High fat diets upset our biological clock | health

Researchers from the Hebrew University of Jerusalem have shown that diets which are high in fatty foods can affect the balance of our circadian rhythms - the regular changes that occur in our bodies during a 24-hour day.

The biological clock regulates the expression and activity of enzymes and hormones involved in metabolism, and disturbance of the clock can lead to problems such as hormone imbalance, obesity, psychological and sleep disorders and cancer.

While light is recognized as the strongest factor affecting the circadian clock, in their experiments with laboratory mice, Dr. Oren Froy and colleagues at the university's Institute of Biochemistry, Food Science and Nutrition, in the Faculty of Agriculture, Food and Environment in Rehovot, showed that there is a cause-and-effect relation between diet and biological clock imbalance.

To examine this theory, Froy and his colleagues, Ph.D. student Maayan Barnea and Zecharia Madar, the Karl Bach professor of Agricultural Biochemistry, tested whether the clock controls the adiponectin signaling pathway in the liver and, if so, how fasting and a high-fat diet affect this control.

It's not just the calories that count

Adiponectin is secreted from differentiated adipocytes (fat tissue) and is involved in glucose and lipid metabolism. It increases fatty acid oxidation and promotes insulin sensitivity, two highly important factors in maintaining proper metabolism.

The researchers fed mice either a low-fat or a high-fat diet. They followed this with a fasting day, and then measured components of the adiponectin metabolic pathway at various levels of activity.

In mice on the low-fat diet, the adiponectin signaling pathway components exhibited normal circadian rhythms. Fasting resulted in a phase advance. The high-fat diet resulted in a phase delay. Fasting raised and the high-fat diet reduced adenosine monophosphate-activated protein kinase (AMPK) levels. This protein is involved in fatty acid metabolism, which could be disrupted by the lower levels.

In an article soon to be published by the journal Endocrinology, the researchers suggest that this high-fat diet could contribute to obesity, not only through its high caloric content, but also by disrupting the phases and daily rhythm of clock genes.

They contend also that high fat-induced changes in the clock and the adiponectin signaling pathway may help explain the disruption of other clock-controlled systems associated with metabolic disorders, such as blood pressure levels and the sleep/wake cycle.