Combine Two Approaches for Weight Control

Summarized by Robert W. Griffith, MD
March 27, 2006

Introduction

'Energy in' (food) minus 'energy out' (exercise) = weight gain, in many cases. So, one way to control one's weight is to reduce energy intake. And there are two ways to do this: portion size control, and energy density reduction (i.e. eating less calorie-rich foods). Now researchers at Pennsylvania State University have studied the benefits of combining both these methods in a group of volunteers. They've publish their findings in the American Journal of Clinical Nutrition, and we summarize them here.

What was done

There were 24 healthy female volunteers aged 19-35, who weren't following any diet, were not in training or pregnant, and were not taking medications that might affect their appetite or food intake. They didn't smoke, and ate 3 meals regularly every day.

Each participant took part in 4 distinct 2-day sessions, separated by at least one week; this represented a cross-over design. The same 2 daily menus with the same food items were served at each session. However, the portion size and the energy density of the foods were changed, according to the table below:

	75% Energy Density	100% Energy Density
75% Portion Size
Weight (calories/day)	1530	1530
Density (calories/gm food)	1.61	2.11
100% Portion Size
Weight (calories/day)	2040	2040
Density (calories/gm food)	1.61	2.11

This way, each participant had 4 different 2-day sessions: low-portion low-density, low-portion full density, low-density full portion, and full-density full-portion. The order of their sessions was allocated at random.

Water was the only beverage allowed, except for additional tea or coffee at breakfast. The meals were served and eaten in the laboratory, except for an evening snack, which the participants took home with them. Subjects were allowed to eat as much of the food supplied as they wanted. Physical activity was kept level during the study. Before and after each meal the participants rated their hunger, fullness, and appetite levels.

What was found

The average age of the 24 women was 22, and their average BMI was 22.6 (i.e. in the normal range). They showed no differences in their ratings of hunger and fullness over the range of meals consumed on the session days.

It was found that a 25% decrease in portion size led to an average 10% decrease in energy intake - 231 calories/day. A 25% decrease in energy density, however, led to a 24% decrease in energy intake - 575 calories/day.

Clearly, reducing energy density of food was more effective than reducing portion size. However, when both steps were done in the low-portion low-density sessions, there was a 32.5% decrease in energy intake - equivalent to an average of 812 calories/day.

What this means

This study shows how two separate measures to reduce energy intake can be employed at the same time, each producing effects that, added together, are substantial. A 25% reduction in portion size may be obvious to individuals, but it was not associated with increased hunger or decreased fullness in this study. And a 25% reduction in the density of food - achieved mostly by reducing the fat content - was hardly noticeable to the participants. It might be best for people planning to cut their energy intake (i.e. lowering their 'calories in') to begin by cutting down on fat, and then proceeding to reduce portion size as a second step. Following such a regime for a period will almost certainly lead to weight loss. Smaller than 25% reductions in both factors will allow weight control, if not weight loss.

Source

• Reductions in portion size and energy density of foods are additive and lead to sustained decreases in energy intake. BJ. Rolls, LS. Roe, JS. Meengs, Am J Clin Nutr, 2006, vol. 83, pp. 11--17

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