Transfats, diabetes and obesity

Diabetes and obesity are major health problems for large numbers of people in welathy countries, and increasingly in poorer countries of the world too, where their advance has taken place alongside the introduction of 'western' diets and eating patterns. Overconsumption of sugar and refined carbohydrates are clearly implicated in this. But could trans fats also be involved?

Evidence is growing that this is indeed the case. The likely mechanism is that the assimilation of trans fats into cell membranes impairs their function, for example reducing cellular response to hormones such as insulin. The following scientific publications indicate a clear link between trans fats and type 2 diabetes:

• Salmeron et al (Harvard University, 2001) investigated the relationship between fat consumption and type 2 diabetes, following 84,204 women aged 34-59, none of whom had diabetes, cardiovascular disease, or cancer when the study began in 1980. Over the next 14 years, 2,507 of them developed type 2 diabetes. No significant correlation was found between the incidence of type 2 diabetes and the intake of total fat, saturated fat or monounsaturated fat. However a 5 percent increase in dietary polyunsaturated fat caused a 37 percent risk reduction; and a 2% increase in trans fat led to a a 39 percent increase in risk. Replacing trans fat in the diet with polyunsaturated fat would therefore cause substantial reductions in the development of type 2 diabetes.
  [Salmeron J, Hu FB, Manson JE, Stampfer MJ, Colditz GA, Rimm EB, Willett WC (2001) "Dietary fat intake and risk of type 2 diabetes in women". American Journal of Clinical Nutrition 73 (6):1019-26.]
• Barnard et al (University of Maryland, 1990) found that trans fats adversely affected insulin receptors and insulin binding.
  [D.E. Barnard, J. Sampugna, E. Berlin, S.J. Bhathena and J.J. Knapka (1990) "Dietary Trans Fatty Acids Modulate Erythrocyte Membrane Fatty Acyl Composition and Insulin Binding in Monkeys". Journal of Nutritional Biochemistry 1:190-195.]
• Kuller (University of Pittsburg, 1993) found that regular consumers of margarine made with partially hydrogenated vegetable oil had raised insulin levels in response to glucose load.
  [Kuller (1993) "Trans Fatty Acids and Dieting" (Letter) The Lancet 341:1093-1094.]
• The National Obesity and Weight Control Symposium (New York, April 1993) heard that comsuming trans fatty acids affected the cell membranes of muscle tissue in a way that could lead to diabetes, the effect being exacerbated by obesity.
• Mann (1994) argued that insulin resistance would develop in response to eating trans fats.
  [B.V. Mann (1994) "Metabolic Consequences of Dietary Trans Fatty Acids", The Lancet 343:1268-1271.]
• Simopolous (1994) called for clinical investigations to assess the effect of dietary trans fats on insulin resistance.
  [A.P Simopolous (1994) "Is Insulin Resistance Influenced by Dietary Linoleic Acid and Trans Fatty Acids?", Free Radicals in Biology and Medicine 17:367-372.]

Diminished response to insulin, as documented above, can also lead to obesity, since it is harder for the body to convert reserves of fat into usable energy: a need for physical energy is more likely to be met by increased eating, rather than utilisation of energy stored as fat.