Exercise is recognized as a part of the management of obesity and diabetes. Various protocols of exercise are proposed for the management of obesity, diabetes, and other metabolic diseases. One of the strategies proposed by several authors is low intensity endurance training targeted at the level of maximal oxidation. Large series using this technique are lacking. Addressing this issue, we performed a meta-analysis of the studies on anthropometric measurements. From a database of 433 articles, 15 were selected, including 279 subjects with 6 different populations. Studies duration ranged from 2 months to 12 months. Concerning weight loss, in the intervention versus control analysis, five studies with 185 participants were included with a significant effect size favors exercise (
Exercise training is now widely recognized as a key component of the management of obesity [
Despite the fact that most of these studies involve a little number of subjects and are performed over a short duration of time, it was interesting to review them in a meta-analysis. The aim of this meta-analysis was to give an overall picture of the effects of exercise training targeted on maximal lipid oxidation.
We conducted a research on (1) Pubmed (2) ISI Web of Science from 1994 to 2012, and (3) we also manually searched articles on sciences direct database published from 1994 to 2012 in English or French languages. The year 1994 was chosen being the date of the publication on the crossover concept [
Articles were selected by three different investigators. Differences of opinion for inclusion were resolved by discussion.
Studies were included in the meta-analysis if they met the following criteria: (1) designed as randomized controlled trial or clinical trial, (2) maximal fat-oxidation point was the training method according to the described protocol, (3) participants were males or females affected by chronic diseases without age restriction, and (4) anthropometric measurements and cholesterol were defined as outcomes. If data were duplicated in more than one publication, only the most recent publication was included in the analysis.
Studies were excluded if (1) it was on animal models, (2) the study design was cross-sectional, (3) there was no intervention, and (4) the intervention was on healthy participants.
Descriptive data regarding author, year of publication, pathology, study sample characteristics, type of design, and duration of training protocol were extracted from all selected articles. Weight, waist measurement, fat mass, and serum cholesterol were the selected outcomes.
Because of heterogeneity among included studies, the effect estimates were pooled using a random effects model with the method of DerSimonian and Laird. Firstly, pre- and postintervention mean differences (and their associated standard errors) were pooled for each outcome. Secondly, another analysis consisted of results extracted from randomized controlled trials only to obtain a pooled standardized mean difference of intervention group versus control group. The second analysis was only achieved for the weight outcome as there were less than three included studies that reported mean differences for the other outcomes.
Statistical analyses were performed by using Stata software version 10 (StataCorp. 2007.
Heterogeneity was tested by using Cochran’s chi-square test (Q) to assess the consistency of associations as usual in meta-analysis [
When there were sources of heterogeneity, meta regression was computed to test whether such factors as population, intervention duration, and training type (diet and exercise + diet) had an impact on the final pooled estimates and on the heterogeneity. When moderators were significant, we split the analyses according to this moderator.
Publication bias was examined with the use of funnel plot which is a scatter plot of treatment effect against a measure of study size. The presented funnel plot includes pre- and postintervention mean differences of weight as it is the outcome for which we found the highest number of included studies.
Researches using our different strategies within the different databases retrieved 433 articles. A sum of 60 articles were selected on the basis of their title and abstract, then a total of 15 articles [
Descriptive characteristics of the included studies.
First author | Year | Sample size | Population | Protocol | Number of sessions/week | Duration (months) | Weight |
Waist circumference (cm) | Fat mass |
Cholesterol (mmol/L) |
---|---|---|---|---|---|---|---|---|---|---|
Ben Ounis [ |
2008 | 8 | ObeAdo | REE | 4 sessions of 90 min/week | 2 | −1.9 | −1.8 | −1.7 | −0.21 |
8 | ObeAdo | REE + diet | 4 sessions of 90 min/week | 2 | −11.5 | −12.3 | −1.2 | −0.51 | ||
Brandou [ |
2003 | 14 | ObeAdo | REE | 7 sessions/week during 2 weeks. Then 1/week during 6 weeks | 2 | −3.72 | −3.73 | 0.04 | |
Brandou [ |
2005 | 7 | ObeAdo | REE + diet | 2 sessions of 35 min/week | 2 | −5.2 | −5.07 | ||
Dumortier [ |
2003 | 28 | MetSyn | REE | 3 sessions of 40 min/week | 2 | −2.6 | −3.53 | −1.4 | |
Fédou [ |
2008 | 10 | HIV | REE | Not precised | 12 | −0.92 | −0.01 | −0.28 | |
Ben Ounis [ |
2009 | 18 | ObeAdo | REE | 4 sessions of 90 min/week | 2 | −2 | −2.9 | −2 | |
18 | ObeAdo | REE + diet | 4 sessions of 90 min/week | 2 | −6 | −6.9 | −7 | |||
Dumortier [ |
2002 | 21 | Obese | REE | 3 sessions of 45 min/week | 2 | 0 | |||
Bordenave[ |
2008 | 11 | T2D | REE | 2 sessions of 45 min per week | 2.5 | −3.13 | |||
Ben Ounis [ |
2009 | 9 | ObeAdo | REE | 4 sessions of 90 min/week | 2 | −1.2 | −1.4 | ||
9 | ObeAdo | REE + diet | 4 sessions of 90 min/week | 2 | −9.5 | −5.9 | ||||
Jean [ |
2006 | 28 | T2D | REE | 3 sessions of 45 min/week | 3 | −1.3 | −3.94 | −0.66 | −0.01 |
Romain [ |
2009 | 17 | Psychiatry | REE | not precised | 3 | −2.9 | |||
Venables [ |
2008 | 8 | Obese | REE | 5 sessions of 30 min/week with an incrementation up to 60 min/week | 2 × 4 weeks | −0.2 | −0.1 | ||
Mogensen [ |
2009 | 12 | T2D | REE | 5 sessions of 30 min/week | 2.5 | 0.2 | −2.8 | ||
Elloumi [ |
2009 | 7 | ObeAdo | REE | 4 sessions of 90 min/week | 2 | −1.7 | −10.5 | −1.5 | |
7 | ObeAdo | REE + diet | 4 sessions of 90 min/week | 2 | −12.3 | −12.1 | ||||
Ben Ounis [ |
2010 | 32 | ObeAdo | REE | 4 sessions of 90 min per week | 2 | −4.7 | −8 | −2.8 | |
Maurie [ |
2011 | 39 | T2D | REE | 3 sessions of 45 min/week | 3 | −2.23 |
ObeAdo: obese adolescent, MetSyn: metabolic syndrome, T2D: type 2 diabetes, HIV: human immunodeficiency virus, and REE: training.
Weight, waist circumference, fat mass, and cholesterol are delta values between the beginning and the end-point of the studies.
Flow chart of the study selection.
Several types of protocols were identified. There were studies with only training [
Duration of studies varied from 2 months to 12 months. The study that included people affected by HIV presented the longest followup [
Number of training sessions per week ranged from 2 sessions of 45 minutes to 4 sessions of 90 minutes per week. Two studies [
Concerning the nutritional intervention, the whole studies used hypocaloric diet. One studies set −500 kilocalories (Kcal) per day below the energy requirements at time of the study without precision about the repartition of nutriments [
In included studies, loss of weight varied from 0 Kg to 11.5 Kg and 11 studies reported a significant loss between before and after intervention.
The pooled effect estimate and its associated 95% confidence interval (CI) of weight loss of after versus before intervention was −2.86 Kg (95% CI: −4.07; −1.64) (see Figure
Pooled standard errors and confidence intervals of weight loss in before to after design.
In included studies, loss of fat mass varied from −0.01 Kg to −12.1 Kg and 10 studies reported a significant loss between before and after intervention.
The pooled effect estimate of fat mass loss of after versus before intervention was −4.1 Kg (95% CI: −5.8; −2.3) (
Pooled standard errors and confidence intervals of fat mass loss in before to after design.
In included studies, changes in waist circumference varied from −2.9 cm to −12.3 cm and 7 studies reported a significant decrease between before and after intervention.
The pooled effect estimate of waist circumference change of after versus before intervention was −4.9 cm (95% CI: −6.6; −3.2) (
Pooled standard errors and confidence intervals of waist circumference in before to after design.
In included studies, changes in total cholesterol varied from 0 mmol/L to −0.66 mmol/L and 3 studies reported a significant change between after and after intervention. The pooled effect estimate of total cholesterol of after versus after intervention was −0.26 mmol/L (95% CI: −0.35; −0.17) (
Due to lack of data for fat mass, waist circumference and cholesterol, intervention versus control analysis was only computed for weight.
5 studies which involved 185 participants (128 in the intervention group and 57 in the control group) were included in the analysis. All 5 studies reported significant loss of weight in intervention group compared to control group.
The pooled standardized mean difference of intervention versus control was −0.37 (95% CI: −0.69; −0.06) (
Pooled standardized mean difference and confidence intervals of weight comparing intervention versus control.
All results concerning the moderators are in Table
Results from analyses of moderators.
Moderators | Beta | Standard error |
|
95% CI |
---|---|---|---|---|
Weight | ||||
Population | 1.05 | 0.12 | <0.001 | 0.81; 1.29 |
Duration | 0.25 | 0.20 | 0.23 | −0.17; 0.67 |
Nutrition | −5.09 | 1.47 | 0.003 | −8.18; −2.01 |
Fat mass | ||||
Population | 2.19 | 1.57 | 0.19 | −1.32; 5.70 |
Duration | 1.79 | 2.93 | 0.55 | −4.74; 8.34 |
Nutrition | −6.75 | 0.97 | <0.001 | −8.92; −4.58 |
Waist circumference | ||||
Population | 0.95 | 1.38 | 0.51 | −2.80; 4.90 |
Duration | 2.07 | 2.16 | 0.36 | −2.80; 6.96 |
Nutrition | −5.37 | 1.38 | <0.001 | −8.49; −2.25 |
95% CI: 95% confidence intervals.
Concerning weight loss, the metaregression showed that population (
As population was a significant moderator, we thus split the results according to population (see Figure
Splitting the results according to an intervention in nutrition or not, the mean difference remained significant for intervention only with exercise (−1.95 (95% CI: −3.28; −0.62)) and was larger with interventions including diet + exercise (−6.81 (95% CI: −9.15; −4.47)), without overlap between the CI showing a significant difference between the two interventions. The heterogeneity remained present for intervention without nutrition (
Concerning this outcome, the metaregression showed that neither population (
Thus, separating population according to presence or not of nutritional intervention, the mean difference was significant for interventions that only considered exercise (−1.49 (95% CI: −2.04; −0.94)), and was also larger for intervention including diet and exercise (−8.32 (95% CI: −10.89; −5.74)). As for weight, no overlap was founded between the CI signifying a significant difference between the interventions. There was no heterogeneity in exercise interventions (
The metaregression showed that population was not a significant moderator (
Thus, considering the presence of nutrition or not, the effect of exercise was still significant (−3.51 (95% CI: −4.58; −2.43)) as diet + exercise (−8.87 (95% CI: −11.98; −5.75)) without significant difference due to the overlap between the CI. Then, no heterogeneity was noted either for exercise only (
As there was no heterogeneity in the meta-analysis (
We looked for a publication bias for weight loss between before and after intervention using funnel plot representation (Figure
Funnel plot of weight and its 95% confidence interval in before to after design.
This meta-analysis confirms the conclusions of the individual studies, that are very low intensity training targeted at the level of maximal fat oxidation significantly decreases body weight, fat mass, waist circumference and total cholesterol. On the average, the effects of this variety of training are thus well confirmed, and their average magnitude is more precisely described.
Some methodological aspects of our meta-analysis need to be discussed. First, only 5 studies include a control (nonexercising) group. Actually, we found more studies testing the effect of this method versus caloric restriction group than versus a control nonexercising group. Although all the 5 studies including a control group evidenced a superiority of intervention versus control, the pooled estimate shows a medium size effect on weight loss (−0.37) for the intervention group compared to the control group. This effect size could arise from a lack of power due to the low sample size: 128 intervention subjects versus 57 control subjects. However, if these results may seem low, they can be compared with the meta-analysis from Wu et al. [
The number of studies and especially of randomized controlled trials also requires comments. This number is quite small. Moreover, sample sizes in each study are relatively reduced, as they varied from 6 to 39 subjects. Therefore, there is a lack of large studies and especially of large randomized controlled trials for this variety of training. Another issue we have to discuss is the heterogeneity found in several analyses. Significant heterogeneity was detected for weight, fat mass and waist circumference comparing pre- and postintervention results. This heterogeneity could arise from the heterogeneity of included populations; indeed, participants suffer from various diseases: obesity [
Concerning the duration of interventions, it was not (as it could have been expected) a significant moderator. This could be explained by the fact that only the study from Fédou et al. [
Interestingly, some studies [
Actually, most of these studies used a moderate weekly amount of exercise (in most papers 135 min per week) according to the guidelines available in the early 2000s. It is interesting to point out that such a moderate training protocol has demonstrable metabolic effects, as evidenced by two biopsy studies [
Whether it also modifies resting energy expenditure and resting lipid oxidation and make training more effective over 24 h remains to be studied.
The central questions about such protocols targeted at lipid oxidation levels are as the following: (1) does targeting training at this level of lipid oxidation improve results compared to more standard procedures or not; (2) is the energy deficit the only factor of the therapeutic effect of exercise or does targeting it on lipids make it more efficient? The debate is sometimes passionate but we think that both questions are not yet resolved and deserve careful consideration.
Personal targeting of exercise training is a classic issue in respiratory diseases so that some guidelines recommend it [
Concerning obesity and exercise, there is literature saying that “fat loss depends on energy deficit only, independently of the method for weight loss” [
Studies comparing training targeted on lipid oxidation with other training procedures are scarce. Comparison with aerobic interval training [
If an interesting efficiency of exercise training targeted on lipid oxidation, as suggested by this meta-analysis, were further demonstrated, this method would appear rather attractive because the exercise test used for the targeting is easy to perform and does not require a maximal stress which is not always safe in obese or diabetic patients. In most countries a test before exercise training is required to ensure the safety of the procedure and is most of the time also used for targeting. In obese and/or diabetic subjects exercise calorimetry during a submaximal-graded exercise test could be one of the procedures employed for this purpose.
In conclusion, this meta-analysis shows that training targeted at maximal fat oxidation (mostly used 3 times a week) decreases fat mass and body weight and improves blood cholesterol. This method seems thus to be interesting in chronic diseases such as obesity and diabetes, but this evidence is based on small size studies and a host of issues remain to be clarified. Mostly, large-scale randomized controlled trials are needed to confirm these findings.
There is no conflict of interests.
The authors wish to thank the University Hospital of Montpellier and the National Association of Research and Technology.