Large portions may contribute to weight gain

13 August 2007

Portion sizes of ready-to-eat foods and restaurant meals have steadily increased over the past decade. This has prompted concern from health educators because larger portion sizes may cause over-consumption of energy and weight gain. A new US study suggests that this analysis may be correct.

19 adult volunteers were given free pack lunches at their workplace over a two month period. For one month, the lunch box contained items totalling 767 calories. For a second month, the lunch box contained items totalling 1528 calories. The items were identical save for their portion size. The lunches were given in a randomised order with a 2-week break in-between.

The results showed that the volunteers consumed more calories at lunchtime when the larger lunch box was given. The extra calories were not compensated for over the course of the day so that, on average, the volunteers ate nearly 300 calories extra per day when using the larger lunch box. This translated into a mean weight gain of 0.64 kg over 4 weeks.

The authors concluded that offering larger portion sizes causes over-consumption of energy and that this can have a negative impact on weight.

For more information, see

Jeffery RW et al (2007). Effects of portion size on chronic energy intake. International Journal of Behavioral Nutrition and Physical Activity, Vol 4, pp 27 (open access journal).