Increased Salivary Cortisol Reliably Induced by a Protein-Rich Midday Meal

Increased Salivary Cortisol Reliably Induced by a Protein-Rich Midday Meal

E. Leigh Gibson, PhD, Stuart Checkley, MB, BCh, FRCP, FRCPsych, Andrew Papadopoulos, MSc, PhD, MRSC, Lucia Poon, RMN, Sarah Daley, BSc and Jane Wardle, PhD

From the Health Behaviour Unit, Department of Epidemiology and Public Health (E.L.G., J.W.), University College, London; Institute of Psychiatry (S.C.), DeCrespigny Park, London; Bethlem and Maudsley NHS Trust (A.P., L.P.), Beckenham, Kent; London Hospital Medical School (S.D.), Whitechapel, London, United Kingdom.

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Fig. 1. Design of Experiment 1 showing sequence of high-protein midday meals versus no meal. Note: Days 2 and 3 did not immediately follow the respective preceding days (1 or 2).

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Fig. 2. Effects of two identical high-protein midday meals on salivary cortisol levels, compared with a day on which no meal was served (Meal A ${blacktriangleup}$ ; Meal B •; No Meal ${square}$ ). Data are expressed as mean ± SE (N = 10). ab, ${Delta}$ -cortisol at this time differed significantly from No Meal for Meal A and for Meal B: Bonferroni t tests, t (9) = 3.44, p < .05; t(9) = 4.78, p < .01, respectively. For unit conversion, µg/dl = nmol/liter x .03625. (Note that time is given in the European or military form.)

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Fig. 3. Changes in salivary cortisol levels in women after eating a high-protein meal (•, 32% energy as protein; 630 kcal) and an equicaloric low-protein meal ( ${circ}$ , 5% energy as protein). Data are expressed as mean ± SE (N = 9). *Significantly greater than cortisol levels after the low-protein meal: at 30 minutes, t(8) = 2.30, at 60 minutes, t(8) = 2.59, p < .025, 1-tail. +Significantly less than baseline (12:30 PM) cortisol levels, t(8) = 3.92, p < .01. #Significantly greater than baseline cortisol levels, t(8) = 2.27, p < .05, 1-tail. (Note that time is give in European or military form.)

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Fig. 4. Scattergram of GHQ-12 scores versus difference between meals in peak ${Delta}$ -cortisol (nmol/L) (Experiment 2). The line is plotted by linear regression (R² = .74).

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Fig. 5. Changes in positive (upper panel) and negative (lower panel) affect (PANAS scores, differences from premeal baseline) in women after eating a high-protein meal (•) and an equicaloric low-protein meal ( ${circ}$ ). Data are expressed as mean ± SE (N = 9). *Significantly greater than mean affect (at that time) after the low-protein meal. +Significantly different from baseline (zero at 1230 h). See text for statistical details.