Obese Women Convert Carbohydrate to Fat Faster Than Lean Women

De novo lipogenesis is the metabolic route by which mammals convert excessive dietary carbohydrates into fat. Given the prevalence of highly refined carbohydrates in the American diet, this process may play a significant role in the increase in obesity in the U.S. population. Publishing in the American Journal of Clinical Nutrition, McDevitt et al. investigated de novo lipogenesis in lean and obese women in response to both an energy balanced diet (control) and to energy excess due to overfeeding of carbohydrates. They found significant differences in de novo lipogenesis between lean and obese women in response to the control diet, but not to overfeeding of carbohydrates.

Volunteers for the study were 8 lean and 5 obese women, averaging about 52 years of age. In a crossover study design, the women spent a total of 4.5 days each in a whole body calorimeter, which provides accurate measurements of energy expenditure in response to diet. The test diets were carbohydrate enriched with either sucrose or glucose, providing enough energy to maintain energy balance (control) or to provide energy at 50% in excess of daily energy requirements. In lean subjects, overfeeding of both sucrose and glucose produced a 2- to 3-fold increase in de novo lipogenesis; whereas in obese subjects a doubling of the rate of lipogenesis occurred only with sucrose, and no change was observed with glucose.

With the control diet, de novo lipogenesis was nearly twice the rate in the obese than in the lean subjects, regardless of the source of the carbohydrate. The type of carbohydrate overfeeding (sucrose or glucose) showed no difference in effect on de novo lipogenesis. Women who had a high rate of de novo lipogenesis in response to the carbohydrate-rich control diet consistently had a high rate of response to the overfeeding diet. This result suggests that some individuals may have an intrinsically higher, perhaps genetic, potential for de novo lipogenesis.

Although rates of de novo lipogenesis in the carbohydrate-enriched energy-balanced control diet were significantly greater in the obese than in the lean women, the absolute quantities of fat synthesized from carbohydrate via de novo lipogenesis during both phases of the study were relatively small. An editorial by Hellerstein points out that de novo lipogenesis is a path of last resort in the bodys overall carbohydrate metabolism. Future research should focus on the human macronutrient energy economy, in which dietary fats and carbohydrates have separate, but equally important, metabolic pathways for the conversion of surplus energy to fat stores.

  • McDevitt, Regina M et al. De novo lipogenesis during controlled overfeeding with sucrose or glucose in lean and obese women. Am J Clin Nutr 2001;74:737-46.
  • Hellerstein, Marc K. No common energy currency: de novo lipogenesis as the road less traveled. Am J Clin Nutr 2001;74:707-8.

Source: American Journal of Clinical Nutrition

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