U.S. Department of Health and Human Services

Tracking both the what and the when of the human diet

Researchers have developed an innovative smartphone application (“app”) to provide valuable insights into the content and timing of the human diet, and showed that many adults eat over a span of 15 hours or more each day; through a very small pilot study, they have also begun to explore whether limiting the hours of daily eating and drinking may help achieve weight loss.  Measuring just what people normally eat and drink during their daily lives is surprisingly difficult.  Standard approaches, such as surveys or food diaries, depend on accurate recollection and measurement by study participants, and can be a significant burden, particularly if a person wishes to indulge in between-meal snacks.  Further, research suggests that when people eat—not just what—may have a significant impact on metabolic health: shift workers have a higher burden of obesity and diabetes; and in animals, 24-hour access to food promotes poorer metabolic health.  To get a clearer idea both of what people eat and when, the new study took advantage of smartphone technology.  Participants—156 healthy adult men and women—were asked to use the cameras on their phones to take pictures of everything they ate or drank, regardless of calorie content (including water), for 3 weeks.  None of the participants were shift-workers.  An app specially designed for the study logged the date and time of each picture, and sent the image to study researchers for analysis.  The image was then automatically deleted from the smartphone to prevent it from later influencing the participant’s eating, and to reduce memory-hogging on his or her device.  An estimated caloric value of each item was recorded by study staff.  (Participants who forgot to take a picture before they took a bite were asked to submit information via text entry.)  If participants didn’t finish an item, they submitted a second picture showing the leftovers.  This part of the study was designed to better understand how people eat: the participants received no dietary guidance.

Results showed that although the majority of participants described themselves as three-meal-a-day eaters, the actual number of times people consumed calories varied substantially, averaging from a little more than 3 to a little more than 10.  The median portion of the day during which people ate was nearly 15 hours (i.e., one half of participants generally ate during a shorter period of the day than that, and one half during a longer one).  The study also found that consumption was generally heaviest in the evening hours: less than one-quarter of calories were typically consumed before noon, while over one-third were typically consumed after 6 p.m.  The average weight of the subjects remained quite stable over the course of the study; this suggests the simple act of taking the pictures and using the app did not induce participants to make significant changes in their eating habits.  However, there are some important caveats: the study was relatively short, and the participants relatively young (average age about 28) and not especially diverse—more than three-fourths of the group were either non-Hispanic white or of Asian descent.  Thus, it will be important to learn whether the observed eating patterns are similar to those that would be found in a more representative cohort of Americans. 

Because experiments in animal models have shown that reducing food availability to 12 hours or less may have metabolic benefits, the researchers sought to test whether this might work in people.  They began with a very preliminary study of just a few people, to see whether such a test would be feasible.  They recruited eight participants (five men, three women) from the first study who consumed calories for 14 hours or more per day and who were also overweight or obese to participate in a 16-week follow-up study.  These eight people were asked to confine consumption of calories to a consistent 10- to 12-hour window that they themselves were allowed to select.  They were instructed to stick to their chosen window, but given no guidance about what kinds of things they should eat and drink, or how much.  All eight significantly reduced their eating period—by an average of more than 4.5 hours.  Although they were not counseled to eat less, they also consumed 20 percent fewer calories, on average, and most of the people lost several pounds.  At the same time, they reported feeling they had more energy, reduced hunger at bedtime, and better sleep satisfaction.  Notably, all of the participants expressed interest in continuing this approach, and all of these improvements generally persisted for at least a year, 8 months after the active phase of the intervention had ended.  Follow-up studies with larger numbers of people will be needed to confirm these preliminary findings, and to see whether this sort of intervention might be effective in a more diverse group of people.  If so, shortening the period of daily caloric intake may turn out to be a valuable approach to helping people lose weight and potentially improve other aspects of their health.  In the publication of their study findings, the researchers noted that they are continuing to gather data using the app, and provided information for people interested in their research to learn more and, if they wish, sign up to participate.

Gill S and Panda S. A smartphone app reveals erratic diurnal eating patterns in humans that can be modulated for health benefits. Cell Metab 22: 789-798, 2015.