LONDON — Visitors to England right now, be warned. The big topic on people’s minds — from cabdrivers to corporate executives — is not Kate Middleton’s increasingly visible baby bump (though the craze does involve the size of one’s waistline), but rather a best-selling diet book that has sent the British into a fasting frenzy.

“The Fast Diet,” published in mid-January in Britain, could do the same in the United States if Americans eat it up. The United States edition arrived last week.

The book has held the No. 1 slot on Amazon’s British site nearly every day since its publication in January, according to Rebecca Nicolson, a founder of Short Books, the independent publishing company behind the sensation. “It is selling,” she said, “like hot cakes,” which coincidentally are something one can actually eat on this revolutionary diet.

With an alluring cover line that reads, “Lose Weight, Stay Healthy, Live Longer,” the premise of this latest weight-loss regimen — or “slimming” as the British call “dieting” — is intermittent fasting, or what has become known here as the 5:2 diet: five days of eating and drinking whatever you want, dispersed with two days of fasting.