The big breakfast study: chrono-nutrition influence on energy expenditure and body weight

During the past three decades, the prevalence of obesity has increased worldwide to epidemic proportions and is considered to be a major health problem because of its association with non-communicable diseases, such as cardiovascular disease, stroke and some cancers. Approaches to manage overweight and obesity are likely to be focused around diet and lifestyle solutions to achieve negative energy balance for weight loss, as clinical pharmaceutical and surgical approaches are targeted for morbid obesity. Current dietary advice for weight management is broadly based on the assumption that a 'calorie is a calorie' and it does not matter when these calories are consumed throughout the day. Recent evidence has challenged this assumption, suggesting that we may utilize or expend calories consumed in the morning more efficiently than in the evening, which is a beneficial strategy for weight control. This would mean in practical terms that you would consume more calories at breakfast time as the main meal of the day, and less during the evening meal. In the UK, the main meal of the day is most often in the evening, which pre-disposes to weight gain. These studies suggest that calories are not metabolized equally at all times during the day, and that the process of digestion, absorption and utilization are influenced by the time of day. Studies have not rigorously investigated how time of eating of the main meal of the day influences energy balance. It may be that eating a larger meal at breakfast time leads to being more physically active, or indeed, a larger meal at the evening leads to inactivity. Or, that the natural biological rhythms in the human body are more responsive to calorie ingestion in the morning. After eating, there is an increase in energy expenditure, this is termed, 'thermic effect of food' (TEF). We will explore the mechanisms and time-course of adaption for enhanced morning (breakfast) TEF response as a means to dissipate extra calories, driven by the natural circadian variation in the human (related to light-dark cycle), which can be maximized in the morning for increased energy utilization. An enhanced morning TEF after breakfast could contribute to increased 24-h energy expenditure and, if food intake remained stable, weight loss would thus ensue over time. Numerous authors have studied 24hr energy expenditure particularly in the context of lean-obese differences, but few have considered circadian rhythms and none have studied the interaction with gastric emptying in overweight/obese subjects.

Our hypothesis is that timing of eating influences energy balance and body weight, because morning energy expenditure is amplified in comparison to evening. The cause of the increased energy expenditure in the morning is unclear, whether this is linked to natural biological circadian rhythm or behavioral adaption. This hypothesis will be addressed through conduct of two controlled dietary intervention studies that will examine,

(i) the impact of the time of the main meal of the day (breakfast Vs evening) on metabolic and behavioral regulation during weight loss to establish the biological mechanisms that drive elevated energy expenditure when eating in the morning, in overweight men and women

(ii) whether time of meal consumption effects on energy balance are modulated though the normal biological circadian rhythm

The proposed work aims to show that our current meal consumption pattern in the UK, of having a small breakfast and large evening meal is working against our internal biological clock and this exacerbates the difficulties in successful weight management. From a public health perspective, this chrono-nutrition study offers an opportunity to provide evidence-based data for translational studies on when to eat to promote weight loss. These studies can potentially support the public health message of the importance of a breakfast meal and offers an alternative strategy to promote body weight control.