Recently, four men and sixteen women with metabolic syndrome,weighing an average of 200 pounds, were put on the low carb SouthBeach diet for three months.
Although they were told to reduce theircarbs down to only ten percent of total calories in the first twoweeks and to keep them down to 27 percent in the remaining tenweeks, they didn't manage to follow the diet that strictly.
Infact, they ended up eating 25 percent carbs during the first phaseand 35 percent carbs during the second phase. Nevertheless, theylost an average of nearly ten pounds, and half of them no longer hadmetabolic syndrome by the end of the study.
To find out why and how this occurred, the researchers measured theproduction of hormones associated with appetite, including insulin,leptin, ghrelin, and cholecystokinin (CCK). CCK is agastrointestinal hormone that stimulates the digestion of fat andprotein and acts as a hunger suppressant.
Leptin is produced byadipose (fat) tissue; when it binds to brain receptors, it creates asense of fullness. Ghrelin, produced by the stomach lining,increases before meals and decreases after meals; it stimulatesappetite, working counter to leptin.
By the end of the first two weeks, insulin and leptin levels hadboth decreased. By the end of the second phase, insulin levelsapproached baseline again. Leptin levels, although they also rose,did not return to baseline.
By phase 2, fasting levels of ghrelinhad also increased significantly from baseline. After-meal increasesin CCK, however, were significantly greater than at the start of thestudy.
The researchers, led by Matthew Hayes of Pennsylvania StateUniversity, speculate that those ups and downs in hormone levelswork synergistically, allowing the low-carb diet to create a senseof satisfaction in spite of fewer calories.
As usual, they note thatfurther research is needed to underpin their speculations,especially when it comes to people without metabolic syndrome.
Sources: Journal of Nutrition, August 2007; Medline Plus