Is Mid-morning Breakfast as Healthy as Early-morning Breakfast for Blood Sugar Control in Adolescent Girls?
Condition: Postprandial Hyperglycemia
MeSH terms: Hyperglycemia
Study type: Interventional

Summary: 
      Repeated, elevated levels of glucose (sugar) within the blood after eating can lead to type 2
      diabetes. In adults, eating breakfast lowers blood glucose responses to subsequent meals when
      compared with skipping breakfast. Yet, adolescent girls may respond differently due to
      differences in how their bodies use energy. This is important because around 80% of the
      United Kingdom (UK) adolescent girls skip breakfast. As common reasons for skipping breakfast
      in adolescent girls are 'lack of time' and 'not hungry' in the morning, eating breakfast
      during the mid-morning may be an attractive option for them. This project will be the first
      to compare the impact of eating breakfast in the early morning and mid-morning with skipping
      breakfast on subsequent blood glucose levels in adolescent girls who usually skip breakfast.
      The findings will inform recommendations tailored to an 'at risk' and under-researched
      population for type 2 diabetes prevention, which is more effective than a cure.
    

Detailed description: 
      Dietary manipulations that can moderate postprandial glycaemia and insulinaemia are at the
      cornerstone of type 2 diabetes (T2D) prevention. Indeed, repeated glycaemic excursions cause
      oxidative stress, inflammation, and atherosclerosis, increasing T2D risk. Adolescence is a
      critical time to promote dietary behaviours that can be sustained across the lifespan. Among
      the dietary factors influencing postprandial glycaemia, the decline in breakfast consumption
      during adolescence in girls is of concern, with only ~20% of UK adolescent girls consuming
      breakfast daily. Cross-sectional and prospective observational studies show that infrequent
      breakfast consumption is associated with T2D risk markers (e.g., glucose, insulin) in
      adolescents and T2D manifestation in adults. Randomised controlled trials in adults suggest
      that improvements in glycaemic control and insulin sensitivity may be key to explaining the
      reduced T2D risk when contrasting breakfast consumption with breakfast omission. Acutely,
      breakfast omission exaggerates glycaemic and insulinaemic responses to subsequent meals when
      compared to breakfast consumption, which has been termed the 'second-meal effect'. Thus, two
      moderate glycaemic responses (with breakfast and lunch) would be potentially better for
      reducing T2D risk than one very large glycaemic excursion (after lunch). Yet, findings based
      on adults may not apply to the distinct hormonal and metabolic profiles of adolescent girls.
      Specifically, it is proposed that the 'second-meal effect' occurs due to increased glucose
      conversion into muscle glycogen in adults. Such responses may differ in adolescents due to
      their higher reliance on exogenous glucose and fat as fuels with a lower reliance on
      endogenous glucose and reduced capacity for muscle glycogen storage, in addition to the 32%
      reduction in insulin sensitivity occurring from pre- to mid-puberty. Unfortunately, current
      knowledge on breakfast and glycaemia in adolescents relies entirely on a few novel studies
      that have pooled data from 13 to 20 year olds with little consideration of pubertal status
      and sex. Hence, the glycaemic responses to breakfast manipulation in adolescent girls are not
      still well understood. Common barriers to consuming breakfast among adolescent girls include
      not being hungry and a lack of time in the morning. As such, the option to consume breakfast
      later in the morning may be an attractive alternative for this population. In terms of
      timing, definitions have proposed that breakfast is consumed within 2-3 hours of waking,
      typically no later than 10:00. Yet, inconsistent definitions have been employed across the
      literature, mainly because evidence to inform a health-based (e.g., focused on glycaemic
      improvements) breakfast timing 'cut-off' is lacking. Thus, the unique contribution of this
      proposal is the use of an experimental cross-over design to directly contrast the effects of
      consuming an early-morning versus mid-morning standardised breakfast with breakfast omission
      on postprandial glycaemia and insulinaemia in adolescent girls classified as habitual
      breakfast skippers. By focusing on adolescent girls, breakfast timing and postprandial
      glycaemia, this proposal is unique, topical and has potential impact for T2D prevention.

      Recruitment:

      Girls will be recruited from local schools after gaining parental informed consent and child
      assent. These schools have expressed an interest in facilitating recruitment for the proposed
      research by providing a platform to invite girls to participate and permission for time off
      school to complete the measures. The participants will be invited to attend an assembly at
      their school and those that wish to discuss their participation with a parent/primary
      caregiver will take an information pack home that includes written details of the study. On
      return of a contact form, students and their primary caregiver will be asked to complete the
      consent, assent and pre-participation health screen questionnaire, before registration on the
      study.

      Experimental design:

      This study will employ a cross-over design. Participants will complete three conditions
      assigned according to the Latin square method: breakfast omission (BO), early-morning
      breakfast consumption (EM-BC) and mid-morning breakfast consumption (MM-BC). The conditions
      will be conducted ~7 days apart in girls who have not started their menses or in the
      early-follicular phase (~28 days apart) in girls with regular menses to minimise the
      potential confounding influence of menstrual cycle phase. In the 48 hours before the
      conditions, dietary intakes, bed time and wake/out of bed times will be replicated, and
      vigorous physical activity will be minimised (as confirmed via accelerometry).

      After an overnight fast, resting metabolic rate (RMR) and substrate oxidation will be
      estimated via expired air analysis, and a capillary blood sample for the measurement of
      plasma glucose and insulin will be taken (~08:15 to 08:30). These measures will be collected
      at regular intervals, with a standardised lunch consumed at 4 h (~12:30) and followed by a
      2-h lunch postprandial period. The standardised breakfast will be provided immediately after
      fasting measures at ~08:30 for EM-BC and 2 hours later at ~10:30 for MM-BC. Participants will
      remain sedentary throughout. Water intake will be replicated between the conditions.

      Test meals:

      A carbohydrate-rich, low glycaemic index (GI) breakfast providing ~70% carbohydrate, ~17% fat
      and ~13% protein will be used. The breakfast will be provided in quantities containing 0.04 g
      carbohydrate per kcal of individualised daily RMR. The standardised lunch providing 0.05 g of
      carbohydrate per kcal of daily RMR will be based on high GI carbohydrate. Meal consumption
      time will be limited to 15 minutes and replicated between the conditions.

      Data and statistical analyses:

      Pre-lunch (4 hours) and post-lunch (2 hours) incremental (iAUC) and total (tAUC) area under
      the curve will be calculated using the trapezium rule for the primary outcomes, plasma
      glucose and insulin. and the secondary outcomes, resting energy expenditure and substrate
      oxidation rates. In addition, peak plasma glucose concentration after lunch will be
      determined.

      Linear mixed models will be used to compare all outcome variables between the conditions.
      Models will include fixed effects for condition (and time for the condition by time analyses)
      and a random intercept for participants, and will be adjusted for the order effect. The
      Holm-Bonferroni correction for multiple comparisons will be applied. Normality will be
      checked using Shapiro Wilk tests. Statistical significance will be accepted at p≤0.05.
      Cohen's effect sizes will be used to gauge the magnitude of differences.

      Sample size estimation:

      Based on 80% power at an alpha level of p=0.05, it is estimated that 21 breakfast skipping
      adolescent girls are required to detect a meaningful between-condition difference (Cohen's
      f=0.36) in post-lunch plasma glucose area under the curve. Recruitment will target 27
      participants across the two study sites to account for an expected 20% attrition rate.
    

Intervention name(s): breakfast omission (BO); early-morning breakfast consumption (EM-BC); mid-morning breakfast consumption (MM-BC)
Intervention type(s): Other; Other; Other
Intervention description(s): this group will not be provided with a breakfast until lunch time (at 12:30).; this group will be provided with an early morning breakfast (at 08:30).; this group will be provided with a mid (late) morning breakfast (at 10:30).
Other intervention name(s): skipping breakfast; early breakfast; late breakfast
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: same participants will complete three breakfast conditions
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: Breakfast; Meal Time; Blood Glucose; Blood Insulin; Adolescents