Restricting Sugar or Carbohydrate Intake Does Not Impact Physical Activity Level or Energy Intake Over 24 Hours Despite Changes in Substrate Use: A Randomised Crossover

OBJECTIVES: To determine the effects of dietary sugar or carbohydrate restriction on physical activity energy expenditure, energy intake, and physiological outcomes across 24 hours. METHODS: In a randomised, open-label crossover design, twenty-five healthy men (n = 10) and women (n = 15) consumed three diets over a 24-hour period: moderate carbohydrate and sugar content (MODSUG = 50% carbohydrate [20% sugars], 15% protein, 35% fat); low sugar content (LOWSUG = 50% carbohydrate [<5% sugars], 15% protein, 35% fat); and low carbohydrate content (LOWCHO = 8% carbohydrate [<5% sugars], 15% protein, 77% fat). Postprandial metabolic responses to a prescribed breakfast (20% EI) were monitored under laboratory conditions before an ad libitum test lunch, with subsequent diet and physical activity monitoring under free-living conditions until blood sample collection the following morning. RESULTS: The MODSUG, LOWSUG and LOWCHO diets resulted in similar mean [95%CI] rates of both physical activity energy expenditure (771 [624,919] vs 677 [565,789] vs 802 [614,991] kcal·d(−1); p = 0.29] and energy intake (2071 [1794,2347] vs 2195 [1918,2473] vs 2194 [1890,2498] kcal·d(−1); p = 0.34), respectively. The LOWCHO condition elicited the lowest glycaemic and insulinemic responses to breakfast (p < 0.01) but the highest 24-h increase in LDL-cholesterol (p < 0.001), with no differences between the MODSUG and LOWSUG treatments. Leptin concentrations were decreased over 24-h of consuming LOWCHO relative to LOWSUG (p < 0.01). CONCLUSIONS: When energy density is controlled for, restricting either sugar or total dietary carbohydrate does not modulate physical activity level and energy intake over a 24-hour period despite large changes in metabolism. FUNDING SOURCES: This study was supported by The Rank Prize Funds and Kenniscentrum Suiker and Voeding.