It’s energy density, the number of calories in a particular weight (or volume) of food.
I know, there’s that word! Calories! But since the very definition of weight loss is expending more calories than you absorb, it should probably at least be part of your vocabulary. Besides, this isn’t about counting them. It’s about eating them in the most satiating way possible.
Energy density is the basis of the Volumetrics series of diet books, by Pennsylvania State University nutrition professor Barbara Rolls, and it’s a diet concept that has been around forever. “A lot of the stuff we do, it’s ‘My grandmother could have told you that!’ ” Rolls told me of the studies she runs in her lab.
That work focuses on how foods that have a lot of bulk for the calories they deliver can satiate better, and lead to lower overall consumption, than foods that are more calorie-dense. It works because, as your grandmother could have told you, it fills you up. If Captain Obvious needed a diet, this would be it.
It’s not just the physical sensation, of course; your endocrine system also gets into the act with its satiety signals. And you get a big assist from your brain, which tends to calibrate “enough” by sight. Take the Wheaties experiment, for example.
One of the challenges in testing whether a food’s volume makes a difference in consumption is finding foods that are exactly the same, except for volume. But crunchy cereal flakes offer just such an opportunity, because they can be crushed to be almost any volume you like.
In Rolls’s experiment, her team crushed the Wheaties to 80 percent, 60 percent and 40 percent of their original full-flake volume, and let subjects take their own serving. All subjects estimated they ate about the same number of calories, but their intake went up significantly as volume went down. The subjects who got the 40 percent cereal ate a third more — despite the fact that crushed cereal isn’t really very appetizing.
Ice cream is, though, and one study gave subjects snacks of low-fat or full-fat ice cream, thereby varying the energy density but not the volume (the inverse of the Wheaties study).
They rated the ice creams as equally palatable, but ate 139 fewer calories of the low-fat version and didn’t compensate by eating more later in the day. And before you splutter that only a philistine can’t tell low-fat from full-fat ice cream, let me inform you that these particular subjects were French. C’est vrai.
It works with kids and mac and cheese. It works when you add a salad to a meal as a first course. There are a gajillion studies that pit foods with lower energy density (which the literature rather unfortunately abbreviates ED) against foods with higher levels. And, according to Rolls, the upshot is that people eat fewer calories of the less-dense food, and they don’t tend to make it up later.
These studies, though, are all done in labs with food that’s manipulated surreptitiously, and that doesn’t mimic what goes on in most people’s homes. Out in the real world, there’s some evidence that people who eat diets low in energy density take in fewer calories (and also lose more weight in diet trials), but it’s hard to draw conclusions from that. A diet that’s calorie-sparse is heavy on the veg, light on the desserts, and that kind of diet is probably a marker for overall prudence and health-mindedness. It could be the prudence, and not the energy density, that’s responsible. My best guess, which is also Rolls’, is that it’s a combination of both.
I like energy density because it’s the Unitarianism of diets. It doesn’t prescribe specific foods and it co-exists with just about all the other diets. Almost regardless of how you’re eating — low-carb, keto, low-fat, paleo — you can focus on whichever foods in those diets are low in calorie density. As an adjunct to other diets, it can amplify their effect. (Speaking of which, I know I promised you a keto column last month, but I’m waiting for the results of a big study to be released.)
Three things help make foods less calorie-dense:
Water: It’s obviously the key to the satiating power of soup. And, weirdly, drinking water with your food doesn’t have the same effect as cooking the water into your food, Rolls said (okay, she didn’t say “weirdly,” but the rest of it). Liquids you drink tend to move through you pretty quickly, without the chance to make you feel full.
Water is also the reason vegetables, even the starchier ones, have bulk without many calories. Cooked pasta is 62 percent water, and it has 157 calories in 100 grams. Cooked sweet potatoes are 80 percent water, and half the calories.
If you come here often, you know that, from an environmental perspective, I’m no fan of salad. Its water content (96 percent, for crispy lettuces like iceberg) means it yields precious little actual food for all the resources it takes to grow and transport, but that’s exactly why it’s a dietary win. Food is just a never-ending series of trade-offs.
Fiber: It bulks food up with carbohydrates that are hard for your body to digest, so they deliver only about half the calories of easily digested carbs. For most foods, it’s not a huge calorie-density win, but fiber can also contribute to satiation by slowing down digestion.
Air: Obviously, no calories at all. Fluffy foods like puffed cereals, popcorn and my personal favorite, souffles, look like they’re more food than they are and can outwit your cognitive calibration system.
Although you can also reduce calorie density by cutting fat, I prefer adding to subtracting. Adding veg to almost anything — stews, sauces, sautes — just makes more of it. Soups and souffles are at home on any table, festive or workaday. Big helpings of those make it easier to have smaller helpings of, say, the pecan pie.
I started writing about nutrition in the ’90s, and I could have written a column like this then (although I like to think I’ve increased the deathlessness of my prose). But I’m writing it now because it was true then, it’s still true, and we’ve lost sight of it. Theories about satiety that are much more complex — all macronutrients all the time — got currency, and the funding followed. Most of the research on the Captain Obvious Diet dates back 15 years or more.
It’s easy to see why: We kept getting fat. Which demonstrates what we ought to know about weight loss by now, which is that it’s hard. There’s no strategy that’s sure to help you get thin; if you want a guarantee, buy a toaster. But if you want to make it just a little easier to eat what you intend to, and no more, pump up the volume.
If you don’t believe me, go ask your grandmother.
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