27 December 2018



INTRODUCTION Although it seems to be increasingly accepted that whole foods (such as lean meats, whole grains, fruits, and vegetables) should predominate one’s diet, the reasons given for this are often vague and not obviously based on scientific evidence. For example, it’s often stated that whole foods are ‘unprocessed’ and a good source of fiber…


Although it seems to be increasingly accepted that whole foods (such as lean meats, whole grains, fruits, and vegetables) should predominate one’s diet, the reasons given for this are often vague and not obviously based on scientific evidence. For example, it’s often stated that whole foods are ‘unprocessed’ and a good source of fiber and micronutrients, without a substantial explanation as to why these characteristics are desirable. Similarly, one might regard a food as either “good” or “bad” based on a combination of its macronutrient composition and the context in which it is being eaten, but not adequately account for the significance of other characteristics. Thus, while these views do have merit and can be useful tools in particular contexts, both fail to give a complete account of why some foods are generally better options than others.

In wanting to help give a more complete perspective toward evidence-based food selection, this series of articles is going to narrow the scope and explore the significance of energy density in particular. Before we do, however, we need to define a couple of terms that will allow you to fully understand the remainder of this article, and which will become increasingly relevant throughout the rest of this series.


Although one may find this an unattractive reality, a large part of our behavior today is still driven by ancient mammalian instincts. When it comes to food behavior, we naturally eat in episodes (i.e. meals and snacks) until we’re comfortably full, assuming sufficient food is present. We then voluntary terminate our food event; this point is called satiation, and is characterized by a lack of desire to continue eating and a sense of satisfaction, often accompanied by a general feeling of physical fullness. Following a meal – or, at least, following a truly satiating meal – some period of time elapses in which we do not desire to eat, a period in which hunger is suppressed and fullness is augmented. This phenomenon is called satiety. Thus, while satiation and satiety are undoubtedly similar, they are differentiated by the fact satiation is an immediate, during-meal effect which causes us to stop eating, while satiety is an extended, post-meal effect which causes us to continue to avoid eating for some time following a meal.

As satiety slowly declines after a meal, an underlying desire to eat determines our the timing of our next episode (again, assuming unlimited access to food); this phenomenon is called hunger. Although hunger can arise from different mechanisms, it’s important to note that feeling that you need to eat is technically not a starvation signal, as it doesn’t arise only in the context of true starvation; it’s not as if only unhealthily lean persons experience hunger. Instead, hunger is an absence of fullness in the stomach, and this occurs regardless of one’s energy status (in other words, regardless of whether or not one is maintaining, losing, or gaining weight). Throughout the remainder of this article, keep in mind that the “hunger” is being used specifically to refer to the subjective sensation of an absence of fullness in the stomach (which occurs transiently before eating), not hunger driven by homeostatic mechanisms (exemplified by the persistent hunger during an extended fat loss phase).

To better understand the relationship between satiation, satiety, hunger, and eating episodes, these phenomena can be graphed as occurring sequentially, as follows:

All of these terms fall under a broad categorization called appetite. When appetite increases, levels of satiation and satiety are decreased (or even absent) and levels of hunger are elevated. Intuitively, when appetite decreases, this usually means that satiation and satiety are elevated, while hunger is decreased or absent. Depending on the particular context, it’s desirable to either increase or decrease appetite, and thus when we use the term in this article, it’s typically in the context of appetite being either positively or negatively affected.
Now that we’re familiar with these common terms that are used to describe our internal feelings from a biological perspective, we want to shift our focus to one of the most important of food characteristics, and the main topic of this series: energy density.


Most simply, energy density is the amount of energy a food contains relative to its weight. For the sake of standardization and easy comparison between foods, energy density is usually discussed in terms of kcal/g, or kilocalorie per gram.

(Technical note: when you see the word “calorie” in discussions of food, this almost always refers to a kilocalorie, which is equivalent to 1000 ‘small’ calories. These “calories” can be differentiated from ‘small’ calories by capitalizing the c, creating “Calories”. However, for ease of comprehension, we’ll use “calorie” in place of “kilocalorie” or “Calorie” throughout this article – but keep in mind that doesn’t mean we’re referring to ‘small’ calories.)
So how does the energy density of food relate to our dietary behavior? We’ll explore some real-world, research-based examples, and their practical significance, in the next section. For now, let’s keep things simple and talk about hypothetical scenarios.

Let’s consider the example of apples versus peanut butter. According to the US Department of Agriculture (USDA), a medium apple weighs 182g, and contains 100 calories (kcal). Given energy density is usually rendered as kcal/g, all we need to do to determine the energy density of an apple is to divide its energy content by its weight, as follows: 100kcal/182g = 0.55kcal/g. On the other hand, smooth peanut butter (remember: smooth is better than crunchy!) contains 180 calories per 32g serving (approximately equivalent to two tablespoons). If we run the same calculation for peanut butter (180kcal/32g), we find that it has an energy density of 5.63kcal/g.

What are some of the implications of this difference in energy density? First, it means that on a by-weight basis, you get over ten times more calories from peanut butter than from an apple. From a more practical perspective, this means you could eat ten times the amount of apples, by weight, than peanut butter, and still have eaten about the same amount of calories.
To put it simply: this is a really, really, really big difference – and differences of this kind, applied across an entire diet, and compounded by time, can have powerful implications – especially in relation to common, highly significant goals like weight loss and health maintenance.

Stay tuned for part 2 to find out how.

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