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The Calorie Content of Foods:
A Scientific Breakthrough

A typical calorie chart shows the calorie content of foods by portion sizes, like a cup of rice or a large apple. For effective weight loss, we actually want to select foods with a low calorie density. What is calorie density? It is a way of finding good weight loss foods by checking how may calories they contain per ounce (or per pound or per 100 grams.)

Much of the research on calorie density was done at by Barbara Rolls, Ph.D.

She and a team of researchers have published dozens of studies on eating behavior.

They did their research at the Laboratory for the Study of Human Ingestive Behavior at Penn State.

Calories by weight of food

These researchers studied the foods people ate and they learned something interesting: a person eats about the same weight of food every day. This is true even though the calorie content of foods changes every day. There is something about the weight of food that fills our stomach and triggers feelings of satiety in our brain. 

But the calories in an ounce of one food can be very different from the calories in an ounce of a different food. The number of calories per ounce of a food is called the calorie density.

celery whole

An ounce of celery contains 4.5 calories and an ounce of peanut butter has 166.7 calories. The calorie density of celery is 4.5 and the calorie density of peanut butter is 166.7. Are they both low calorie foods? Definitely not. The celery certainly is. Peanut butter might be "low in calories" if you only eat one tenth of an ounce of it. But who can do that?  :-)

Scientists have done many studies to measure the calorie density of peoples' diets. They measure it the same way they measure the calorie density of a single food. They divide the calorie content of foods someone eats in a day by the number of ounces of food the person eats. The studies all show the same thing:

Calorie Density of Diet: Weight Loss or Gain:
Under 25 cal/oz All people lose weight, no matter how much food they eat.
25 - 37.5 cal/oz Most people lose weight.
37.5 - 50 cal/oz If people get some moderate exercise, they all lose weight.
50 - 75 cal/oz Everyone gains weight, except for people who get a lot of exercise.
Over 75 cal/oz Everyone gains weight.

How calorie density works

Suppose we eat one ounce of celery filled with one ounce of peanut butter. That makes 2 ounces of food containing a total of 171.2 calories (4.5 + 166.7). Divide by 2 and we have a snack with 85.6 calories per ounce. The calorie density is way too high and will contribute to weight gain.


Maybe we love peanut butter and we just have to have some with our celery. Let's say we get some exercise evey day and we want to keep our calorie density between 30 and 35. An ounce of peanut butter and 5 oz of celery would give us a calorie density of 31.5. That is a number we could live with....for a snack.

Cancer and calorie density

The American Institute for Cancer Research (AICR) recently released a report stating that overweight and obese people have a higher risk of cancer than normal weight people. They recommended that to avoid weight problems and cancer, we should keep the calorie density of our diet around 34.5 - 37.5 cal/oz.

Few people meet that requirement today. But in 1949 in Okinawa, nearly everyone did. The traditional Okinawan diet had a calorie density of 37.5 - 40.6 cal/oz.

sweet potatoes

The Okinawans were slender and healthy. They didn't know the calorie content of foods in their diet. Most of their calories (70%) came from sweet potatoes...they ate a lot of them! Only 8 percent of their calories came from fat. A sweet potato diet with some leafy greens, beans, and fruit would give us all the nutrients we need. And it would fill us up.

How to calculate calorie density

For packaged foods:
  • Look at the Nutrition Facts to find out how many ounces are in one serving. If the servings are measured in grams, divide the grams by 28.35 to get ounces. (Divide by 30 for a rough estimate.) Note: this only works if you are eating the food the way it comes out of the package. If you have to add water or other ingredients, the calorie density changes.

  • Divide calories by ounces.

For fresh foods or a specific recipe, here are two options:

But seriously, why bother to analyze fresh foods or recipes? You don't need to know the exact calorie content of foods you eat. Just eat mainly foods with a low calorie density: vegetables, fruits, legumes, and intact whole grains. Limit the foods that have a high calorie density, like nuts. You can use small portions to make creamy dressings or sauces.
 black beans rice salsa

Brown rice, beans, and salsa are all low calorie foods. This is a perfect weight loss meal as long as we don't add oil or avocado.

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