Following the establishment of causal links between breakfast consumption, the individual components of energy balance, and health it is now important to examine and target the underlying biological mechanisms involved to maximise potential health benefits.

To begin investigating the outlined mechanisms healthy, non-obese participants will be recruited to take part in phase I (acute design) of a wider project.

Causal links between breakfast consumption, the individual components of energy balance, and health have recently been established and it is now important to examine and target the underlying biological mechanisms over a longer period of time to maximise potential health benefits.

Specifically, the substitution of a portion of carbohydrate for protein at breakfast may enhance the potential health benefits of breakfast through targeting distinct mechanistic pathways. Broadly, introducing a greater protein load at breakfast increases insulin secretion and delays gastric emptying, thereby eliciting a potentiated insulin response. In turn this may therefore improve glucose tolerance during a subsequent meal. Additionally, maintenance of euglycaemia following breakfast consumption, coupled with the thermic effect of feeding protein may accentuate the elevated energy expenditure following breakfast observed in previous studies. Finally, both the physical and chemical properties of protein exert a marked satiating effect. Collectively, these mechanisms could interact to maximise the net impact of breakfast on energy balance and associated health outcomes. However, whilst the evidence indicates obvious benefits of feeding a higher protein dose at breakfast, relatively little research has focused on the response to protein over multiple meals/days. Furthermore, and importantly, the mechanisms involved in the second-meal phenomenon and the potential for initial meals of varied composition to target these mechanisms have never been systematically investigated.

To begin investigating the outlined mechanisms healthy, non-obese participants will be recruited to undergo a 4 week intervention study in which they will consume one of three breakfasts for 28-days. The breakfast interventions provide will be:

Carbohydrate rich breakfast

Whey protein enriched breakfast

Extended morning fast

Participants will undergo 7 days of habitual physical activity and diet monitoring prior to visiting the laboratory for their preliminary metabolic assessment in which they will consume the carbohydrate rich breakfast followed by an ad libitum meal for lunch. They will then be randomised to one of the 3 breakfast interventions for 28-days. During the 28-days weekly monitoring of physical activity and energy intake will take place in order to assess energy balance.

Upon completion of the intervention phase participants will revisit the laboratory to replicate the initial visit in which postprandial metabolism was assessed.

Inclusion Criteria:

• Body mass index 18.5-29.9 kg∙m-2
• Age 18-65 years
• Able and willing to provide informed consent and safely comply with study procedures
• Females to maintain record of regular menstrual cycle phase or contraceptive use
• No anticipated changes in diet/physical activity during the study (e.g. holidays or diet plans)
• Inclusive to all breakfast habits (e.g. regular skipper / consumer)

Exclusion Criteria:

• Any reported condition or behaviour deemed either to pose undue personal risk to the participant or introduce bias
• Any diagnosed metabolic disease (e.g. type 1 or type 2 diabetes)
• Any reported use of substances which may pose undue personal risk to the participants or introduce bias into the experiment (e.g. smoking/substance abuse)
• Lifestyle not conforming to standard sleep-wake cycle (e.g. shift worker)
• Any reported recent (<6 months) change in body mass (± 3%)

Where applicable (i.e. the two breakfast feeding interventions) participants will be blinded to the breakfast that they receive for 28-days.