Human evolution: starvation mechanism (Introduction)

by David Turell , Wednesday, January 30, 2019, 18:57 (2124 days ago) @ David Turell

It has been known for many years that a marked fall in calorie intake can drop basal metabolism by as much as 300 calories a day. An insight to that control system is found:

https://medicalxpress.com/news/2019-01-intestinal-immune-cells-key-role.html

"The team's study focused on a protein called integrin β7, which is known to direct immune cells to the gut but not previously to have any influence over metabolism. The MGH team initially found that mice lacking the gene for integrin β7 and fed a normal diet gained equal amounts of weight as did a group of control animals, even though the β7-negative animals ate more food and were equally as active. Metabolic testing indicated that the β7-negative mice converted more food into energy, suggesting they had a higher basal metabolism. They also burned more glucose in brown fat, were more glucose tolerant, had lower triglyceride levels and better fat tolerance than did control mice.

"To investigate whether these benefits persisted under nutritional conditions known to induce the metabolic syndrome—a group of symptoms associated with type 2 diabetes and cardiovascular disease—they fed both β7-negative mice and control mice a diet high in fat, sugar and sodium. The β7-negative mice remained lean, glucose tolerant, and did not develop hypertension or other typical results of a high-fat diet. The control mice did become obese, with elevated blood pressure and reduced glucose tolerance.

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"Experiments with a mouse model genetically programmed to develop elevated cholesterol found that blocking β7 expression in the bone marrow, where immune cells are generated, maintained normal lipid levels in the animals, in spite of their being fed a high-cholesterol diet. Mice with β7-negative marrow excreted more cholesterol, had improved glucose tolerance and were less likely to develop arterial plaques and other cardiovascular risk factors than were animals with normal bone marrow expression of β7.

"A search for the cells responsible for β7's metabolic impact revealed that the protein's expression was highest in a group of T cells present in the lining of the small intestine. While β7 guides several types of immune cells to the intestines, only these β7-expressing intraepithelial T cells appear to regulate systemic metabolism. Swirski's team showed they do so by reducing levels of a protein called GLP-1, which normally increases metabolism by stimulating insulin secretion and glucose uptake.

"Swirski explained that the metabolism-suppressing role of β7-positive intraepithelial T cells might have developed to prevent starvation under conditions of nutrient scarcity. "At times when the availability of food is uncertain, it would be advantageous to have a system that converts some of the energy ingested with food into fat. But during times of over-nutrition, such a system can backfire and lead to the cardiovascular disease that is so prevalent today," he says."

Comment: This is just the first insight into how the body controls its metabolic rate.