Lene Secher Myrmel:
The dietary composition and source of macronutrients determine obesity development

Date: 15-09-2014    Supervisor: Karsten Kristiansen & Lise Madsen

The drastic worldwide increase in obesity during the last decades is accompanied with several different health disorders. The underlying mechanisms for this escalation is not clear, but certain alterations in the dietary macronutrient composition are suggested to be of importance. In addition to an elevation in energy intake, these alterations include increased consumption of refined carbohydrates and a relative decrease in protein consumption. The relative intake of dietary fat has not increased during the last decades, but the proportion of vegetable oils has increased at the expense of saturated fat and marine oils.

To further investigate the importance of the macronutrient composition on obesity development, we have performed a series of mice experiments. Our results demonstrate that both the amount and source of macronutrients influence obesity development and related disorders. The anti-obesity and insulin-sensitizing effect of marine n-3 polyunsaturated fatty acids (PUFAs) are well described in rodents. In line with this, we show that replacing marine oil with soybean oil in salmon feed, translates into a lower content of n-3 PUFAs in salmon fillets leading to aggravated insulin resistance in mice fed salmon in a Western diet. However, a high dietary content of sucrose or other high glycemic index carbohydrates attenuate the anti-obesogenic effect of n-3 PUFAs. When casein is used as the protein source, a high protein:carbohydrate ratio prevents high fat diet induced obesity, this is observed in studies where the dietary fat is enriched with either marine n-3 PUFAs or vegetable n-6 PUFAs. The protein:carbohydrate ratio furthermore influence on the accumulation of POPs in adipose tissue. However, we also demonstrate that the protein source determines the potential of high protein diets to attenuate obesity development. The gut microbiota is less affected by alterations in protein:carbohydrate ratio and adiposity, but is altered in response to an elevated fat intake.

The macronutrient composition is able to affect obesity development through direct influence on energy consuming metabolic processes, such as gluconeogenesis, amino acid degradation, urea synthesis and nonshivering thermogenesis.