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Old 05-05-2016, 02:24 PM   #9
Tad
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Location: Ontario, Canada
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There actually have been studies on the impact of yo-yo dieting. Maybe not a ton of studies or on huge population samples, so perhaps we are at more the 'some evidence of' rather than 'conclusively proven' stage, but IIRC correctly what I've read is:
people who had more than one cycle of large weight loss showed ~30% weaker immune response, even many years later, compared to people who have only had one or none.

With respect to The Biggest Loser, the report I heard about the above said that they'd looked at metabolic rates of former contestants, some years after the show, and they were low compared to typical people of their weight -- while they had been typical before taking part in the show.

Given that our immune response is one of the many baseline systems which consume energy all of the time, these seem fairly consistent -- enough 'starvation' (multiple cycles, or a really extreme case) causes the body to decide it should save resources permanently. This isn't just some magical switch -- it means growing less new cells, having a less vigorous immune response, and various other things. It is like deciding to save money in a building by turning down the heat, not having the cleaning service in as often, not being as aggrsesive about repairing things, etc.
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