We evolved in an environment that forced us to seek very particular types of food: ones that provided many calories from little volume. This was because our food environment was scarce. As a consequence of this food scarcity, we would cycle between long periods of fasting and occasional feasting. Nowadays, we've retained the tendency to seek out energy-dense food. The only problem is that we live in a different world. A world where food is ubiquitous, affordable and engineered for overconsumption.
How did this come to be? And what can we do about it? To answer these questions, we must first consider the concept of energy density.
ENERGY DENSITY 101
Energy density is defined as the amount of energy per unit weight (be it a gram or a pound) of a food or beverage. For example, 10 grams of ice cream is more energy dense than 10 grams of lettuce leaves. Why is that? There are a few answers.
First, the macronutrient composition of a food affects its density. Protein and carbohydrate yield 4 calories per gram. Fat yields 9 calories per gram. So a food with more fat than protein or carbohydrate will be more energy-dense.
Second, fiber content. Fiber is a type of carbohydrate found in certain plant foods. However, it cannot be fully digested and absorbed by the body. For this reason, foods that have a high total proportion of fiber are less dense than those with a low total proportion of fiber.
Third, water content. Water has no calories, and its presence adds weight and volume to a food without increasing calorific yield. Thus, high water content will lower energy density.
Fourth, processing. Almost all the food available to us has undergone some form of processing. The freezing of produce in transit, the adding of sugar or salt, and the removing of fat, fiber and water all count as processing. Processed food is generally cheaper to purchase and simpler to consume, but there is a cost associated with it. Generally speaking, the more processed a food is, the higher the energy density it will have.
THE REAL PROBLEM
With the concept of energy density and the factors that increase or decrease it in mind, it becomes possible to reframe many of the problems surrounding diet and nutrition. Perhaps it's not that human nature has changed dramatically, or that we are weak-minded creatures unable to stop ourselves from eating constantly? Perhaps it is that the environment we live in has evolved so rapidly.
Energy-dense food is cheap, available practically everywhere (from the supermarket to the gas station), and so so easy to rely on when you have little time to prepare whole foods. And when you add in liquid calories from alcohol and from other sugar-laden beverages, it becomes clear that one of the main problems with what we eat and drink is energy density. It is very, very high.
KNOCKING DOWN DENSITY
Sometimes, when people think of nutrition and diet, they think of macronutrients and micronutrients. But for most, the word that comes immediately after "diet" is "calories". The word that few people think of is "volume".
A rule of thumb is that humans tend to eat the same volume of food per day. After all, some of the first signals our stomach communicates to our brain regarding satiation are related to volume, not energy absorption. This is why we can eat a tub of ice cream and still feel ravenous--sure, there are thousands of calories in that tub, but in terms of volume, it's not that much. But eat seven apples in a row and you'll probably feel satisfied--and very bored of apples.
So, what can we do? Answer: eat less by eating more.
Trade density for volume. Build meals around fruits and vegetables: as a consequence, we will consume more in terms of volume but less in terms of calories. Feel snack-ish? Just eat fruit until we don't feel snack-ish anymore. Eyeing up a big glass of orange juice for breakfast? Pause. Drink 500ml of water and then see how you feel about that orange juice. Super size fries and cola? Not recommended. But not if the food has a low energy density. Super size salad, an extra banana or another handful of berries? Go for it.