risk reduction of 31%, which was less than the risk reduction observed for lifestyle intervention (20).

Excess body fat is perhaps the most important modifiable risk factor for the development of type 2 diabetes (11,15). It is estimated that the risk of type 2 diabetes attributable to obesity is as great as 75%.

However, it is important to emphasize that in most intervention studies aimed at weight reduction there are major difficulties in disentangling the potential benefits of weight loss from the effects of altering intakes of individual foods and nutrients and increasing physical activity, all of which have the potential to reduce diabetes risk.

Energy intake is difficult to assess adequately in large-scale epidemiological studies,  even when the best available instruments are employed, and it has been demonstrated that overweight or obese persons underestimate their energy intake. Nevertheless, the consistency of beneficial effects shown in intervention studies in which body weight was reduced strengthens the recommendation: energy intake in excess of requirement and overweight should be avoided, particularly among those with a familial predisposition. In addition, the Finnish Diabetes Prevention study recently could show beneficial effects of high fiber, low-fat diets in the prediction of long-term weight loss as well as in the risk reduction of type 2 diabetes (18). Such advice probably offers the best hope of reducing the risk of developing resistance to the action of insulin and progression to type 2 diabetes (8,14,21).