Chapter 20 - Nutrition and the circadian timing system
Introduction
Ever since evolution started, life on earth is subject to the daily rhythm of light and dark. As a consequence, many organisms experience a daily rhythm in food availability. Most creatures, ranging from bacteria to humans, developed a circadian timing system to prepare for the alternating daily periods of food intake and fasting. Recent scientific work has generated a lot of knowledge about the circadian control of digestion and metabolism. There are several indications that disturbances in daily rhythms may lead to obesity and diabetes. Consequently, at present, scientists aim to use the increasing knowledge about the interaction between daily food intake rhythms and the circadian timing system to improve health.
Section snippets
Central clock
In mammals, including humans, the central biological clock resides in the bilateral hypothalamic suprachiasmatic nucleus (SCN). The SCN generates an autonomic rhythm of electrical activity with a period of approximately 24 h. This rhythm continues to oscillate even when SCN cells are removed from a living organism and brought into culture (Bos and Mirmiran, 1990, Green and Gillette, 1982, Groos and Hendriks, 1982, Welsh et al., 1995). The SCN is located superior to the optic chiasm and receives
Food intake
During the day, most people grow hungry at regular intervals. At night, however, most people sleep without the arousing effect of appetite despite the much longer period of fasting. Does the SCN modulate appetite and/or the timing of food intake?
Since the discovery of leptin, knowledge about the hypothalamic control of food intake has grown exponentially, and the key role of the hypothalamic arcuate nucleus has been revealed by numerous animal experiments. First, the arcuate nucleus contains
Meal patterns and human health
The circadian control of digestion and metabolism may have important implications for the concept of healthy food intake in humans. Next, we review the literature on the effects of meal timing, meal frequency, and breakfast consumption on human health. Furthermore, we discuss potential implications of the circadian timing system for the timing of enteral tube feeding and parenteral nutrition.
Disturbed rhythms and type 2 diabetes
Type 2 diabetes is considered a multifactorial disease caused by genetic factors and obesity due to excess caloric intake and reduced physical activity. However, several lines of evidence suggest a role of the circadian system in the pathophysiology of type 2 diabetes. We previously discussed how disturbed day–night rhythms can lead to obesity and type 2 diabetes. Interestingly, a number of alterations in the 24-h rhythms of patients with type 2 diabetes have been observed.
First, the daily
Conclusion
In order to adjust to the daily light–dark rhythm, humans possess a central brain clock in the SCN. Furthermore, virtually all cells in the body contain molecular clocks. These peripheral clocks are synchronized both by the SCN and through metabolic signals. Daily rhythms are present in appetite regulation, digestion and absorption, and carbohydrate and lipid metabolism. Thus, meal patterns may strongly influence human health. Strong clues indicate that it is better to maintain a rhythm of
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