I always wondered why some skinny people don’t gain weight even if they eat a lot. And then there is the opposite. Overweight people will gain weight even on days that they don’t eat a lot.
I suppose that it has something to do with the eating habit and the size of the intestines. People who consistently eat more tend to have a larger intestine with more nutrient absorption capacity. I looked around the internet to see if a study supports that.
As early as 2011, it has been shown in fruit flies that the intestinal stem cells secrete insulin that promotes cell growth.
The article, Intestinal stem cells respond to food by supersizing the gut describes that in times of increased food intake, insulin secretion increases, and more cells are produced, leading to a larger intestinal tract.
The reverse also happens. In times of less food, the intestines decrease in size, which is consistent with autophagy.
Autophagy is when the body breaks down and recycles redundant, dysfunctional, and precancerous cells.
Since then, many studies have been done on fruit flies and their gut. These fly studies may apply to humans because the factors and pathways are similar.
One research shows the balance between cell addition and cell loss. The study by Liang et al. showed that healthy intestinal cells or enterocytes block the multiplication of intestinal stem cells that become adult cells.[1]
In comparison, the death of old cells releases a block on stem cell divisions.[1]
Interestingly, the effect of the cells dying of natural causes is only on nearby stem cells. This prevents an unwanted increase in the size of the whole intestine.
However, the effect on the injured cell is more widespread if trauma happens. In an email to Stanford Scope, Lucy O’Brien, one of the authors, said,
When cells are killed by trauma, they actually emit different signals compared to when cells die a natural death. As others have shown, these trauma-induced signals alert the stem cells that there’s an emergency, and they set off a chain of events that propagates across a wide swath of tissue, recruiting even uninjured cells to help repair the damage.
By contrast we found that when cells die a natural death, the signals they emit — certain types of epidermal growth factors EGFs — operate only within close range of the dying cell. It’s like a whisper instead of a siren.
There is more to the intestines than nutrient absorption.
Don’t Get Sick!
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- Liang J, Balachandra S, Ngo S, O’Brien LE. Feedback regulation of steady-state epithelial turnover and organ size. Nature. 2017 Aug 31;548(7669):588-591. doi: 10.1038/nature23678. Epub 2017 Aug 23. PMID: 28847000; PMCID: PMC5742542.
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