Katsutaka Oishi (Leader) of the Clock Cell Biology Research Group, Institute for Biological Resources and Functions (Director: Masanao Oda), National Institute of Advanced Industrial Science and Technology (AIST) (President: Tamotsu Nomakuchi) and Shuichi Horie (Professor) and others of Kagawa Nutrition University have found that the circadian clock can be controlled by feeding a low-carbohydrate diet in mice.

A low-carbohydrate, ketogenic diet was administered to mice for 14 days and subsequently, the expression of a clock gene which is a marker of the biological clock was analyzed. The clock gene was expressed 4 to 8 hours earlier in the mice on low-carbohydrate diet than in the control mice.

Since mouse is a nocturnal rodent and its circadian activity is strongly suppressed by light, it is difficult to observe the endogenous circadian clock of mice in an environmental light-dark (day-night) cycle. Hence, the mice were transferred into constant darkness and the effects of the diet on their behavioral patterns were recorded. The mice on the low-carbohydrate diet woke up earlier (i.e., it became an early riser) than the control mice.

The forward shift of activities was also observed in mice with DSPS (delayed sleep-phase syndrome; mice with DSPS tend to oversleep), that were fed a low-carbohydrate diet. We anticipate that this low-carbohydrate ketogenic dietary treatment would be a new therapy for sleep disorders or jet lag.

The results of this study will be published in an American scientific journal, "Arteriosclerosis, Thrombosis, and Vascular Biology."

Figure 1. Early expression of a clock gene after administration of ketogenic diet

Figure 2. Forward shift in the wake-up time of the mice

Sleep disorders increased in a "24-hour Society" have become a serious social problem today. A circadian clock which is comprised of clock genes is involved in the circadian rhythm sleep disorders, although the detailed mechanisms are still unclear. Sleep disorders are usually treated by several treatments such as appropriately-timed exposure to bright light, or vitamin B₁₂ or melatonin administration, although the effects of these treatments vary among individuals. In addition, the reaction mechanisms of these treatments have not yet been elucidated in detail. Therefore, the development of a new treatment for sleep disorders having different mechanism from those of conventional treatment is desired.

AIST is investigating the mechanisms of biological clocks and their relation to sleep disorders. The findings of our study indicate that fibrate, which acts on the nuclear receptor PPARα and reduces the lipid levels, alleviates the symptoms of circadian rhythm sleep disorders of mice (AIST press release of April 25, 2007).

AIST and Kagawa Nutrition University are also collaborating on study in the relationship between circadian clocks and nutrition with an aim to improve sleep disorders by using dietetic therapies.

Circadian rhythms are regulated by the circadian clocks that are comprised of clock genes. In mammals, including humans, various clock genes are expressed in a circadian manner not only in the brain but also in almost all organs such as the heart, liver, and kidney. In this study, mice fed with a low-carbohydrate diet showed early expression of a clock gene, resulting in the forward shift of the circadian clocks.

The normal diet of mouse includes about 50% of carbohydrates. In our study, a ketogenic diet containing only 0.73% carbohydrate was prepared and fed to mice for 14 days, and the expression of the clock gene (period2) was determined. This gene was expressed 4–8 hours earlier in the mice that were on the ketogenic diet than in the control mice (Figure 1).

Since mouse is a nocturnal rodent, its diurnal activity is strongly dominated by light; hence, the behavioral patterns of the mouse did not change under light-dark (day-night) conditions. In order to observe the endogenous circadian clock, we transferred the mice into continuous darkness. The behavioral patterns of mice fed with a low-carbohydrate diet displayed a forward shift, i.e., they woke up earlier than the control mice (Figure 2).

The period of the circadian clock (cf. approximately 25 hours in humans) was calculated from the slope of the red line shown in Fig.2. The red lines correspond to the wake-up times of the mice. The circadian period of the mice on ketogenic diet was 15–20 minutes shorter than that of the control mice.

Further, administration of the low-carbohydrate diet also caused the early rising effect in model mice of DSPS, i.e. Clock gene-mutated mice, which tend to oversleep.

A low-carbohydrate diet can be expected to serve as one of the new therapies for a wide variety of sleep disorders or jet lag.

In future, we aim to elucidate the molecular mechanism of changes in the circadian rhythms of mice fed with a low-carbohydrate diet.

At present, ketogenic diets are used in the treatment of epilepsy and obesity. However, the use of this diet has raised concerns in the medical and nutritional fields and a general consensus regarding the safety of this therapy is awaited. Therefore, it is important to verify the long-term safety of this dietary treatment, especially before it is applied in the treatment of human diseases.