When a placebo is not a ‘placebo’: a placebo effect on postprandial glycaemia

Authors

  • John L. Sievenpiper,

    1. Risk Factor Modification Centre, St Michael's Hospital and Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
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  • Adish Ezatagha,

    1. Risk Factor Modification Centre, St Michael's Hospital and Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
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  • Anamaria Dascalu,

    1. Risk Factor Modification Centre, St Michael's Hospital and Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
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  • Vladimir Vuksan

    1. Risk Factor Modification Centre, St Michael's Hospital and Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
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Vladimir Vuksan, PhD, Risk Factor Modification Centre, St Michael's Hospital, #6138–61 Queen Street East, Toronto, ON, M5C 2T2, Canada.
Tel: + 1 416 867 7450
Fax: + 1 416 867 7442
E-mail:v.vuksan@utoronto.ca

Abstract

What is already known about this subject

• Although placebo effects have been shown on subjective continuous variables such as pain, placebo effects on objective continuous variables remain uncertain.

• The present, pilot, follow-up investigation represents the first to assess a placebo effect on the objective continuous measurement of acute postprandial plasma glucose.

What this study adds

• Placebo effects may be operating on postprandial plasma glucose outcomes.

• Cornstarch sources of placebo may decrease the plasma glucose response to a 75-g oral glucose tolerance test, rendering them as positive controls when assessing postprandial outcomes.

• Other carbohydrate sources used as placebos in research may show similar effects.

Aims

Placebo effects in clinical trials remain uncertain. To investigate a placebo effect on acute postprandial plasma glucose, we conducted a follow-up investigation on a previous study.

Methods

The effect of placebo (9 g encapsulated cornstarch +500 ml water, taken at −40 min) on the plasma glucose response to a 75-g oral glucose tolerance test (OGTT) was assessed in a previous study in 12 healthy subjects (gender, five male, seven female; age 27 ± 6 years; body mass index 24 ± 3.4 kg m−2). This was compared with the effect of a water control (500 ml water taken alone at −40 min) on the same outcome in the same subjects in a follow-up study.

Results

Cornstarch placebo decreased plasma glucose area under the curve during the 75-g OGTT by 28% [Δ (95% confidence interval) −63.3 min mmol−1 l−1 (−218.33, 91.66), P < 0.02] compared with the water control (< 0.05).

Conclusions

Postprandial plasma glucose outcomes may be vulnerable to placebo effects.

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