But can it really help you slim down? We asked Reveal's Dr Phil Hammond who set the record straight…
"No. There was a theory that if you drink lots of water it will fill your stomach up and make you less hungry. And if the water is ice cold, your body then burns calories to warm it up to body temperature.
Sadly, this doesn't seem to work, probably because the water passes through your stomach quickly and doesn't hang around long enough to make you feel full.
A much better bet is a thick soup made from healthy vegetables, pulses and beans. That will fill you up and give you energy."
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