This study aimed to assess the effect of varying intensity of physical activity on body composition during an intervention period of 6 months. The findings show that, when incorporating an MPA program based on aerobic exercises to a dietary regime, weight loss improves significantly. Also, women’s body composition shows a definite improvement. In this case, MPA raised the BF loss to − 6.21% (± 2.95%) after 3 months, and to − 10.57% (± 3.45%) after 6 months. These losses are significantly higher than those in the control group. However, the most significant fat loss was achieved by the group performing IPA, which showed a decrease of − 16.31% (± 5.91%) after 6 months. It also found that, after a caloric restriction (CON), the loss of MM reached up to − 3.66 ± 2.19 kg after 6 months.
The intervention showed that the best intensity for carrying out PA is the intense one, due to its influence on body composition. After 3 months, the MM loss was significantly less than for the other groups (− 0.10 ± 4.46 Kg). More importantly, after 6 months, the group doing IPA was the only one that gained MM (0.99 ± 4.96 Kg). Therefore, it is of interest to observe how a combination of aerobic and anaerobic training permits, not only to conserve but also to increase MM, which suggests that the weight loss triggered by the IPA is of better quality than that produced by the rest of the interventions studied. In short, the main results obtained demonstrate that weight loss is significant in the short-term (3 months), when consuming a hypocaloric diet (with an energy deficit of 500 kcal/day), with no need of PA. However, weight loss in the mid-term (6 months) will depend on incorporating measured and controlled physical activity, irrespective of its typology or intensity (moderate or intense).
Finally, it manifest that the body composition changes in the short term when a diet and a physical activity plan are followed (independently of the exercise intensity). It is only through intense physical activity that a reduction in the BF can achieve, together with maintenance or increase in FFM. These two parameters are of great importance to evaluate the quality of the weight loss.
Comparison with existing literature
Concerning body weight, it has been shown that a one-off nutritional intervention may trigger a moderate loss of weight (from 5 to 10%) in middle-aged adult women, and in post-menopausal women ≥50 years, in comparison with their initial weight . These data are in agreement with the results presented in this study, in which a weight reduction of 6.32 ± 2.68% found in the control group after 6 months.
Other works focusing their analysis on the effectiveness of PA together with caloric restrictions [38,39,40,41] conclude that the difference in weight loss in the group only following a diet is moderate (from 1 to 2 extra kg). These results are similar to those found after the present intervention, in which there were no significant differences in weight loss in the study groups after 3 months.
Contrary to findings presented by other authors , no sustainable weight loss can ensure in adult women only with negative caloric balances mediated by a caloric restriction after 3 months. Furthermore, after 6 months, the weight loss amongst the women who only followed the nutritional intervention was significantly less, in comparison with the women with a PA and a diet plan. These differences at 6 months, compared with those founds in previous works, could be due to variations in the study design. All groups, regardless of the PA prescribed, were equally submitted to a negative caloric balance induced by a caloric restriction of 500 kcal/day. This enabled evaluation of the total body weight evolution with greater precision, unlike other studies in which the energy balance was not rigorously controlled [43, 44].. Also, there is evidence that women, in contrast to men, show a greater need to compensate their appetite after a caloric restriction, and that this compensation is not closely related to doing acute exercise . Therefore, we consider that monitoring and controlling the dietary intake allows us a better understanding of weight loss evolution in women.
During the intervention, it found that the MPA group achieved the most considerable weight reduction during the first 3 months, a trend that continued in the second term. This finding confirms the conclusions of Mayer in the 1950s, in which the activity intensity described as “range of normal activity,” and which was recently redefined by Blundell et al. as a “regulation area.”  Also, we know that a lower level of energy expenditure (CON) may imply a disconnection between intake and caloric expenditure . PA performs an essential part in regulating satiety. This research has shown that a moderate-intensity exercise program helps patients reach higher levels of satiety than those with a sedentary lifestyle, thus representing the ideal PA threshold for losing weight.
The MM gain has explained the smaller weight loss produced by doing PA. Similar to findings from other research, and this is due to strength exercise being a stimulant of growth and muscular maintenance in adult women, absorbing the weight loss [48,49,50].
Focusing the analysis on body composition, the women submitted to caloric restriction lost their BF for a limited time. After 3 months, BF loss in the control group was a mean of − 3.96% (± 3.48%), corroborating with results from other studies [51, 52]. However, at 6 months, there was a recovery of BF in this group, with an overall reduction at the end of the intervention of − 3.56% (+ 3.13%).
The explanation for this could be found in the aforementioned “regulation area,” that relates adipose tissue accumulation to the small amounts of energy expended. Regular exercise at a tolerable threshold acts as an appetite modulator and, as other investigations have shown, in a reduced PA scenario the patient tends to eat in excess or an opportunistic manner [53, 54].
The loss of muscle mass after caloric restriction (CON) that reached up to − 3.66 ± 2.19 Kg at 6 months was less pronounced amongst women who carried out MPA, mitigating it to − 3.23 ± 1.97 Kg at 6 months, with a slight recovery of the MM lost at 3 months (− 3.66 ± 1.97), similar to that reported by other authors .
These results are reaffirmed in the multivariant study. Following the same caloric restriction dietary pattern, the changes in body composition will depend on the type of physical activity. Here, intense physical activity achieved better results in BF loss (ßstand. = − 0,436) and a gain in, or maintenance of, MM (ßstand. = 0,182) and confirms the findings of other authors (Friedenreich et al., 2011). Provided it is possible, intense physical exercise should be recommended in this group of women.
From this perspective, it is essential to emphasize the importance of losing weight correctly, as defined by a reduction in body fat percentage with no impact on the MM. Meanwhile, a loss of MM causes an increase in the risk of suffering from sarcopenia . That is to say, a quality weight loss would enjoy the benefits of BF loss without the risks of MM loss. Besides, evidence has shown that PA improves behavior patterns that prevent the rebound effect once the controlled intervention has ended .
Previous studies reported that decreases in the MM were restored overtime after weight loss interventions [57, 58]. Although the MM loss was lower than that of total BF, muscle maintenance must be monitored and prescribed even in weight loss programs. The subjects of our study who had a sedentary or moderate exercise prescription, that is, walking, lost muscle mass at the end of the period. The explanation for this is that this kind of PA seems insufficient for mobilizing and stimulating muscle mass . The group in our study that had an intense physical exercise prescription, i.e., incorporating resistance training, was the only one that showed a mass muscle gain at 6 months. These results might evidence that a combined program of aerobic and resistance-type exercise helps to preserve muscle mass during weight loss, results that matched those of a recent review .
Our findings reveal a significant body fat loss in the prescription of PA; the higher the intensity of PA, the greater the loss of fat at 6 months. While sedentary instruction implied a 3% fat loss at 6 months, the IPA subjects reached 16%. Also, when analyzing the results among MPA and IPA subjects, we observed that they lost an additional 6% of fat, while we did not find a significant weight loss. Our results are consistent with the existing literature ; although high-intensity training did not improve the weight loss in an interval of 6 months compared to a lower intensity, the impact on the fat loss was significant .
Strengths and limitations
For this clinical study, the sample size was 60 participants. All of the patients were in a similar baseline in order to undertake a better assessment at the end of the research. To evaluate the changes and the importance of the physical activity on the body composition, the study was based on an exercise plan with two intensities (moderate and intense). The study has limitations because the sample is limited to sedentary, overweight or obese, adult women. Thus, further investigations should be necessary to clarify if these results could extrapolate to men. Although the sample size is similar to that used in previous works [63, 64], we carried out a randomization procedure that led to balanced arms. Also, a 20% attrition rate would expect at 6 months, and the study saw a slightly higher rate of 25%. While attrition was more significant than was intended, it is similar to observed in several other physical activity weight-loss interventions [65, 66]. No differential attrition rates were found between groups in the present study. To avoid the self-report bias, previously documented , the data collection records check out by the research staff in face-to-face consultations weekly. A control without caloric restriction was not added to this study because the effect of the diet was not the primary objective to design this investigation, using as a control group the sedentary one. To further investigate how diet could affect behavior during a weight loss program, a non-restricted group might be interesting.
Although a period of 6 months is considered to be adequate to draw meaningful results and valuable conclusions, future studies with longer monitoring periods will be beneficial to confirm whether the trend regarding the MPA and IPA has been maintained.
Lastly, it will also be beneficial for further research to include a fourth group with no diet assigned. This will help to assess whether body composition can improve in the short, medium and long term with only PA.