Humans evolved in a calorie-poor environment, meaning that finding dinner wasn’t as easy as ordering delivery. In fact, for more than 99.9 percent of human evolutionary history, our ancestors were dependent upon what they could find in nature for food. Without reliable agriculture, humans were at the mercy of mother nature and luck, experiencing periods of starvation and excess. It was during these periods that humans evolved adaptations to endure extreme starvation. Those who survived—that’s us—are remarkably resilient at enduring life-limiting hunger.

So when you attempt to lose a few pounds by reducing your caloric intake, the body responds the way it has done for millennia—by slowing the metabolism, increasing hunger, and doing everything possible to acquire more calories. One study found that dieters experienced a 15 percent reduction in resting metabolic rate after a few weeks of conventional dieting—even after adjusting for the weight they lost. For the average person, this could mean the body is now burning 250 to 400 calories less just to stay alive. This is like your laptop reducing the screen brightness to save energy when the battery runs low. To make matters worse, those who are obese have greater reductions in their resting metabolism compared to those who are not obese, which makes things harder for those with the most to lose.

But there’s more: The body responds to dieting by increasing levels of ghrelin, the hunger hormone, to drive you to eat more. Ghrelin levels rise with additional weight loss, which is why dieters experience such intense cravings for food. Hunger is a stimulus so strong that psychologists have observed it impairing performance on basic memory tests.

Even still, dieting affects the brain in other ways to thwart meaningful weight loss. Eerily reminiscent of the waning judgement of an alcoholic, dieting can cause you to pick out foods that are calorie-dense, underestimate how many calories are in a meal before eating it, and think you’ve eaten less than you actually have. With so much compensatory chicanery, it’s no surprise that more than 82 percent of dieters are unsuccessful.

So how are some people—despite all the odds—keeping the weight off? Research shows that one of the best strategies hinges on the concept of calorie density. Calorie density is the amount of calories in a gram of food, which is important because humans eat a consistent weight of food from day to day. Knowing this, one could surmise that by eating lots of foods that are low in calories, one could lose weight. And you can, which makes sense from an evolutionary perspective; humans have been eating mostly low-calorie fruits, leaves, tubers, and vegetables for the better part of our ancestral history.

Paradoxically, by eating more food with
fewer calories, dieters were able
to lose weight and feel full at the same time.

Studies of low-calorie-density diets have found that people can reduce the amount of calories they need to eat to achieve satiety. In the first study to test this hypothesis, in 1983, participants eating a low-calorie-density, plant-based diet took in a mean 1,570 calories a day while those on a high-calorie-density diet took in 3,000 calories per day before feeling full. A later study showed that those committed to low-calorie-density, plant-based diets (which, in this study, happened to be a Hawaiian fare) could lose weight at a remarkable clip: an average of 17 pounds over 21 days. Long-term studies have shown that these results are maintainable.

By eating so few calories per day, dieters should have gone hungry, but they circumvented this problem by eating a larger volume of low-calorie foods. Paradoxically, by eating more food with fewer calories, dieters were able to lose weight and feel full at the same time. Low-calorie-density foods like legumes, fruits, and vegetables can help dieters avoid the siren call of hunger that can doom the best of intentions.

The proportion of plant foods eaten is an important facet of success. Eating more plants further lowers the calorie density of a diet and results in additional weight lost. Studies have shown that vegetarians, for example, eat 363 fewer calories per day than omnivores and have higher resting metabolic rates—up to 11 percent higher in some cases, which may be why vegetarians weigh less too.

For those not ready to become vegetarian, you don’t have to overhaul your entire diet. By feeding as few as three apples a day to human volunteers, researchers have still been able to show weight reductions. With results like that, eating an apple a day might keep the doctor away, but it might also help you lose weight.

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The Calorie Density Approach

Calorie density is simply a measure of how many calories are in a given weight of food, most often expressed as calories per pound. A food high in calorie density has a large number of calories in a small weight of food, whereas a food low in calorie density has much fewer calories in the same weight of food. Therefore, one can consume a larger portion of a low-calorie dense food than a high-calorie dense food for the same number of calories. On a day-to-day basis, people generally eat a similar amount of food, by weight.  Therefore, choosing foods with a lower calorie density allows us to consume our usual amount of food (or more) while reducing our caloric intake.

Foods low in calorie density also tend to be higher in satiety so by consuming foods lower in calorie density, one can fill up on much fewer calories without having to go hungry and without having to weigh, measure or portion control our food. In addition, the foods that are lower in calorie density (fruits, veggies, starchy vegetables, intact whole grains and legumes) are also the foods highest in nutrient density. Therefore, by following a diet lower in calorie density, one also automatically consumes a diet higher in nutrient density.

Principles of Calorie Density

• Hunger & Satiety. Whenever hungry, eat until you are comfortably full.  Don’t starve and don’t stuff yourself.
• Sequence Your Meals. Start all meals with a salad, soup, and/or fruit.
• Don’t Drink Your Calories. Avoid liquid calories.  Eat/chew your calories, don’t drink or liquefy them. Liquids have little if any satiety so they do not fill you up as much as solid foods of equal calories.
• Dilution is the Solution: Dilute Out High Calorie Dense Foods/Meals. Dilute the calorie density of your meals by filling 1/2 your plate (by visual volume) with intact whole grains, starchy vegetables, and/or legumes and the other half with vegetables and/or fruit.
• Be Aware of the Impact of Vegetables vs. Fat/Oil. Vegetables are the lowest in calorie density while fat and oil are the highest.  Therefore, adding vegetables to any dish will always lower the overall calorie density of a meal, while adding fat and oil will always raise the overall calorie density of a meal.
• Limit High Calorie Dense Foods. Limit (or avoid) foods that are higher in calorie density (dried fruit; high fat plant foods; processed whole grains; etc).  If you use them, incorporate them into meals that are made up of low calorie dense foods and think of them as a condiment to the meal. For example, add a few slices of avocado to a large salad, or add a few walnuts or raisins to a bowl of oatmeal and fruit.

What Are Calorie-Dense Foods?

Calorie Density Chart

Research has shown that people can freely eat foods that are 300 calories per pound or less and not gain weight. People can consume relatively large portions of foods that are between 300 and 800 calories per pound and still lose or maintain their weight depending on their individual activity levels and metabolism. The intake of foods with a calorie density of 800-1,800 should be limited as these can contribute to weight gain and interfere with efforts to lose weight. Additionally, the intake of foods over 1,800 calories per pound should be extremely limited as these foods can very easily contribute to weight gain and obesity and can also greatly interfere with efforts to lose weight.

The 2007 report from the American Cancer Institute and the World Cancer Research Fund recommended lowering the average calorie density of the American diet to 567 calories per pound. One can easily do this by following the above principles of calorie density, which allows us to eat freely of unrefined, unprocessed fruits, veggies, starchy veggies, intact whole grains and legumes without the addition of salt, sugar and/or fat/oil.

Summary

Calorie density really is a common-sense approach to sound nutrition and is the cornerstone of good health. It is the simplest way to lose and/or manage your weight for life. By following a few simple principles, you will increase the amount of food on your plate while decreasing your overall caloric intake, all without ever having to go hungry.  At the same time, you will be optimizing your overall nutrient intake.

This article was originally published on Jun. 19, 2012, and has been updated.

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