It is a topic I am pursuing, and I continue to be surprised at the dearth of studies. Barbara Rolls and colleagues have shown that portion size influences caloric intake; because prepared foods are often served in large portions, it seems likely that they promote excessive caloric intake and weight gain. But we need more research to make the connection between prepared foods and weight gain.
Further complicating the picture is the huge number of foods that fall under the term "prepared" or "semi-prepared"--and because people are cooking less and less, their very idea of what a prepared food
may be changing. Putting pasta sauce from a jar on cooked spaghetti may or may not be considered using prepared foods, depending on the perspective of the "cook."
Further complicating things is the many foods like macaroni and cheese that can be made at home either from scratch or from a mix--or bought as a ready-to-eat dish. Unfortunately, most epidemiologic studies that follow people's diets and weights over time don't collect the details that would allow the authors to differentiate between what was made from scratch and foods at least semi-prepared outside the home. This may explain why there is so little research on the association between prepared foods and obesity.
Even if we do not yet have studies connecting the reliance on prepared foods--other than fast food--to weight gain, there
a lot to support the idea that the two are related. One of the most powerful ways people learn is by observing others. In the past, not only did children, particularly girls, learn to cook from their mothers, but also they learned the general steps involved in cooking. That includes learning about the ingredients used to make meals. Relying increasingly on prepared and semi-prepared foods can lead to raising generations who have, at best, a vague idea of what they are eating, and set them up for eating a diet too high in calories and too low in fiber.
For those of us trying to prevent or treat obesity, the reliance on prepared foods is also of concern because getting people to change what they eat is much harder if they don't cook in the first place. It is a much bigger change to ask someone to start making their own dinner from scratch than asking someone who already cooks to change the number of tablespoons or the type of fat they use in their cooking.
We have a ways to go before we better understand what motivates someone to cook from scratch versus with some prepared ingredients versus buying prepared meals, and we need studies that link these types of food preparation to obesity. In the meantime, I think we should still encourage men and women to get into the kitchen and take greater control of what they eat--and limit dietary outsourcing.
This is one of the priorities I've made in my own family, and it's already paying dividends. Recently, when our babysitter asked my daughter, Sofia, what she wanted for lunch, Sofia opened the cabinet and pulled out olive oil and garlic. She knew that the first step in most things I cook involve sautÃ©ing garlic in olive oil.