I haven't actually read Marion Nestle's Why Calories Count yet, but I am getting the gist of it through her great blog, Food Politics. Now I'm sure you already know about my fascination with the history of calories and food politics, as I previously wrote about. So I can't wait to get her book!
In a recent post, Nestle writes,
If you want to understand calories, you need to know the difference between calories measured and estimated. Most studies of diet, health, and calorie balance depend on self reports of dietary intake and physical activity or educated guesses about the number of calories involved. Most diet studies rely on estimates. When it comes to anything about calories in food or in the body, you have to get used to working with imprecise numbers. That is why it works better to eat smaller portions than to try to count calories in food. Even small differences in the weight of food will throw calorie estimations off. [emphasis added]This struck a chord with a recent class discussion. We were discussing democratizing science, and our instructor referenced a concept developed by Donald Mackenzie in his book, Inventing Accuracy, which is the "certainty trough." People extremely close to an issue, likely scientists, perceive the exact uncertainties of the issue. A great analog here is climate scientists, who are very careful to not underestimate the uncertainty associated with climate change. But others involved in the climate regime, such as practitioners and activists, perceive a lower uncertainty- they are in the "certainty trough." To outsiders, uncertainty is perceived as even higher- for example, climate might be seen as an "act of God" or a random event like weather. Also, there are actors manufacturing and exploiting uncertainty, as Naomi Oreskes and Erik Conway show in their book, Merchants of Doubt.
So as Nestle says, for food practitioners, i.e. anyone who eats, "you have to get used to working with imprecise numbers." No matter how much nutritional scientists narrow down the science of metabolism, it is still highly dependent on biological factors unique to our own bodies. Food and diet are a series of constant experiments where we must embrace uncertainty.
This concept of embracing uncertainty applies to more than just food consumption, but also to other parts of the food system. I've been working on publishing a factsheet on greenhouse gas emissions from food systems, and the truth is, there is a high degree of uncertainty within the system, making it very difficult to get an exact measurement of the "food miles" or "carbon footprint" of any one food. But this shouldn't paralyze us from making common sense changes, be it in our diet (eat less meat, buy less packaged/processed food, buy only what you will eat) or in our agricultural and commercial processes. As Nestle suggests, "get organized; get motivated... eat less, move more, eat better and get political."