Research has shown that altering the macronutrient ratios in calorie restricted diets has an effect on satiety and on ad libitum energy intake. For example, increasing the protein content of a diet from 15 to 30 % has been shown to reduce ad libitum energy intakes. Ketogenic diets are high fat and high protein diets that attempt to limit all carbohydrates. The absence of carbohydrates causes the body to produce ketone bodies in a process called ketosis. It is suspected that this metabolic change is the reason for the success of the diet because during ketosis the desire to eat is reduced. Ketogenic diets have become popular recently, mainly because of the success of the Atkins Diet book, and both anecdotal and research based evidence suggest they are effective in weight loss, particularly for obese subjects.
Research published in the American Journal of Clinical Nutrition in 20081, investigated the effects of a ketogenic diet. In particular, the researchers were interested in comparing the hunger, weight loss and appetite of subjects who consumed either a ketogenic (high protein, low carbohydrate) diet with a non-ketogenic (medium carbohydrate, high protein) diet. Subjects comprised of 17 obese men that consumed either the low carbohydrate (4 %) ketogenic diet or the medium carbohydrate (35 %) diet for 4 weeks. Both diets supplied 30 % protein. Ad libitum energy intakes were lower in the ketogenic diet group compared to the non-ketogenic diet group, and this was reflected in greater weight loss (6.34 kg versus 4.35 kg in the ketogenic and non-ketogenic groups, respectively). Individuals in the ketogenic diet group also reported less hunger.
These results support previous findings that suggest a ketogenic diet is an effective weight loss strategy. The benefit of ketogenic diets may be derived from their ability to cause a reduction in hunger which results in the individual reducing the amount of calories they consume. Rodent studies suggest that 3-hydroxybutyrate might act as a satiety signal. The brain normally uses glucose as a fuel (> 97%), but in the absence of glucose, ketone bodies can provide 30 to 50 % of the brain’s energy needs, which may affect the desire to eat. Acetoacetate concentrations in the urine showed that the ketogenic group were in ketosis after 1 to 3 days, and remained so for the duration of the study. plasma and urine 3-hydroxybutyrate concentrations remained stable from the end of week 1 to the end of week 4.
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