October 5, 2020 Tuesday


By Jane E. Brody

What determines how much we eat and how much we weigh? Is it the amount of fat in foods, the presence of carbohydrates, the size of our portions, what we drink with our meals, that elusive trait called willpower? Conflicting popular advice can prompt would-be dieters to give up before they even start.

The good news based on solid research is that you can eat more - probably more food than you're now eating - and weigh less, if you choose more of the right kinds of foods.

At a recent meeting on the worldwide obesity epidemic, important insights into successful weight management were offered by Dr. Barbara J. Rolls, a professor of behavioral health at Penn State. She began her presentation on weight control with this irrefutable statement:

"Calories count, no matter what you read in the press. The laws of thermodynamics have not been reversed."

With respect to weight gain and loss, the laws of thermodynamics can be translated as: Calories consumed must be used or they will be stored as body fat. The body does not waste energy, no matter what its source. When people are placed on carefully controlled calorie-restricted diets, the amount of fat in the diet - whether 25 percent or 45 percent of calories - has little effect on weight loss, Dr. Rolls reported.

People who claim that they can eat as much as they want (of protein and fat, for example) and lose weight as long as they avoid certain kinds of foods (carbohydrates, for example) are really eating less (that is, fewer calories) than they did before.

But what about a majority of people concerned about weight control who are not interested in cutting out breads, cereals, grapes, bananas, watermelon, carrots, beets, potatoes, rice and pasta (not to mention wine, beer, cakes, cookies, ice cream and other carbohydrate-rich foods banned on Atkins-style diets)? Are they doomed to remaining hopelessly overweight?

Not according to Dr. Rolls, an expert on satiety and satiation, words that refer to what and how much a person has to eat at a meal to feel satisfied and stop eating. Many characteristics of foods affect satiety: how they look, taste and feel in the mouth; how much chewing they require; the nutrients they contain; how densely packed the calories are, and, independent of caloric density, the volume of food consumed.

She does not dispute the popular premise that the "macronutrients" in foods - protein, fat, carbohydrates, alcohol and fiber - influence caloric intake and use. For example, calorie for calorie, protein appears to be the most satiating nutrient. Furthermore, during overeating, the body burns more calories to metabolize protein and carbohydrates than it does when processing fats, which are the nutrients most efficiently stored as body fat.


So what makes your body say you've eaten enough? Dr. Rolls's studies on satiety have clearly demonstrated an overriding influence of food volume, prompting her to write an excellent book, "The Volumetrics Weight-Control Plan: Feel Full on Fewer Calories" (HarperCollins, 2000) with Robert A. Barnett.

She found that the amount of calories in a given volume of food makes a big difference in how many calories people consume at a given meal, and throughout the day. In nutritional parlance, this is called the energy density of the food. The greater the energy density - the more calories packed into a given weight or volume of food - the easier it is to overeat.

"People tend to eat a consistent weight of food," Dr. Rolls has found. When consuming a calorie-dense food high in fat, people are likely to eat more calories just to get in a satisfying amount of food.

What increases food volume without adding calories? You guessed it. Water. And what foods naturally contain the most water? You got that right too. Fruits and vegetables.

"People given the message to eat more fruits and vegetables lost significantly more weight than those told to eat less fat," Dr. Rolls said. "Advice to eat more is a lot more effective than advice to eat less. Positive messages about what can be eaten are more effective than restrictive messages about what not to eat."

"Water has the biggest impact on the amount of food we eat," she told an international symposium on the obesity epidemic held recently in Minneapolis. "Foods with a low moisture content increase the number of calories people eat."

What would fill you up faster - a quarter cup of raisins or one and three-quarters cups of grapes? Raisins are simply dried grapes; both contain the same macronutrients and supply the same 110 calories. The difference lies in volume - the amount of water they contain. If you ate a 475-calorie meal of soup, vegetables and fruit, you'd consume twice as much food by volume than if you chose drier, higher fat foods.

In her studies, people ate a constant weight of food, but if water contributed significantly to the weight and volume of the food, they ate about a third fewer calories. In one study, Dr. Rolls and colleagues tested the amount people ate when offered a 270-calorie chicken-and-rice casserole with a glass a water to drink, as opposed to the same ingredients prepared as a soup. The soup eaters spontaneously consumed 100 fewer calories, she reported.

In other studies, when participants were given a water-rich first course - soup or a salad, for example - before their main dish, they ate significantly fewer total calories than they did if the main course was given without the low-energy-density appetizer. In addition, study participants given foods containing lots of water and fiber ate less throughout the day.

Thus, by decreasing the energy density of foods, people naturally eat less, not just at an individual meal but all day long, Dr. Rolls reported. This was true of lean and obese participants in the study.

After water, which has zero calories, fiber contributes the most to food volume for the fewest number of calories. Fiber supplies 1.5 to 2.5 calories per gram, far fewer than fat, at 9 calories, or protein and carbohydrates, at 4 calories per gram. Also, fiber holds water in the digestive tract, which contributes to a more lasting sense of fullness.

Fiber is found only in plant foods: fruits, vegetables and grains, especially whole grains. Along with water, it acts as a digestive tract stimulant; cutting out fiber-rich foods can lead to chronic constipation.


Dr. Rolls's work helps to explain why so many people who reduced the fat in their diets failed to lose weight and perhaps even gained. She explained: "When the fat content of the diet is reduced but energy density is held constant, people do not decrease their caloric intake. But if energy density is reduced, no matter what the macronutrient composition, ad libitum intake declines."

That is, people eat less when there are fewer calories in a given volume of food. If you cut back on fat and replace it with energy-dense (that is, dry) carbohydrates like pretzels, crackers or sweets, you may not be reducing your caloric intake. You may, in fact, be increasing it.

Dr. Rolls's findings are good news for pasta lovers, who may be avoiding this food in response to the current mania for low-carb diets.

Start your meal with a salad or cup of soup, dish up a reasonable portion of pasta (a serving is but two ounces of dry pasta), and top it with lots of sauteed vegetables. With fruit and half a cup of frozen yogurt for dessert, you have a filling, nutritious meal that is not likely to add to your adipose depot and may even help you shed some extra pounds.



Want to receive notice of books, events, promotions, and news
of Barbara Rolls, PhD? Sign up now!

 HarperCollins Privacy Policy

HTML Text Only