Effect of glycemic index and fructose content in lunch on substrate utilization during subsequent brisk walking

Fructose replacement of glucose or sucrose in food or beverages lowers postprandial glucose and insulin without raising triglycerides: a systematic review and meta-analysis

Background: Conflicting evidence exists on the effects of fructose consumption in people with type 1 and type 2 diabetes mellitus. No systematic review has addressed the effect of isoenergetic fructose replacement of glucose or sucrose on peak postprandial glucose, insulin, and triglyceride concentrations.Objective: The objective of this study was to review the evidence for postprandial glycemic and insulinemic responses after isoenergetic replacement of either glucose or sucrose in foods or beverages with fructose.Design: We searched the Cochrane Library, MEDLINE, EMBASE, the WHO International Clinical Trials Registry Platform Search Portal, and clinicaltrials.gov The date of the last search was 26 April 2016. We included randomized controlled trials measuring peak postprandial glycemia after isoenergetic replacement of glucose, sucrose, or both with fructose in healthy adults or children with or without diabetes. The main outcomes analyzed were peak postprandial blood glucose, insulin, and triglyceride concentrations.Results: Replacement of either glucose or sucrose by fructose resulted in significantly lowered peak postprandial blood glucose, particularly in people with prediabetes and type 1 and type 2 diabetes. Similar results were obtained for insulin. Peak postprandial blood triglyceride concentrations did not significantly increase.Conclusions: Strong evidence exists that substituting fructose for glucose or sucrose in food or beverages lowers peak postprandial blood glucose and insulin concentrations. Isoenergetic replacement does not result in a substantial increase in blood triglyceride concentrations.

Post-exercise appetite was affected by fructose content but not glycemic index of pre-exercise meals

The purpose of this study was to investigate whether both glycemic index (GI) and breakfast fructose content affect appetite during the postprandial period and recovery period after 1 hr of brisk walking. Ten healthy young men (age: 21.7 ± 1.5 y, body mass index: 20.9 ± 1.1 kg∙m(-2), VO2max: 53.7 ± 3.7 mL∙kg(-1)∙min(-1)) completed 1 hr of brisk walking at 46% VO2max 2 hr after eating one of three isocaloric breakfasts: a low-GI breakfast not including fructose content (LGI), a low-GI breakfast including fructose beverage (LGIF) and a high-GI breakfast (HGI). All breakfasts provided 1.0 g∙kg(-1) body weight carbohydrates, and the calculated GI values for the three breakfasts were 41, 39, and 72, respectively. In the LGIF and HGI trials, approximately 25% of participants' energy was derived from either fructose or glucose beverage. Appetite scores were measured every 30 min during the 2-hr postprandial period and 1-hr recovery period. During the postprandial period, the incremental areas under the blood response curve values of glucose and insulin were higher in the HGI trial, compared with those in the LGI and LGIF trials. At 30 and 60 min during the recovery period, the appetite scores were lower in the LGIF trial than those in the LGI and HGI trials. No differences were observed between the LGI and HGI trials. Breakfast fructose content, rather than GI, seems to affect appetite during the recovery period after 1 hr of brisk walking.

Fructose Alters Intermediary Metabolism of Glucose in Human Adipocytes and Diverts Glucose to Serine Oxidation in the One-Carbon Cycle Energy Producing Pathway

Increased consumption of sugar and fructose as sweeteners has resulted in the utilization of fructose as an alternative metabolic fuel that may compete with glucose and alter its metabolism. To explore this, human Simpson-Golabi-Behmel Syndrome (SGBS) preadipocytes were differentiated to adipocytes in the presence of 0, 1, 2.5, 5 or 10 mM of fructose added to a medium containing 5 mM of glucose representing the normal blood glucose concentration. Targeted tracer [1,2-¹³C₂]-d-glucose fate association approach was employed to examine the influence of fructose on the intermediary metabolism of glucose. Increasing concentrations of fructose robustly increased the oxidation of [1,2-¹³C₂]-d-glucose to ¹³CO₂ (p < 0.000001). However, glucose-derived ¹³CO₂ negatively correlated with ¹³C labeled glutamate, ¹³C palmitate, and M₊₁ labeled lactate. These are strong markers of limited tricarboxylic acid (TCA) cycle, fatty acid synthesis, pentose cycle fluxes, substrate turnover and NAD⁺/NADP⁺ or ATP production from glucose via complete oxidation, indicating diminished mitochondrial energy metabolism. Contrarily, a positive correlation was observed between glucose-derived ¹³CO₂ formed and ¹³C oleate and doses of fructose which indicate the elongation and desaturation of palmitate to oleate for storage. Collectively, these results suggest that fructose preferentially drives glucose through serine oxidation glycine cleavage (SOGC pathway) one-carbon cycle for NAD⁺/NADP⁺ production that is utilized in fructose-induced lipogenesis and storage in adipocytes.

Effect of the glycemic index of pre-exercise snack bars on substrate utilization during subsequent exercise

PURPOSE

To investigate the effect of the glycemic index (GI) of pre-exercise snack bars on substrate utilization during subsequent moderate intensity exercise.

METHODS

Fourteen male participants (Age: 27 ± 5 yr; BMI: 22.5 ± 2.7 kg m(-2); [Formula: see text]: 48.7 ± 6.1 mL kg(-1 )min(-1)) completed two trials in a randomized and counterbalanced crossover design. Two iso-caloric snack bars with different GI values (20, LGI versus 68, HGI) were provided to the participants. Ninety minutes later, all participants completed 45 minutes of ergometer cycling at 65% [Formula: see text]. Substrate utilization was measured using indirect calorimetry.

RESULTS

During exercise, higher fat oxidation and lower carbohydrate (CHO) oxidation were observed in the LGI trial (LGI versus HGI: CHO, 87.3 ± 20.1 versus 99.2 ± 19.0 g, p < 0.05; Fat, 15.0 ± 5.8 versus 9.7 ± 7.0 g, p < 0.05).

CONCLUSION

Compared with an iso-caloric HGI snack bar, pre-exercise LGI snack bar consumption may facilitate a shift of substrate utilization from CHO to fat during subsequent moderate intensity exercise.