If Why Calories Count eventually draws conclusions and dietary recommendations that now seem obvious and redundant, Marion Nestle and Malden Nesheim nonetheless approach the importance of calories in a thorough, well-thought analysis of what can be scientifically proven and what is just supposition. The book addresses several facets of calories: how scientists measure their use, why everyone needs them, how the body gauges the amount it needs and the results of any discrepancies in this amount (due to an excess or lack of calories), and finally the politics of how we know (or more often, don’t know) the number of calories in the food we consume.

The book’s conclusions to monitor your weight, eat less and better, move more, and beware of marketing pitfalls, which today are well-known to anyone who makes the effort to listen, are on the whole unremarkable. Nestle and Nesheim themselves admit that by now, “this is old news” (p.217). However, in the six preceding parts, Nestle and Nesheim make it clear that they never sought to write a diet book. Instead, they raise an interesting discussion on why some people appear to eat everything in sight and maintain a stable weight and why others struggle against obesity. In a socially constructed environment designed to make us eat more, it has become more difficult to listen to bodily signals. Obesity is a global problem, they write, with a sequence of baby steps as the best solution.

The discussion in Part 1 regarding how scientists measure the calories contained in foods and the calories expended by a human to maintain his basal metabolism, plus any additional spontaneous exercise, is informative to the genuinely interested. Through the development of the Atwater values for estimating the calories in protein, fat, and carbohydrate, and testing of human expenditure through the modern calorimeter, we see how the USDA’s recommended 2,000-calorie diet is produced as a “good enough” average of what the human body needs. “Good enough” prevails as a theme, emphasizing that almost every number is merely an estimate. While this is frustrating to anyone trying to track his calories, Nestle and Nesheim present estimates in a thoughtful manner, at times chuckle-worthy but never cavalier.

The book is valuable in its thoroughness and its approachability, as many find discussions of calories so confusing that they opt to not pay any attention, a trap that often leads to overconsumption. Its attention to the “secret calories”—most notably alcohol, to which several chapters are devoted; genetics—which mainly comes down to a tendency to “fidget” more than others (a beneficial tendency, regardless of what your mother once told you); and the ability of social environment to overcome body signals of fullness, are of particular note.

—Heather Hammel