2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
American scientists from the Department of Neurology have developed an automated feeding system that can work around the clock and record the behavior of laboratory mice, and found that the behavior and health of mice is influenced not so much by the calorie content of the diet, but by the diet and the length of time the animals spend starving. The results are published in the journal Cell Metabolism.
Scientists have long noticed that restricting calorie intake has a positive effect on the lifespan of mammals, including monkeys, but there is currently no definitive explanation for this effect. Longevity is associated with a healthy diet and circadian rhythms. Health and weight can be influenced by the timing and frequency of eating, and in the case of laboratory mice, which, among other things, are awake at night (after hours), it was difficult to offer an adequate - and controlled - diet for them. To shed light on the effect of these indicators, scientists have developed an automatic system that, in addition to regulating the basic parameters of feeding, recorded the daily activity of rodents. The researchers' goal was to understand how important fasting and meal times are compared to calorie restriction.
Over 43 days, scientists tested different feeding regimes, manipulating the time during which food was available (TR-day and TR-night), arranging fasting days (AD), and cutting the diet by 30% of the normal amount of calories consumed (CR) … The daily activity of the experimental animals was constantly monitored: the time of eating, the amount, physical activity on the wheel; their weight, glucose levels, stomach, liver and white adipose tissue (eWAT) size were monitored. The group data were compared with the AL group, in which food was served around the clock and without restriction.
With complete freedom (AL), motor activity and mealtime correlated and occurred mainly at night, with individual differences; the weight of the mice also differed, despite the genetic homogeneity of the individuals and similar appetites. Many individuals regularly ate some of their food during the day, and they had more weight. Mice that had food available during the night (TR-night) showed similar results, while those in which food was available only during daylight hours (TR-day) ate significantly less, but ate large portions. The CR group had the largest portions. Regardless of what time the daily supplies were replenished, the animals pounced on food and ate everything within two hours. It is important to note that the daily intake in the CR group was only slightly lower than in the TR-day group, but this limitation still greatly affected the behavior of the animals. In the group with limited consumption at night, behavioral changes were most noticeable: the rodents remained active during the daytime, taking less time to rest. In the group where fasting days alternated with unrestricted meals, motor activity first increased on fasting days, but then the difference leveled off, and consumption on "days of abundance" corresponded to consumption over 48 hours in the free regimen group.
Behavior of laboratory mice depending on the feeding regime: food intake and motor activity in the wheel. Pink shading represents the time when food is available, and arrows indicate the beginning of food intake
Physical activity during the day and during the day (top), the number of pellets consumed per day (bottom), depending on the feeding regimen. Asterisks indicate statistically significant difference compared to AL (gray bar)
Comparison of indicators of change in weight, glucose levels, food intake for 2, 5 hours, and white adipose tissue mass (eWAT), depending on the feeding regimen. In the fasting mode, the weight of the animals changed depending on the phase (feeding-fasting)
Despite the fact that in the three groups the average daily consumption was significantly lower than in the group without restrictions, weight decreased only in one of them: in the group that ate at night and had a limited diet. The mass of adipose tissue decreased in other groups with a reduced diet, that is, in those animals that ate in the daytime, there was a decrease in adipose tissue mass, but the weight changed insignificantly. The authors assume that fat stores were retained in other tissues. In the group with "fasting days" the weight of the animals fluctuated: it dropped significantly on hunger days, and reached the norm when food appeared. Glucose levels were low in those mice that ate less, regardless of dietary rhythms and physical activity.
Overall, the results suggest that lower calorie intake does not guarantee weight loss, and that physical activity and health parameters are significantly influenced by other conditions associated with circadian rhythms and duration of fasting. However, many of the phenomena that have been discovered have yet to be explained with the help of new research - for example, the activity that arose in one of the groups during the rest hours, which may be explained by the effect of calorie restriction on the suprachiasmatic nucleus of the hypothalamus, the influence of hunger, or reflect the behavior of anticipation of feeding. It is also important to understand how different diets affect health, youth, and longevity in the long term, and the automated system developed by the authors opens up prospects for such research.
Circadian rhythms explain the jet lag effect, they are associated with the regulation of metabolism, and many diseases are believed to arise from their disruption. However, the violation of circadian rhythms sometimes occurs in the wild, so this topic is especially attracting the attention of scientists.