People eat more food than they need for many reasons. Some people eat for comfort-to make themselves feel good. Some eat because of stress or fatigue. Others may mistake thirst for hunger.
The most likely reason people stop eating is because they feel full-not because they've consumed the appropriate number of calories. But regardless of why people eat or stop eating-or what types of food they eat-the basic rule concerning weight loss is the same: to lose weight, you must consume fewer calories than your energy needs each day.
It's helpful to understand the energy density of foods and how it relates to weight gain and weight loss. Some foods, such as desserts and processed foods, are high in energy density. This means that a small volume of that food has a large number of calories. Other foods, such as fruits and vegetables, have low energy density. They provide a larger portion size with a fewer number of calories.
So for the same number of calories, people can eat a larger volume of foods with low energy density than foods with high energy density. Foods with low energy density help people feel full while consuming fewer calories.
Researchers gave 20 obese and non-obese people as much food as they wanted to eat over five days. Their diet alternated between foods of low and high energy density. On the low energy density foods, the participants felt full by eating about half the calories they required to feel full on the high energy density foods.
Replacing foods high in energy density-high in calories relative to their weight or volume-with foods low in energy density can be an important part of a weight-management strategy. Foods high in energy density should be avoided or limited. They include high-fat foods such as butter, high-fat meats, cheese, and bacon, as well as low-moisture foods such as cookies and pastries. Foods with medium energy density include cooked grains, hard-boiled eggs, dried fruits, bagels, broiled meats, hummus, grape jelly, whole-wheat bread, and part-skim cheeses. Foods with low energy density have a very low calorie content per gram. Examples include most fruits and vegetables, broth-based soups, fat-free cottage cheese, and yogurt.
Fat increases the energy density of foods, while water and fiber decrease it by adding volume. Water has the greatest impact on energy density because it adds weight to food without increasing calories, reducing energy
density. So foods with a low energy density are usually those that are low in fat and high in water and fiber.
Fruits and vegetables, in their natural state, have a high water and fiber content and are low in fat, calories, and energy density. Fruit, especially when consumed whole, can enhance a feeling of fullness. Whole apples contain 60 grams of sugar and are 2.9 percent fiber. In the study they were associated with a higher feeling of fullness than were apple puree or fiber-free apple juice. Whole oranges are 2.5 percent fiber and whole grapes 1.3 percent fiber, and orange juice and grape juice are typically fiber-free, explaining why the whole forms of these fruits provide more of a feeling of fullness than juice. One 6-ounce serving of orange juice equals 85 calories versus the whole medium orange, which delivers only 65 calories and much more fiber and volume.
Vegetables also enhance a feeling of fullness if at least one cup of vegetables is consumed with a meal. Vegetables, like fruit, are high in fiber and water and reduce the energy density of the food. Vegetables are actually lower in calories than fruit, and substituting more vegetables than fruit for foods of higher energy density can be helpful in weight management.
Other benefits of eating fruits and vegetables include:
They provide fiber. Fiber recommendations are 15 grams per 1,000 calories consumed. High dietary fiber foods decrease the energy density of a meal and have been linked to weight regulation. Eating 14 grams of fiber a day was associated with an average weight loss of 4.2 pounds in four months.
They contain vitamins and minerals. Fruits and vegetables are packed with them. Increasing the intake of fruits and vegetables to approximately 2 cups per meal is the recommended goal to achieve optimal health as well as optimal weight.
They are low in fat. Other fiber-rich, low energy density foods include whole grains, nuts, and legumes, which are naturally low in saturated fat, trans fats, cholesterol, salt, and added sugars.
They fight disease. Consuming a diet of low energy density foods with a high daily intake of fruits and vegetables is associated with lower risks for numerous chronic diseases, including cancer and cardiovascular disease.
Cheryl Thomas-Peters is a registered dietitian and graduate student in a doctoral program in clinical nutrition. She has also authored four cookbooks. She lives in Napa Valley, California, where she and her husband own and operate a nutrition and lifestyle medical practice.