University of Bath

Calories, clocks and causality

In this inaugural lecture, Professor James Betts presents insights from recent research into human nutrition and how this affects metabolism and physiology.

22 May 20196.05pm
22 May 20197.05pm
Man eating a salad
Too often dietary guidelines simply recommend emulating the eating habits of people who tend to be healthier, yet diet is just one of many reasons why some people may be in better health than others

The simple calorie is a unit of energy (equivalent to 4.2 joules) and is relevant to the fine balance that exists between our diet and our metabolic requirements (i.e. energy intake versus energy expenditure). A caloric deficit can deplete the body’s energy reserves and may impair physiological function (e.g. fatigue), whereas a caloric surplus can expand the body’s energy reserves and may impair long-term health (resulting in obesity for example).

Humans have therefore evolved highly sophisticated feedback mechanisms to regulate the availability of metabolic fuels and maintain energy balance. This is a remarkable feat given that over one billion calories typically enter and exit our bodily system each year. So there are understandably instances when energy imbalances can occur and modern science may present opportunities to help either replenish energy stores following acute depletion (such as post-exercise recovery) or to reduce energy stores following chronic accumulation (weight loss). Unfortunately, nutrition research in general suffers from two key limitations that often render current dietary guidelines incomplete and inaccurate.

Regarding completeness, almost everything we know about nutrition is based on how much we eat and what we eat (quantity and type), yet we are only recently realising the importance of when we eat (time or chrononutrition). Regarding accuracy, too often dietary guidelines simply recommend emulating the eating habits of people who tend to be more healthy, yet diet is just one of many reasons why some people may be more healthy than others (meaning that correlation does not infer causality).

To provide reliable evidence-based recommendations we need to determine whether specific lifestyle changes actually cause any meaningful effects on health, which can be achieved using randomised controlled trials. Such experimental designs have recently been applied to advance our understanding of time in relation to nutrition, from a molecular level through to whole-body physiology.

This inaugural professorial lecture will summarise this new evidence by drawing from a wide range of human research trials that have tested common but often extreme experimental models, including: intermittent fasting (extended morning/evening or alternate-day), time-restricted feeding, continuous feeding, nocturnal feeding, maximal eating occasions and the general scheduling of daily nutrient ingestion relative to time-of-day, usual meal times, sleep and physical exercise. Overall conclusions will reflect the state of current understanding regarding meal timing and circadian rhythms in relation to bodily energy stores, metabolic health and physiological function.