High fat diets can destroy the body clock
Do you like a snack at bedtime? We certainly do, and so do rats, at least ones allowed to feast on a high fat diet. And now, new research has shown that rats fed on a high fat diet end up with broken body clocks and disrupted eating and sleeping patterns. Cells in the brainstem that would normally make you hungry in the day and not-hungry at night appear to be disturbed by the high fat diet. There are implications for how we might treat human obesity in the future. Eva Higginbotham spoke to lead author Lucasz Chrobok to find out more...
Lucasz - In this new study, we found that in rats fed a high-fat diet, the activity of this brainstem clock is actually severely disturbed. And at the same time, these high fat diet fed rats increased their food intake during the day, the time these nocturnal rodents should normally spend on sleep and rest rather than feeding
Eva - You basically fed some rats a healthy diet, some rats a high fat diet, and saw that their sleeping behaviour changed?
Lucasz - We did not really measure the sleep behaviour, but we measured the food intake around 24 hours. What we saw in this well-balanced healthy group; that their food intake was limited to their active phase. With the high-fat diet fed rats; their food intake was all over the place. They would eat during the active phase but they would also eat during their behaviourally quiet time, which is day for these nocturnal rodents.
Eva - How high fat is high fat for a rat?
Lucasz - The standard high diet is 70% calories from fat. It's a really high fat diet.
Eva - Have you tasted it? What does it taste like?
Lucasz - I haven't tasted it, but it smells amazing, like cookies.
Eva - Amazing. When you looked at the actual nerve cells of the brain that are involved in setting the circadian rhythm, did you see that they were behaving differently?
Lucasz - Yes. Normally under a standard well-balanced diet, the neural activity of the brainstem clock is very rhythmic. During the day the activity goes up, it peaks at the late day. Then the activity slowly goes down during the night. And in the high-fat diet the neuronal activity of this brainstem clock is nearly totally flat. It does not really distinguish the time of the day.
Eva - That's really amazing. Do you think then that there's something about the fat in the diet that was affecting the clock? Or do you think it was something more about the rat's behaviour because they love the high-fat food so much?
Lucasz - We don't know the answer to this question because it either can be the calorie content of the diet itself, the fat that actually affects the brain cells, but it also may be a behaviour that as a feedback affects the brain. Because of the high tastiness of the food, rats eat it all the time. Then because the feeding pattern actually affects the clock, it just destroys it.
Eva - Rats are nocturnal aren't they? How applicable do you think their circadian rhythm and food intake system is to humans when we're obviously supposed to be up during the day and asleep at night?
Lucasz - Yes. One must be really cautious to extrapolate results from rodents to humans. However, with the brainstem being so evolutionary ancient, we really hope that this basic clock mechanism may be conserved among species
Eva - Do you think any of this could be linked to shift workers? People who are working during the night and then sleeping during the day?
Lucasz - Definitely. I think it's relevant to shift work in general. We know that in shift workers there is a high increase of obesity, some kind of cancer and cardiovascular disease. It is actually now speculated that it is good to lock your feeding patterns to the light dark cycle rather than to your activity cycles. If you are a shift worker and you actually work during the night, it would be good for you to even wake up during the day, which is a time you should eat, and eat during the day.