As a newly-hatched PhD student, it will be a long time before I can base any blog posts on my own (hopefully exciting) research findings. However, exciting research is being produced every single day, and part of my academic work requires that I keep on top of the scientific literature by following a number of different journals (or magazines). During my scientific press-scroll earlier this morning, I came across an impressive metabolic study published in the prestigious journal Cell Metabolism. Impressive for two reasons: 1) its sci-fi nature; 2) its in-depth description of human dietary habits.
“A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits” – that’s the title. Apart from a bit of scientific jargon that may confuse you, what really catches the attention in the study title is “smartphone app”. At least if your brain is slightly tech-freaky like mine. What may have seem like pure futurism a few years ago has now become a reality – not only are smartphone apps integral to our daily lives; because of that, they are slowly taking centre stage in observational studies of human beings. The two US-based authors of this study, Shubhroz Gill and Satchidananda Panda, developed an app to monitor the natural daily eating pattern of 156 healthy adults (both males and females) without laboratory-based restrictions that could otherwise bias the final results. As opposed to previous studies, Gill and Panda were specifically interested in exploring the temporal nature of food and beverage consumption, rather than assessing the quantity and quality of nutrition. To this aim, participants used the app for 3 weeks and submitted feedback in the form of pictures of every food, beverage or water item they consumed, no matter its energy content, just prior to intake.
The wealth of data presented in this paper is astonishing, and its biological relevance even more so. In stark contrast to the self-reported 3 meals/day pattern of feeding from most participants (and thus, conventional wisdom), such breakfast-lunch-dinner structure was largely non-existent. In the top 10 % of the distribution, the mean number of ingestions per day amounted to a staggering 15.52 +/- 0.34 (standard error of the mean), of which 10.55 +/- 0.24 had a caloric content. Moreover, more than 50 % of all calories were consumed after 6 p.m., and only 25 % of caloric intake occurred before noon, which should provide some food for thought for those of us aware of the recommended healthy eating patterns – large breakfasts, minimal caloric consumption in the evening. Overall, the data suggests that eating was a constituent part of wakeful hours, with the body having a break from caloric intake mostly during sleep (the number of reported food consumptions during 1-6 a.m. accounted for <1 % of the data).
Why is this important? Human metabolism is exquisitely tuned to diurnal rhythms, i.e. day/night and the sleep-wake cycle. However, in times of constitutive food intake with near-absent natural fasting (everyday life in developed nations), the internal metabolic clock is overridden with dire consequences for organismal health – partly highlighted in Gill and Panda’s study. They asked the question whether longer eating duration and erratic eating patterns are contributing factors in subjects with co-occurrence of BMI > 25 (overweight) and >14h eating duration. They recruited 8 participants to a 16-week pilot intervention study, which required the former to reduce their eating duration to a self-selected window of 10-12h and to follow this pattern during both weekdays and weekends to avoid metabolic jetlag (observed among the aforementioned 156 participants and defined as delayed onset of food intake on weekends). Strikingly, this modest time-restricted feeding intervention – with no requirement for caloric reduction – resulted in an average weight loss of 3.27 kg (95 % confidence intervals: 0.9081-5.624 kg). When asked to evaluate their sleep satisfaction, hunger at bedtime and energy levels in the mornings as well as over the past few days, participants reported an overall improvement and further expressed an interest in continuing this 10-12h time-restricted feeding without additional supervision. A year later, participants still maintained their weight loss and sleep improvement and felt more energetic. These findings are consistent with extensive studies of intermittent fasting and/or caloric restriction in animal models.
Acknowledging the limitations of the study in terms of sample size and, thus, universality, it is unprecedented in its ability to collect information on the dynamic aspect of human nutrition outside artificial laboratory conditions. The insight gleaned from this study provides a putative explanation behind the association between reduced sleep duration and increased risk for metabolic diseases: increased daily eating duration with associated changes in caloric intake and nutrition quality. Simply by reducing the time period of feeding might thus be enough to impart measurable benefits of clinical relevance on body weight reduction – a crucial finding given the low adherence rate to harsher lifestyle intervention approaches among at-risk individuals.
And finally, I guess one should practice what one preaches – it is 11:02 pm and I have not touched any food since 7-8 pm (at a birthday party), which frankly speaking is a personal achievement these days… Time to give my body a break, and a healthy one indeed.