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Human eating patterns ... there’s an app for that

Eating throughout the day has become quite normal, given the ubiquitous availability of snack foods. Partly due to this, diet research has been plagued by inaccurate self-reports. This study used an app to get around that issue.

Study under review: A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits

Introduction

The “city that never sleeps” may have originally referred to New York City, but cable television, the Internet, and countless 24-hour food options have allowed people in nearly any city to live a 24/7 lifestyle. Along with this lifestyle comes a greater likelihood of eating increasing amounts of food later in the evening.

Among the many reasons this can impact weight gain are the effects of food timing on thermogenic response[1] to a meal. These effects are due to [2]circadian rhythms[2], or our internal body clock, which synchronize the daily patterns of metabolic activities such as when we sleep and wake up, when we eat, and changes in hormone levels. These rhythms, which occur in nearly every species, allow an organism to predict environmental changes and optimize activity, sleep, and food intake patterns throughout the course of a day. There are a few temporary exceptions to animals having a strong rhythm. These include egg-laying ant queens and bee queens, as well as some migrating animals and animals, who spend time in complete darkness either underground or at the North and South Pole. Human exceptions though are rarely due to nature, and more often due to society and technology.

How our bodies respond to food intake is highly dependent on timing, thanks to our internal body clocks. Normally, the human body is prepared for activity and food ingestion during daylight hours[3] and for rest and fasting during darkness. For example, during the day, the liver increases the expression of enzymes involved in storing carbohydrate, while at night the liver[4] favors breaking down carb stores to maintain healthy blood sugar levels during the overnight fast. Although it is also important to efficiently switch[5] from carb breakdown during fasting to carb storage after a meal, from an evolutionary and energetic perspective, it would not be advantageous to express the opposite enzymes (glycogen synthase and glycogen phosphorylase) at high levels throughout the day. Daily fluctuations[6] in transporters for glucose, fructose, and amino acids also indicate that the metabolism of carbohydrate and protein is regulated to maximize absorption during normal mealtimes.

A number of animal studies[7] have found significant differences in metabolic responses to eating within an eight to 12 hour eating window, compared with eating throughout 24 hours, even without altering the quality or quantity of the diet. As you may remember from the rodent study in Study Deep Dives #3, time-restricted feeding patterns support an improved circadian rhythm and are associated with improved body composition, increased endurance, and reduced systemic inflammation, as well as improvement in other biomarkers of metabolic disease. Although the animal research on time-restricted feeding windows is very compelling, there is currently very little human research[8] available. The majority of research that has considered the timing of meals has focused on night-shift workers[9], meal frequency, and people with night-eating syndrome[10], but not very much has been done in healthy, free-living adults.

Analyzing the timing of a person’s self-selected meal patterns is complicated by a number of logistical issues. Methods of data collection can include the use of subjective questionnaires (often during larger studies), food diaries (that provide constant and potentially behavior-changing feedback to the subject), and in-lab video recording that would obviously not reflect the typical food choices of a participant when they’re at home. However, the widespread use of smartphones provides a great new opportunity for researchers to monitor human behavior across a diverse population.

With this in mind, researchers at the Salk Institute near San Diego developed a phone app that enabled them to measure the natural daily eating patterns of free-living healthy adults, while providing minimal feedback to the users. After collecting the data, a pilot feasibility study was undertaken to determine whether reducing the daily eating interval to 10–12 hours without any other attempts to change dietary intake could lead to weight loss in overweight but otherwise healthy individuals.

Circadian rhythms influence the body’s response to a meal. Animal studies have shown that restricting food intake to a window of eight to 12 hours can lead to improved health, although few human studies exist. The use of smartphone apps can aid researchers in tracking eating patterns of free-living adults across a variety of demographic populations. Researchers developed a phone app that enabled them to record the self-selected daily eating patterns of free-living healthy adults.

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