A study warns that if you are watching your waistline, there might not be a lot of joy in cooking.

Research published in the February 2009 issue of Annals of Internal Medicine finds that restaurants aren’t the only ones who’ve supersized portions. Cookbook recipes are also to blame.

“It’s a dangerous misperception because it leads us to drop our own vigilance when it comes to our own kitchens and dining rooms,” said Cornell University marketing professor Brian Wansink, PhD, and author of Mindless Eating: Why We Eat More Than We Think (Bantam 2007).

He directed the study that found the trend in several cookbooks, but focused on the Joy of Cooking (Scribner 2006), because it’s an icon, had a stable editorial direction over decades and allowed for recipes to be tracked through the years. The book, first published in the 1930s, was updated about every ten years – most recently in 2006.

Eighteen classic American recipes were published in all seven editions of the cooking manual and calories per serving increased in 17 of the 18, because of changes in ingredients and serving size. The average calorie increase was 35.2 percent over the 70 years.

Chili con carne was the only recipe to stay the same. But chicken gumbo, for example, which made 14 servings of 228 calories a piece in 1936, produced 10 servings of 576 calories in 2006. Brownies went from 103 calories in 1936 to 147 in 2006 – a 40% jump – and tapioca pudding went from 154 calories in 1936 to 223 in 2006.

Total calorie content went up in 14 of the 18 recipes, and the increase in overall calories happened in spurts. The first jump was in the late 40s, followed by another in the early 60s, and the biggest increase (33.2%) was in the most recent 2006 edition.

Wansink says he is more concerned by this increase in overall calories per recipe than in portion size.

“Those are things that are a little bit hidden from us,” he explained. “You notice a big or small portion, but it’s harder to tell if some things are really caloric or not. A couple more teaspoons of butter in the goulash are much more hidden than just having more goulash.”

Researchers believe some of the change is due to the fact that food is cheaper now than it was 70 years ago, so recipes have more meat and fewer ingredients like beans or vegetables – which are not only cheaper, but also lower in calories.

Wansink admits there is one limitation of his study – it measures written recipes, not what people eat.

But Marion Nestle a professor of nutrition, food studies and public health at New York University and author of Food Politics: How the Food Industry Influences Nutrition and Health (University of California Press 2007), says this research is an expanded version of other studies that have shown an increase in portion sizes across the entire spectrum of food.

“It’s driven by both supply and demand,” Nestle said. “People love a bargain. Because the cost of basic food ingredients is so low relative to the costs of labor, rent, packaging, and other such things, companies could increase the amount of food served and make a profit on it.”

She says this study clearly shows that many factors in our environment – particularly portion size, but also plate size, cup size and how close food is to you – influence the amount we eat. And she says most aren’t aware of this influence.

“This means we either have to become conscious, which is difficult for most people and not much fun, or change the influences,” Nestle said. “I’m for changing the influences. How about getting food companies and restaurants to give a price break for smaller portions, make smaller-size portions, and serve foods on smaller plates? All of those would help.”

Wansink says when eating in, families also need to downsize their serving size and calorie composition of meals if they want to avoid obesity.

“The big takeaway is that if you are making a dish from a recipe like this, you need to remember that when recipes were established, there were 7 or 8 people in the family, not 3 or 4,” he said. “What we recommend is when you make a dish like this, immediately cut it in half and pack it up right away so you don’t continue to eat and eat and eat. And then you have something good for later in the week."