I have not been able to read the original study, but I suspect they are not talking about 21 year old co-eds as much as widowers and divorced men. In any case, learning to cook is always a good idea!

Yeah, this sounds like widowers and divorced men:

For an analysis published in the journal Nutrition Reviews, researchers at Queensland University of Technology looked at 41 studies and found that, compared to people who live with others, bachelors and bachelorettes ate fewer fruits, vegetables, and fish and had lower food diversity overall. Unsurprisingly, men living alone were more likely than women to have unhealthy diets. Katherine Hanna, Ph.D., said in a release that people who live alone may lack motivation to shop for groceries or cook (or lack cooking skills altogether) and that often leads them to prepare "simple or ready-made meals lacking key nutrients." Pizza, she means pizza.