Gluten-free diets can lead to deficiencies in nutrients such as vitamin B, folate and iron. Compared with regular bagels, gluten-free ones can have a quarter more calories, two and a half times the fat, half the fiber and twice the sugar. They also cost more.

The hullabaloo over gluten echoes the panic over MSG that began roughly half a century ago, and which has yet to fully subside. MSG, or monosodium glutamate, is nothing more than a single sodium atom added to glutamic acid — an amino acid that is a key part of the mechanism by which our cells create energy. Without it, all oxygen-dependent life as we know it would die.

A 1968 letter in The New England Journal of Medicine started the frenzy; the writer reported feeling numbness, weakness and palpitations after eating at a Chinese restaurant. A few limited studies followed, along with a spate of news articles. Before long, nutrition experts and consumer advocates such as Ralph Nader were calling for MSG to be banned. The Food and Drug Administration never had to step in; food companies saw the writing on the wall, and dropped MSG voluntarily.

Many people still wrongly believe that MSG is poison. We certainly don’t need MSG in our diet, but we also don’t need to waste effort avoiding it. Our aversion to it shows how susceptible we are to misinterpreting scientific research and how slow we are to update our thinking when better research becomes available. There’s no evidence that people suffer disproportionately from the afflictions — now ranging from headaches to asthma — that MSG-averse cultures commonly associate with this ingredient. In studies all over the world, the case against MSG just doesn’t hold up.

Too often, we fail to think critically about scientific evidence. Genetically modified organisms are perhaps the best example of this.

G.M.O.s are, in theory, one of our best bets for feeding the planet’s growing population. When a 2015 Pew poll asked Americans whether they thought it was generally safe or unsafe to eat modified foods, almost 60 percent said it was unsafe. The same poll asked scientists from the American Association for the Advancement of Science the same question. Only 11 percent of them thought G.M.O.s were unsafe.