Long-term effects of a high-carbohydrate diet and exercise on insulin action in older subjects with impaired glucose tolerance.
Study Goal
The researchers aimed to determine whether a high-carbohydrate diet (HC) alone or combined with exercise (HC-EX) improves glucose metabolism and insulin action in glucose-intolerant adults.
Results Summary
The study found that neither the HC diet nor HC-EX altered fasting glucose or insulin levels or their post-meal response. However, glucose disposal improved slightly under moderate hyperinsulinemia, and muscle glycogen increased significantly only in the HC-EX group.
Population
20 glucose-intolerant adults
Effective Dosage
60% of energy as carbohydrate, 20% as fat
Duration
12 weeks
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
high-carbohydrate diet (HC) | no change | fasting glucose concentrations | 20 glucose-intolerant subjects | - | Neither treatment altered | #1 |
high-carbohydrate diet (HC) | no change | fasting insulin concentrations | 20 glucose-intolerant subjects | - | Neither treatment altered | #2 |
high-carbohydrate diet (HC) | no change | response to a meal | 20 glucose-intolerant subjects | - | Neither treatment altered | #3 |
diet combined with exercise training (HC-EX) | no change | fasting glucose concentrations | 20 glucose-intolerant subjects | - | Neither treatment altered | #4 |
diet combined with exercise training (HC-EX) | no change | fasting insulin concentrations | 20 glucose-intolerant subjects | - | Neither treatment altered | #5 |
diet combined with exercise training (HC-EX) | no change | response to a meal | 20 glucose-intolerant subjects | - | Neither treatment altered | #6 |
high-carbohydrate diet (HC) | increase | glucose disposal | 20 glucose-intolerant subjects | from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 | increased | #7 |
diet combined with exercise training (HC-EX) | increase | glucose disposal | 20 glucose-intolerant subjects | from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 | increased | #8 |
high-carbohydrate diet (HC) | no change | glucose disposal | 20 glucose-intolerant subjects | 49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1 | did not change significantly | #9 |
diet combined with exercise training (HC-EX) | no change | glucose disposal | 20 glucose-intolerant subjects | 49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1 | did not change significantly | #10 |
diet combined with exercise training (HC-EX) | increase | muscle glycogen | 20 glucose-intolerant subjects | 78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glucose/kg muscle | increased | #11 |
high-carbohydrate diet (HC) | no change | muscle glycogen | 20 glucose-intolerant subjects | - | with no changes | #12 |
Carbohydrate metabolism was assessed in 20 glucose-intolerant subjects before and after 12 wk on a high-carbohydrate diet (HC) or the diet combined with exercise training (HC-EX). The diet provided 60% of energy as carbohydrate and 20% as fat. Neither treatment altered fasting glucose or insulin concentrations or their response to a meal. During a glucose clamp (216 pmol insulin/L) glucose disposal increased from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 (P < 0.05) in both groups. During more pronounced hyperinsulinemia (654 pmol/L) glucose disposal did not change significantly (49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1). Muscle glycogen increased in the HC-EX group (78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glucose/kg muscle), with no changes in the HC group. These results do not support the recommendation to increase the dietary carbohydrate content for improving postprandial glucose metabolism or insulin action in glucose-intolerant adults unless combined with exercise training, which promotes muscle glycogen storage.