Are Increasing Portion Sizes and Ingestive Frequency Driving Obesity?

Scientific review published in Advances in Nutrition reports it is not clear whether portion size or ingestive frequency has a more prominent effect on energy intake or body weight

According to the World Health Organization (WHO), “obesity has reached epidemic proportions globally, with at least 2.8 million people dying each year as a result of being overweight or obese.”  In the United States, the Centers for Disease Control and Prevention (CDC) estimates that more than 40% of the adult population has obesity, placing them at higher risk for heart disease, stroke, type 2 diabetes, and certain types of cancer.

Weight gain occurs when total energy intake exceeds total energy expenditure.  Total energy intake can be broken down into portion size, the energy content of an eating event, and what researchers call ingestive frequency, the number of eating events per day, whether a full meal or a snack.  In recent decades, both portion size and ingestive frequency among adults have increased alongside the rise in obesity, suggesting that either increasing portion sizes or increasing ingestive frequency or both may underlie the rise in obesity.

Recently, a group of nutrition researchers, led by Kelly A. Higgins, a Research Nutritionist at the US Department of Agriculture (USDA) Agricultural Research Service (ARS), conducted a systematic scientific review and meta-analysis to independently assess the role of portion size and ingestive frequency in energy intake and body weight.  The results of their research, “Systematic Review and Meta-Analysis on the Effect of Portion Size and Ingestive Frequency on Energy Intake and Body Weight among Adults in Randomized Controlled Feeding Trials,” were published in Advances in Nutrition, the international review journal of the American Society for Nutrition.

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To conduct their research, the authors carried out a comprehensive search of the scientific literature in order to identify relevant randomized controlled trials.  A total of 9,708 scientific articles were initially found.  These were eventually pared down by a team of 10 researchers to 22 studies that met the authors’ inclusion criteria.

Following their analysis, the authors concluded “both larger portion sizes and increased ingestive frequency are associated with higher total daily energy intake in randomized controlled trials among healthy adults.”  In particular, evidence from randomized-controlled trials suggests that, compared with three ingestive events per day, six or more ingestive events per day are associated with an increased total daily energy intake of between 76 and 330 additional kilocalories per day.  In addition, larger portion sizes were associated with a net positive intake of 202 to 388 additional kilocalories per day.

Most of the randomized controlled trials that the authors investigated were of short duration, conducted over the course of seven days or less.  Given the short duration, the authors noted that “it is still unclear whether these differences in energy intake from increased portion size or additional ingestive events translate to either a clinically relevant gain in body weight or increased risk of developing other diseases associated with excess food and beverage intake.”

In addition, the authors stressed that “results from these meta-analyses cannot answer whether portion size or ingestive frequency has a more prominent effect on energy intake or body weight.”  In order to address this question, a study would need to hold portion size constant and allow study participants to self-select the number of meals they consume.  Conversely, the study would also need to hold ingestive frequency constant while portion size would be free to vary.  “This type of trial may provide insight into whether either portion size or ingestive frequency is a more potent contributor to excess energy intake.”