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.
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.
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.
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 (P < 0.05).
Postprandial plasma glucose outcomes may be vulnerable to placebo effects.