Introduction 1 2 3 4 6 7 9 10 14 Materials and methods Search strategy Subjects 15 16 17 18 Interventions Outcome measures Type of study Analysis \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{SEM}} = {{\text{SD}}} \mathord{\left/  {\vphantom {{{\text{SD}}} {\surd {\text{n}}\,{\text{and}}\,{\text{SEM}} = {{\left( {{\text{CI}}_{{{\text{upper}}}}  - {\text{CI}}_{{{\text{lower}}}} } \right)}} \mathord{\left/  {\vphantom {{{\left( {{\text{CI}}_{{{\text{upper}}}}  - {\text{CI}}_{{{\text{lower}}}} } \right)}} {2t}}} \right.  \kern-\nulldelimiterspace} {2t}}}} \right.  \kern-\nulldelimiterspace} {\surd {\text{n}}\,{\text{and}}\,{\text{SEM}} = {{\left( {{\text{CI}}_{{{\text{upper}}}}  - {\text{CI}}_{{{\text{lower}}}} } \right)}} \mathord{\left/  {\vphantom {{{\left( {{\text{CI}}_{{{\text{upper}}}}  - {\text{CI}}_{{{\text{lower}}}} } \right)}} {2t}}} \right.  \kern-\nulldelimiterspace} {2t}} $$\end{document} t t Results 1 1 2 Fig. 1 Flow diagram of the literature search. Duplicates: where several studies reported on the same trial and cohort, only one published study for each trial was included for the purposes of this review; the included studies were those that reported on the cohort as a whole, had relevant follow-up measures and included the most recently published data. Where a relevant study was identified in more than one publication, the study was included only once  Table 1 Characteristics of included studies Authors, year Study location/name Study design Intervention duration Number of subjects (men/women) Inclusion criteria Type of intervention Type of dietary intervention Type of exercise intervention Method of physical activity measurement 21 Finland/Finnish Diabetes Prevention Study RCT 3 years 522 (172/350) 2 Exercise and diet Weight reduction through a healthy diet Participants individually encouraged to increase their overall level of physical activity. Circuit-type exercise sessions were also offered. Self-report—Kuopio 12 month leisure time physical activity questionnaire 12 USA/Diabetes Prevention Research Group RCT Average follow-up 2.8 (range 1.8–4.6) years a 2 2 Exercise and diet Weight reduction through a healthy, low-energy, low-fat diet Participants individually encouraged to accumulate at least 150 min/week of moderate intensity exercise. Self-report—Modified Activity Questionnaire and activity log 10 China/The Da Qing IGT and Diabetes Study  RCT 6 years 530 (283/247) IGT (WHO criteria, 1985), age ≥25 years 1. Exercise 2. Exercise and diet 2 2 b Self-report—type not reported 24 Sweden/The 6-year Malmö feasibility study Non-randomised controlled trial 5 years 260 (260/0) IGT (2-h post-challenge glucose values 7–11 mmol/l, and fasting plasma glucose <7.8 mmol/l) Exercise and diet Healthy dietary advice given Participants were encouraged to increase their physical activity levels. Participants given the option of training in organised groups for a 6-month period in the first year. V 2max 19 England RCT 2 years 69 (39/30) IGT (WHO criteria, 1985) Exercise and diet Weight reduction through a healthy, low-energy, low-fat diet Participants were encouraged to undertake 20–30 min of aerobic activity 2–3 days/week. In addition, all participants were given a discount at local gyms. Cardiovascular fitness—shuttle test Self-report—type not reported 22 Netherlands/Study on lifestyle-intervention and impaired glucose tolerance Maastricht RCT 2 years 114 (64/50) 2 Exercise and diet Weight reduction through a healthy, low-energy, low-fat diet Participants were encouraged through goal setting to undertake 30 min of moderate intensity exercise per day and were given use of free exercise classes. V 2max 23 Sweden RCT 1 year 186 (69/117) 2 Exercise and diet Weight reduction through a healthy, low-energy, low-fat diet. Participants were encouraged to increase their physical activity. Supervised exercise sessions were available in the first month V 2max 20 USA RCT 2 years 62 (29/33) IGT (WHO criteria, 1998) Structured exercise and diet Participants were encouraged to follow the energy-balanced American Heart Foundation Step 2 diet Walking/jogging at >70% of heart rate reserve for 1 h on 3 days/week V 2max V 2max a b Table 2 Baseline values and change in main outcomes Authors, year V 2max V 2max a Baseline self-reported physical activity levels a Baseline body mass (kg) a Baseline 2-h plasma glucose (mmol/l) a  Baseline fasting glucose (mmol/l) a Relative risk of diabetes in the intervention group vs the C: group (95% CIs) 21 N/A N/A L: 156 (62 to 288) min/week b` L: 86.7 ± 0.8 Results at 3 years L: 8.9 ± 0.1 Change at 1 year L: 6.1 ± 0.05 Change at 1 year 0.4 (0.3–0.7) C: 169 (65 to 352) min/week C: 6 (−91 to 104) min/week C: 85.5 ± 0.9 b C: 8.9 ± 0.1 b C: 6.2 ± 0.04 L: −0.2 ± 0.04 C: −0.9 ± 0.4 C: −0.3 ± 0.1 C: 0.0 ± 0.04 Change at 3 years Change at 3 years L: −0.5 ± 0.2 L: 0.0 ± 0.05 C: −0.1 ± 0.2 C: 0.1 ± 0.05 12 N/A N/A L: 15.5 ± 0.7 MET-h/week b,c L: 94.1 ± 0.6 b L: 9.1 ± 0.03 NR L: 5.9 ± 0.01 NR 0.4 (0.3–0.5) C: 17.0 ± 0.9 MET-h/week c C: 94.3 ± 0.6 C: −0.1 C: 9.1 ± 0.03 C: 5.9 ± 0.02 10 N/A N/A d d NR D&E: −2.5 E: 8.8 ± 0.1 E: 1.7 E: 5.6 ± 0.1 E: 1.3 E: 0.5 (0.2–0.9) d d E: −0.4 D&E: 9.1 ± 0.1 D&E 1.7 D&E 5.7 ± 0.1 D&E: 1.5 D&E: 0.6 (0.3–0.9) d d C: −1.0 C: 9.0 ± 0.1 C: 4.0 C: 5.5 ± 0.1 C: 2.1 24 L: 2.46 ± 0.04 b N/A N/A c b L: 8.2 ± 01 b NR NR 0.4 (0.2–0.7) C: 2.29 ± 0.1 C: −0.05 c C: 0.2 C: 8.3 ± 0.1 c 19 N/A N/A NR NR L: 85.3 ± 2.9 b L: 9.2 ± 0.1 Change at 1 year L: 6.1 ± 0.1 Change at 1 year N/A C: 85.5 ± 2.5 C: 1.5 ± 0.5 C: 9.2 ± 0.2 L: −0.6 ± 0.3 C: 6.2 ± 0.2 L: 0.0 ± 0.1 C: 0.2 ± 0.3 C: 0.1 ± 0.2 Change at 2 years Change at 2 years L: 0.2 ± 0.3 L: 0.3 ± 0.1 C: −0.5 ± 0.4 C: 0.1 ± 0.2 22 L: 2.15 ± 0.1 b N/A N/A L: 86 ± 1.9 b L: 8.9 ± 0.3 Change at 1 year  L: 5.9 ± 0.1 Change at 1 year N/A  C: 2.13 ± 0.1 C: −0.03 ± 2.77   C: 83.7 ± 1.5 C: 0.1 ± 0.5 C: 8.6 ± 0.2 b C: 5.8 ± 0.1 L: −0.1 ± 0.1          C: 0.3 ± 0.3  C: 0.1 ± 0.1          Change at 2 years  Change at 2 years          b  L: 0.2 ± 0.1          C: 0.8 ± 0.4  C: 0.5 ± 0.1  23 e b,e N/A N/A L: 86.4 ± 1.1 b L: 7.5 L: −0.7 ± 0.2 L: 5.4 L: −0.5 ± 0.1 N/A e e C: 83.6 ± 1.1 C: −0.5 ± 0.3 C: 8.0 C: −0.3 ± 0.3 C: 6.1 C: −0.3 ± 0.1 20 E: 1.93 ± 0.1 b N/A N/A E: 66.5 ± 2.9 b E: 9.2 ± 0.2 Change at 6 months E: 5.3 ± 0.1 Change at 6 months N/A C: 2.02 ± 0.1 C: −0.04 ± 0.03 C: 69.7 ± 2.6 C: 0.6 ± 0.5 C: 9.1 ± 0.2 E: −0.7 C: 5.4 ± 0.1 E: 0.0 C: −0.1 C: 0.1 Change at 2 years Change at 2 years E: −0.6 E: 0.0 C: 0.0 C: 0.1 Data are presented as means±SD or medians (interquartile range) a b p c d e n C D E L MET-h/week NR N/A Study design 10 12 19 23 24 Sample size 12 21 19 19 20 22 Inclusion criteria 10 12 19 24 Sex n 24 Intervention conditions 10 12 19 21 24 20 10 12 19 21 22 24 21 24 19 10 23 20 20 Outcomes 10 12 21 24 19 20 22 23 Incidence of diabetes and physical activity 2 10 10 12 21 12 21 12 25 21 10 24 2-h post-challenge plasma glucose and physical activity 10 21 24 21 10 24 19 22 23 22 22 23 19 26 22 23 19 20 Fasting glucose 24 Discussion 10 12 21 24 10 27 10 28 29 30 10 12 31 19 20 23 19 23 20 21 32 33 20 34 35 36 35 37 In summary, the majority of studies identified for this review used interventions that encouraged dietary and physical activity to initiate and maintain weight loss in individuals with IGT. Analysis of these studies found that the independent effect of physical activity in reducing the risk of type 2 diabetes in individuals with prediabetes is equivocal. Furthermore, given the limited evidence, no definite conclusion can be drawn either as to the amount of physical activity needed to reduce the risk of diabetes in individuals with prediabetes or the effectiveness of a single-component physical activity intervention compared with more conventional multi-component interventions. Thus, more evidence from rigorously designed randomised controlled trials with objective measures of physical activity is needed. As the majority of studies promoting lifestyle changes included in this review failed to substantially increase physical activity levels, strategies for effecting increased physical activity in this population also need to be researched thoroughly. Further investigation is also needed into whether exercise is equally effective in treating the different phenotypes of IGT and IFG.