The scientific name for anti-fat bias is weight stigma (a.k.a. fat stigma or fatphobia), and experiencing it has been l inked to increases in risks of type 2 diabetes, hypertension, cardiovascular disease, and mortality, as well as depression, anxiety and low self-esteem. In fact, a 2017 study published in the Annals of Behavioral Medicine found that weight stigma posed a greater overall health risk than what people ate, and about an equal risk as physical inactivity. Given that weight stigma tends to lead both adults and kids to avoid physical activity, weight stigma can take a double toll on people’s health.

Moreover, weight stigma isn’t just limited to overt nastiness and bullying. For example, several studies have found that merely reading news reports about the supposed health risks of larger body size leads to greater anti-fat prejudice. (Those results held true even when the reports included an explicit anti-weight-stigma message.) A 2017 study in adult women found that those whose parents had commented on their weight in childhood reported greater body dissatisfaction years later, regardless of their actual B.M.I. And a 2014 study found that young women who were told in an experiment that their weights “weren’t ideal” experienced higher levels of cortisol (the stress hormone), regardless of their actual size.

Should you think that the solution to weight stigma is simply to lose weight, remember the data we just discussed on the ineffectiveness of weight-loss efforts. We simply don’t know of a way for more than a tiny fraction of people to lose weight and keep it off long term — and that’s just as true for WW’s new app as it is for any other diet or lifestyle change.

[For more on healthy eating for kids, check out NYT Parenting about Kurbo by WW and more.]

Another common harmful effect of dieting is disordered eating, for people of all ages. It’s especially common for kids to interpret even the most seemingly benign messages about “healthy eating” in strict ways; indeed, most of the clients I’ve treated for eating disorders or subclinical disordered eating had their disorders triggered or exacerbated by messages they learned about food and weight in childhood. More than 55 percent of high school girls and 30 percent of boys report engaging in harmful practices including fasting, taking diet pills, vomiting and abusing laxatives to lose weight. As many as 60 percent of 6- to 12-year-old girls are worried about their weight.

WW has described the app as a “holistic tool,” not a diet, but the way it’s been branded doesn’t change the effect it could have on its users. Programs like this are fertile ground for disordered eating, encouraging kids to track what they eat using a “traffic light” system that divides foods into red, yellow and green categories, implicitly coding certain foods as “good” and others as “bad.”

Efforts to lose weight are likely to be ineffective and can be harmful to people of all ages, but they are especially troubling when imposed on children who aren’t in a position to make their own choices and who haven’t had the opportunity to develop a peaceful relationship with food and their bodies.

Sophia Carter-Kahn was one of those kids who was put on a diet. Now in her late 20s, Ms. Carter-Kahn started going to Weight Watchers around age 10, after a doctor told her she needed to lose weight. As she told me on my podcast, Food Psych, in 2018, all the rules and numbers she learned at Weight Watchers led her to obsess about food in a way that was incredibly disordered. Those patterns took years to overcome.