Authors

Manson, Willett, Stampfer, Colditz, Hunter, Hankinson, Hennekens, & Speizer (1995)¹⁹

Conclusion

Literature review shows high BMI is associated with increased incidence of type 2 diabetes

Concern

Caution is needed when inferring causality from statistical studies demonstrating that two variables are associated.

Authors

Pi-Sunyer (1996)²⁰, Porth (1994)²¹, & Reaven (1988)²²

Conclusion

*Insulin resistance is the primary pathophysiology for type 2 diabetes.
*Many studies have suggested a causal relationship between increased BMI and increased insulin resistance.
*Research evidence supports a relationship between increased BMI, insulin resistance & type 2 diabetes.
*The prevalence of concurrent high BMI, insulin resistance, & Type 2 diabetes in study populations seems confirmatory of a causal relationship.

Concern

Do other factors such as sedentary lifestyle play a significant role in the causal pathway described above?

Author

Gaesser (1997)²³

Conclusion

*There may be a genetic predisposition for insulin resistance for some people.
*Such a genetic predisposition may be aggravated by participation in sedentary lifestyle coupled with intake of a predominantly high fat diet.
*The presence of such an environmental & genetic combination may lead to development of diseases such as Type 2 diabetes secondary to the presence of insulin resistance.
*The regular intake of fat & lack of physical activity may alter the genetically susceptible body's sensitivity to insulin.
*It may be that the association between increased BMI & insulin resistance is nothing more than innocent co-existence.

Concern

The mere presence of two or more variables in the same individual does not infer an inherent causal relationship.